freecalypso-docs: FC-handset-spec annotate

annotate FC-handset-spec @ 46:1fec0a3f09cc

FC-handset-spec: audio routing documented

author	Mychaela Falconia <falcon@freecalypso.org>
date	Thu, 10 Jun 2021 21:43:50 +0000
parents	9df8683daec4
children	f0419ac0a815

rev	line source
41 7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	1 FreeCalypso Handset Specification
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	2 =================================
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	3
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	4 The purpose of this document is two-fold:
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	5
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	6 1) This document serves as the principal design specification for the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	7 FreeCalypso Libre Dumbphone handset hardware which I, Mother Mychaela,
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	8 seek to build.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	9
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	10 2) This document also defines the scope of functionality to be supported in
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	11 FreeCalypso handset firmware, including support for additional hardware
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	12 targets beyond the primary FC handset hw target.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	13
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	14 1. FC handset hardware specification
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	15
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	16 1.1. Basic features
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	17
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	18 The Mother's goal is to produce a replacement for the proprietary Pirelli DP-L10
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	19 phone, or more specifically, for the GSM-only subset of this Pirelli phone which
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	20 the Mother actually uses, without Pirelli's key differentiating feature of
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	21 non-GSM WiFi operation, and without Pirelli's camera. The following hardware
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	22 features are to be included:
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	23
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	24 * 176x220 pixel color display (no touch)
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	25 * 21-button main keypad
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	26 * 3 side buttons for volume control and an auxiliary function
42 6b61d77f7700 FC-handset-spec: missed the loudspeaker and vibrator in 1.1 Mychaela Falconia <falcon@freecalypso.org> parents: 41 diff changeset	27 * hands-free loudspeaker
6b61d77f7700 FC-handset-spec: missed the loudspeaker and vibrator in 1.1 Mychaela Falconia <falcon@freecalypso.org> parents: 41 diff changeset	28 * vibrator
41 7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	29 * USB port that combines charging and computer interface
46 1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	30 * wired analog headset jack
41 7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	31 * single SIM slot
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	32
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	33 The following features which are commonly found in mainstream proprietary
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	34 phones, particularly more recent ones, will NOT be included:
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	35
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	36 * camera
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	37 * Bluetooth
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	38 * FM radio
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	39 * TV receiver
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	40 * GPS receiver
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	41 * dual SIM slot
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	42 * torch light beyond LCD and keypad backlights
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	43
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	44 1.2. RF band capability
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	45
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	46 Our FC handset needs to be quadband GSM; this quadband capability will be
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	47 achieved by copying the RF section and the core PCB layout around it from the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	48 reverse-engineered iWOW TR-800 modem module, which is itself a very direct
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	49 (almost verbatim) derivative of TI's Leonardo+ quadband reference design.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	50
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	51 1.3. RAM and flash
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	52
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	53 The Mother's intent is to use Spansion S71PL064JA0 flash+RAM MCP on the final
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	54 handset motherboard, providing 8 MiB of flash and 2 MiB of XRAM in a 7x9 mm
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	55 footprint. This flash and RAM capacity is already known to be fully sufficient
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	56 for our FreeCalypso handset firmware in maximal feature configuration, hence
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	57 any larger capacity would be excessive. However, on our FC Venus development
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	58 board we may use the larger S71PL129NC0 MCP, same as used on FCDEV3B V2.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	59
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	60 1.4. Liquid crystal display
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	61
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	62 1.4.1. Display size
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	63
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	64 The size of the display for our FC Libre Dumbphone handset design is fixed at
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	65 176x220 pixels, 16-bit color, following TI's D-Sample platform and the starting
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	66 point UI code that was developed for it. Thoughts of changing to a different
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	67 display size have been considered and rejected:
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	68
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	69 * If we were to change to a smaller display size, we would have to do extra work
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	70 on the firmware to shrink the UI to the smaller size, and we would reduce the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	71 amount of information that can be displayed at once. We would incur extra
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	72 work and a functional loss, but gain absolutely nothing in return.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	73
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	74 * If we were to change to a larger display size (240x320 pixels seems to be the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	75 largest reasonable size for dumbphones, used in high-end Nokia models), we
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	76 would be venturing into uncertain territory - the greatest uncertainty would
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	77 be the extra CPU load on Calypso to draw the larger UI and to refresh the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	78 larger framebuffer, which is done with PIO on Calypso, without any DMA
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	79 assistance. The D-Sample LCD size of 176x220 pixels already appears to be a
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	80 strain in some drawing code paths, hence the Mother's decision is to play it
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	81 safe and stick with the known working display size. Expanding the UI to make
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	82 sensible use of larger screen real estate would also entail additional work.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	83
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	84 176x220 is the display size in pixels, and this resolution number by itself says
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	85 nothing about the physical display size in inches or mm. However, most readily
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	86 available LCDs that are made for this pixel resolution are made in 2.0" diagonal
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	87 physical size, with 31.68x39.60 mm active area and 0.180 mm dot pitch, hence
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	88 this physical size is the one we are going to use.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	89
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	90 1.4.2. Specific LCD module selection
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	91
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	92 As of this writing, the specific LCD module to be used has not been firmly
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	93 selected yet. We are actively looking for an LCD module that fits all of the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	94 following requirements:
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	95
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	96 * TFT color LCD, 2.0" diagonal, 176x220 pixel resolution;
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	97
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	98 * 16-bit microprocessor bus interface;
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	99
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	100 * 6:00 viewing direction as appropriate for cellular handsets;
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	101
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	102 * backlight consisting of 3 white LEDs in parallel, joined at the anode,
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	103 with separately brought-out cathodes;
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	104
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	105 * mechanical design that supports mounting with the FPC tail folded under the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	106 module, either by way of direct solder termination (no connector) or by way
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	107 of raised sides that create sufficient vertical space to accommodate the FPC
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	108 connector.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	109
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	110 The requirement of 16-bit microprocessor bus interface stems from the desire to
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	111 interface this LCD to the Calypso in exactly the same way how TI did it on the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	112 D-Sample, the 6:00 viewing direction and mechanical mounting requirements stem
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	113 naturally from the target application (cellular phone handset), and the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	114 backlight LED wiring requirement stems from the constraints of our chosen
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	115 MAX1916 backlight LED driver chip - see section 1.4.4.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	116
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	117 1.4.3. Backlight and readability considerations
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	118
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	119 Out of the various pre-existing mobile phones which I (Mychaela) have
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	120 experienced, there have been 3 different kinds of LCDs in terms of how display
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	121 operation and readability interacts with the backlight:
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	122
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	123 1) older phones with black&white LCDs: on all phones of this type which I've
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	124 ever used, the display is perfectly readable without the backlight given
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	125 ordinary ambient lighting, be it natural daylight or room lighting. Such
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	126 LCDs are called reflective. With these B&W displays, you only need to turn
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	127 on the backlight if you need to operate the phone in darkness, such as
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	128 outdoors at night or inside with all lights off. The firmware in such phones
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	129 is typically designed to leave the actual display functional and updated at
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	130 all times, with only the backlight subject to on/off control.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	131
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	132 2) most newer phones with color displays, of which Pirelli DP-L10 is a
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	133 representative case, have transmissive LCDs that are not designed to be
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	134 readable without the backlight at all - backlight required for readability
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	135 (BLRR) is another way to describe such LCDs. Because the display is not
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	136 readable at all without the backlight, phone firmware is typically designed
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	137 to turn off the entire display (not just the backlight) when the screen goes
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	138 dark, and operation visible to the user is display on/off, rather than
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	139 backlight on/off. It is a good firmware design practice to "swallow" the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	140 initial keypress that turns on the display from dark state, i.e., to block
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	141 the regular action of whatever button was pressed to "wake up" the display.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	142
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	143 3) The color display on Motorola C139 phones is an odd intermediate case: this
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	144 display is NOT practically readable with the backlight off, yet the firmware
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	145 is designed as if the display were readable in this condition: the actual
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	146 display (unsure if it is CSTN or TFT) remains on and updated, and when you
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	147 press some button to "wake up" the display, that button still takes its
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	148 regular action, which is really bad for usability. How do we know that the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	149 actual CSTN or TFT display remains on and actively updated when it is not
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	150 readable with the backlight off? Answer: the non-backlit display can be made
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	151 readable by shining a flashlight directly at it - but this trick requires a
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	152 directly pointed flashlight; no amount of ordinary ambient light is enough
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	153 to make the display readable.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	154
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	155 Because our FC Libre Dumbphone handset will have a color display (contemporary
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	156 TFT) and because we are sane, not copying the monumental design mistake of Mot
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	157 C139, our display will fall into class 2 by the above classification: backlight
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	158 required for readability, full display on/off rather than just backlight on/off,
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	159 firmware operating like Pirelli's in terms of wake-up keypress swallowing.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	160
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	161 1.4.3.1. Backlight dimming mode
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	162
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	163 Because our LCD is of BLRR type and because we seek to fully replicate Pirelli's
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	164 logic in terms of when keypresses are swallowed and when they are not, we need
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	165 to implement a dimming mode for our LCD backlight. In Pirelli's design which we
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	166 are copying, when you are playing with phone menus or composing SMS etc, but are
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	167 not in an active call, the display switches between full brightness and totally
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	168 off - it goes fully off on timeout, and when you press a button to wake it up,
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	169 it switches on at full brightness, together with the keypad backlight. But when
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	170 you are in a call, when the timer expires (and it's a shorter timer, 10 s
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	171 instead of 30 s), the display goes dim instead of fully off, and in this dimmed
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	172 (but still readable) state keypresses are NOT swallowed.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	173
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	174 We only need to implement two different intensity levels for the LCD backlight:
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	175 full brightness and in-call dimmed. The backlight intensity level in the dimmed
43 e1b75668a706 FC-handset-spec: grammar fix Mychaela Falconia <falcon@freecalypso.org> parents: 42 diff changeset	176 state will need to be chosen on this principle: use the lowest backlight LED
41 7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	177 current (to conserve battery power and allow longest talk time on one charge) at
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	178 which the display is still readable, similarly to Pirelli's in-call dimmed
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	179 state.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	180
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	181 In the user-actively-poking state, as opposed to the long-call dimmed state,
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	182 there is no need to provide different configurable backlight levels - see
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	183 section 1.4.5.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	184
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	185 1.4.4. Backlight circuit implementation
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	186
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	187 In all candidate TFT LCD modules that are being considered (see section 1.4.2),
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	188 the backlight consists of 3 white LEDs wired in parallel, joined either at the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	189 anode or at the cathode - although as we shall see momentarily, we require an
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	190 LCD module where the 3 LEDs are joined at the anode, with the 3 cathodes brought
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	191 out separately. LCD module datasheets call for 15 mA current through each LED
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	192 at maximum intensity, for 45 mA total, and the LED forward drop voltage (Vf) at
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	193 this rated current seems to range between 2.9 V (what I actually measured on one
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	194 candidate LCD module) to 3.2 V (what the datasheets list as typical) to perhaps
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	195 as high as 3.4 V (what one datasheet lists as the maximum).
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	196
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	197 Given the parallel (as opposed to series) wiring of the 3 LEDs and the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	198 relatively low Vf, there is no need to use any kind of boost converter as part
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	199 of the LED driver circuit for this backlight - any boost converter will only add
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	200 inefficiency (more current will be drawn from the battery for the same LED
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	201 current), hence we need to avoid using such.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	202
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	203 Regardless of whether a given phone design uses a boost converter or not (it
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	204 seems that older designs do use boost converters, either because older white
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	205 LEDs have higher Vf or because 2 or 3 LEDs are wired in series), all traditional
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	206 phone designs seem to share the quality where the display backlight brightness
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	207 remains the same as the battery discharges and as Vbat goes down - this quality
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	208 was directly observed on the Pirelli DP-L10 (unknown circuit design) and
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	209 inferred from the available schematics for Mot C139 and C155, with both of the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	210 latter boost-converting to fixed 5.0 V. In our case, even though we choose to
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	211 not use a boost converter for efficiency reasons, we still need to achieve the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	212 quality of the display brightness remaining the same through the discharge range
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	213 of our Li-ion battery - having the display dim in half as the battery discharges
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	214 from 4.2 V peak to 3.6-3.7 V plateau is simply not acceptable.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	215
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	216 The simplest possible LED driving circuit would be one where a current limiting
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	217 resistor is inserted in series with each LED, and then the 3 parallel
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	218 LED+resistor sets are connected across battery terminals, with a transistor
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	219 inserted somewhere to act as the on/off switch. However, this trivial circuit
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	220 is not suitable in our application because it would produce unacceptably large
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	221 variation in display brightness as the battery discharges - hence we need a more
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	222 intelligent LED driving circuit. Our Luna LCD carrier board from the spring of
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	223 2020 features an LDO bringing Vbat down to fixed 3.5 V, followed by very low-
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	224 value resistors in series with each LED - but this approach is not good for
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	225 production either, as it makes the LED current extremely sensitive to any slight
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	226 variations in Vf.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	227
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	228 Fortunately, I was able to find a specialized white LED driver chip that is just
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	229 perfect for our application, or more precisely, a specialized chip that acts as
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	230 a constant current sink for such LEDs - Maxim MAX1916, design from 2001, just
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	231 the right time frame for the kind of phone we are seeking to build. This
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	232 special chip takes the place of "dumb" ballast resistors: connect Vbat (battery
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	233 positive terminal) directly to the common anode of the 3 LEDs, but instead of
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	234 series resistors, connect each cathode to the corresponding LEDn pin of MAX1916
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	235 - without any resistors or transistors! FETs inside the MAX1916 take the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	236 place of resistors as current-limiting elements, and the chip's global on/off
44 a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	237 control (which will be driven with a Calypso GPIO) takes the place of a separate
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	238 switching transistor.
41 7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	239
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	240 The special quality of MAX1916 is that it produces constant current through each
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	241 LED (based on a set reference current and 230x current multiplication circuit
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	242 inside the chip) regardless of variations in both Vbat and Vf! Of course the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	243 requested current can only be sustained as long as Vbat >= Vf + Vds, where Vds
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	244 is the lowest drop voltage of the FETs inside MAX1916, and once Vbat falls below
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	245 this point, the LED current will begin to decline. However, the beauty of this
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	246 design is that no arbitrary artificial turnover points (like the 3.5 V point in
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	247 our hacky design from the spring of 2020) need to be set: the battery discharge
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	248 point at which the LED current begins to decline will be whatever it comes to be
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	249 naturally, based on Vf (perhaps depending on temperature) and MAX1916 Vds, and
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	250 the decline is expected to be gradual.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	251
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	252 1.4.4.1. Backlight current selection and dimming
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	253
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	254 In the simplest MAX1916-based design, a fixed LED current is set by connecting
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	255 a resistor of appropriately computed value between MAX1916 SET pin and whatever
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	256 regulated fixed voltage rail happens to be available in the system. However,
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	257 in our application (see section 1.4.3.1) we need at least two different display
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	258 brightness levels, and thus at least two switchable LED currents. At first the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	259 problem seems difficult, but an elegant solution has been found.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	260
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	261 LCD backlight LED current will be selected by way of two Calypso GPIO pins
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	262 configured as outputs, and a 74LVC2G125 dual tristate buffer. Each tristate
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	263 buffer's A input will be tied high, and the two Calypso GPIO outputs will be
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	264 connected to buffer output enable inputs. There will be two resistors with
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	265 different carefully computed values, each connected between one of the two
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	266 tristate buffer outputs and MAX1916 SET pin. One resistor will provide a small
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	267 current, the other will provide a large current, and each of these two currents
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	268 will be switchable on/off by Calypso GPIO signals switching the buffer outputs
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	269 between driving high (2.7-2.8 V) and Hi-Z. Resistor values will be chosen such
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	270 that the sum of both currents will be the 15 mA limit (the current is reckoned
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	271 per LED), whereas the small current alone will be whatever we need for the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	272 battery-saving long-call dimmed mode.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	273
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	274 1.4.5. Slight regression relative to Pirelli DP-L10
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	275
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	276 The actual LCD backlight LED driving circuit inside the Pirelli phone is not
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	277 known, but reverse engineering of Pirelli's firmware followed by experimentation
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	278 reveals that backlight intensity variation is achieved via a form of PWM, using
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	279 Calypso PWL output - although PWL is used in an inverted sense, such that the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	280 backlight intensity increases with more 0s being put out on PWL, as opposed to
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	281 more 1s. Thus regardless of the unknown actual circuit implementation, the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	282 backlight intensity appears to be continuously variable from 1/255 to 255/255,
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	283 which is certainly a much richer control than our crude selection of just 3
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	284 possible LED currents.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	285
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	286 In terms of what Pirelli's fw offers to end users, the backlight intensity in
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	287 the dimmed in-call state is always set to 1/255, without any way to change it,
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	288 whereas the backlight intensity in the active interaction state is selectable
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	289 via a menu among 5 levels; the 5 offered levels turn into 1/255, 64/255,
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	290 128/255, 192/255 and 255/255 in the resulting PWL programming.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	291
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	292 So in terms of both hardware capabilities and end user offering via the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	293 firmware, Pirelli's LCD backlight level control is richer than what we are
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	294 proposing for our FC Libre Dumbphone. However, engineering is all about
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	295 trade-offs and compromises, and in the Mother's opinion, this slight reduction
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	296 in the richness of functionality is sufficiently offset by the efficiency of
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	297 our MAX1916-based approach: aside from the theoretical possibility of a
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	298 switching buck converter, which I've never seen used for LED driving
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	299 applications, our choice of MAX1916 is the most battery-efficient way to drive
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	300 our backlight LEDs. Furthermore, when dimming is effected by switching the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	301 actual regulated LED current, as in our case, as opposed to applying PWM, our
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	302 backlight becomes more resilient to even lower battery voltages.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	303
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	304 Consider what happens when Vbat falls below the point at which the design-
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	305 intended LED current can be maintained - what happens then? If no PWM is
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	306 applied, or if PWM is set to maximum, then display brightness will be whatever
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	307 maximum is possible at this low battery voltage. But if PWM is applied,
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	308 especially very low duty cycles as in the case of Pirelli's dimmed state, then
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	309 the display that has already been dimmed by low Vbat will be further dimmed
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	310 by this aggressive PWM, likely producing an unreadable display at this point.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	311 It may be possible to compensate via extra complexity in the firmware, by
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	312 turning PWM up when Vbat (as measured via Iota MADC) falls too low - but then
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	313 we would be getting really messy, whereas switching the regulated current is so
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	314 much more elegant. With our approach, low-battery-induced dimming in the "full
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	315 brightness" mode will happen at the same discharge point as it would if we had
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	316 used PWM (and set PWM to maximum in this "full brightness" mode), but in the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	317 in-call dimmed state, further dimming due to low Vbat will probably happen at a
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	318 lower discharge point (if Vf decreases with decreasing current), and when it
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	319 does happen, there won't be a combination of both natural and artificially-
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	320 induced reductions, just the natural one.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	321
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	322 Thus based on all of the above considerations, I feel justified in my design
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	323 choice of foregoing PWM control of backlight intensity in favor of fixed current
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	324 switching with much more limited selection.
44 a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	325
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	326 1.5. Main keypad
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	327
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	328 The main keypad on our FC Libre Dumbphone handset will have the following
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	329 21-button arrangement:
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	330
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	331 left soft key ^ right soft key
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	332 <O>
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	333 green call V red power/hang-up
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	334 button button
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	335
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	336 1 2 3
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	337 4 5 6
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	338 7 8 9
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	339 * 0 #
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	340
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	341 The top section above the traditional numeric dial buttons (12) consists of left
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	342 and right soft keys, green and red buttons (classically called SEND/END), and a
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	343 5-way navigation button group (left, right, up, down and center), for a total of
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	344 9 buttons in this section. The red hang-up button is also the hardware power-on
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	345 button; having the same button effect power-off when held down for some time is
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	346 a firmware function.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	347
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	348 This 21-button main keypad arrangement is exactly the same as featured on
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	349 Motorola C1xx and Pirelli DP-L10 phones, on TI's D-Sample development platform,
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	350 and also on many other phones (non-Calypso) from the appropriate era, such as
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	351 Samsung E2232.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	352
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	353 1.5.1. Keypad backlight
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	354
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	355 All traditional phones including Mot C1xx and Pirelli DP-L10 feature keypad
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	356 backlights, hence we need to include one as well. The exact structure of this
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	357 backlight won't be known until we enter the mechanical design phase for the
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	358 actual handset (as opposed to intermediate development boards), which will be
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	359 much later in the project, but the Mother's understanding is that keypad
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	360 backlights are made up of some number of LEDs (2 on Pirelli DP-L10, unknown
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	361 number on Mot C139) and some kind of light diffuser.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	362
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	363 Given the discovery of MAX1916 constant-current-sink LED driver chip (see
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	364 section 1.4.4), the optimal electrical design of the keypad backlight becomes
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	365 clear: use 3 LEDs, and drive them using another MAX1916 chip, separate from the
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	366 one used for the LCD backlight.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	367
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	368 Backlight intensity: neither Mot C139 nor Pirelli DP-L10 provides any way to
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	369 vary keypad backlight intensity, and no such variability is deemed necessary.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	370 In the long-call state when the LCD backlight is dimmed, the keypad backlight
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	371 is fully off. We shall use a fixed LED current setting for our keypad
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	372 backlight, set with a single fixed resistor between the keypad MAX1916 chip's
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	373 SET pin and the V-IO rail, and the actual current value will be determined in a
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	374 much later phase of the project, when we have the actual keypad backlight LEDs
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	375 and a better idea of the mechanical design.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	376
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	377 Backlight color: Mot C139 uses blue LEDs, Pirelli DP-L10 uses white LEDs.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	378 Because blue and white LEDs have very similar electrical characteristics
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	379 (current needed for appropriate brightness, Vf at this current), the choice
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	380 between the two can be made in a much later project phase, based on input from
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	381 other team members who are better at aesthetics.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	382
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	383 1.5.1.1. Comparison with Mot C139 and Pirelli DP-L10
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	384
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	385 Both of these two pre-existing reference phones feature keypad backlights that
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	386 are switched on/off via Iota LEDB; the actual circuit design is unknown.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	387 However, in our design we forego Iota LEDB altogether (it won't be used for
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	388 anything), and use two MAX1916 chips for our LCD and keypad backlights, with
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	389 each chip's on/off control being a Calypso GPIO.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	390
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	391 The actual workings of the LEDB driver or switch inside the Iota chip are a
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	392 mystery. On the one hand it appears to be nothing more than a "dumb" transistor
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	393 on/off switch, no different from an external "digital transistor" (BJT with bias
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	394 resistors) controlled by a Calypso GPIO: a resistor still seems to be required
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	395 for current control, and at least on the Pirelli DP-L10 the keypad backlight
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	396 intensity visibly varies with Vbat ranging over the Li-ion discharge range. But
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	397 on the other hand, LEDB requires the 13 MHz clock to be running, and the light
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	398 goes out when this clock is stopped. Why in the world would any kind of clock
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	399 be required if the circuit is only a transistor on/off switch controlled by a
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	400 static register bit? Other parts of TI's Iota datasheet describe its LEDA, LEDB
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	401 and LEDC as "current drivers" - but in the absence of any way to actually set
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	402 the desired current without depending on Vbat or Vf variations, whatever the
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	403 Iota chip actually provides can't be anything like MAX1916.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	404
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	405 Poorly documented, non-understood mystery hardware is best avoided, hence we are
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	406 not going to use Iota LEDB, and shall only use MAX1916 instead. We also gain a
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	407 functional improvement over Pirelli DP-L10 by using MAX1916: our keypad
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	408 backlight intensity will remain the same over the battery discharge range.
45 9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	409
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	410 1.6. Side buttons
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	411
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	412 In addition to the 21-button main keypad, our FC Libre Dumbphone handset will
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	413 include 3 side buttons: two on the left side, intended for volume up/down
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	414 control, and one on the right side, serving auxiliary functions. This side
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	415 button arrangement is identical to TI's D-Sample and similar to Pirelli DP-L10:
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	416 the only difference between our arrangement (matching D-Sample) and Pirelli's
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	417 is that Pirelli moved the 3rd side button to the left and designated it as the
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	418 camera button. However, we (FreeCalypso) have no interest in ever implementing
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	419 any kind of camera on our phones, hence we are moving the 3rd side button back
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	420 to where it was in TI's original design (on the right), and we will use it for
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	421 purposes of our own invention.
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	422
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	423 The starting point UI code we got from TI does not do anything with the right
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	424 side button (even though this button exists and works on the D-Sample platform
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	425 on which this code was originally developed), hence we have full freedom to
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	426 invent our own uses for it. The following uses are envisioned:
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	427
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	428 * Long press of this button may be our way of turning the hands-free loudspeaker
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	429 on and off, a function that does not exist in the starting point UI code from
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	430 TI.
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	431
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	432 * When the phone is in its normal idle standby operation (not in a call and not
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	433 being poked at by the user, but registered to a GSM network and ready to
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	434 accept incoming calls or SMS), the display will be off. Users often desire
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	435 to check the time and other status (check coverage, see if they missed any
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	436 calls or SMS), which will require pressing any button to turn on the display.
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	437 At that point a 30 s timer kicks in, which will turn the display back off
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	438 after 30 s of inactivity. However, an argument can be made that keeping the
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	439 display on for 30 s if the user only wanted to quickly glance at the time is
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	440 a waste of battery. Here is one proposed solution: we can implement a
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	441 function where a short press of the right side button when the phone is on its
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	442 idle screen will cause the display to turn off immediately and activate the
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	443 keyguard. The user can then press the right side button once to turn on the
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	444 display and look at it, and then press the same button again to turn it back
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	445 off.
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	446
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	447 * When we are in a long call, the LCD backlight does not turn off completely,
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	448 instead it will go dim - but still readable. Any button presses in this state
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	449 are NOT swallowed - they take their regular actions. However, the keypad
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	450 backlight turns off fully in this state, and under certain conditions (like
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	451 out at night) the user may not be able to see the keypad. If a short press
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	452 of the right side button invokes no other action besides switching on full
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	453 display brightness and the keypad backlight, this right side button can be
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	454 found by touch, and thus solve this particular problem case.
46 1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	455
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	456 1.7. Audio routing
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	457
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	458 3 different audio routing modes will be supported on our FC Libre Dumbphone
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	459 handset:
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	460
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	461 * Default mode: there will be a 32 ohm earpiece speaker physically mounted in
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	462 the usual place, on the front bezel above the display, to match up with the
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	463 user's ear in handheld operation. There will also be a microphone toward the
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	464 front bottom of the phone, again in the usual place.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	465
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	466 * Hands-free mode: there will be an 8 ohm loudspeaker physically separate from
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	467 the 32 ohm earpiece speaker, physical location in the handset TBD. In the
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	468 hands-free mode, the downlink audio will be switched from the earpiece speaker
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	469 to the loudspeaker, while the microphone input for the uplink will remain the
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	470 same.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	471
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	472 * There will be a wired analog headset jack with plug insertion detection; when
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	473 a headset is inserted, both audio input and output will be redirected to this
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	474 headset interface.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	475
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	476 1.7.1. Earpiece and loudspeaker separation
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	477
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	478 Most current mainstream phones (in fact, all that I am familiar with) have
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	479 physically separate speaker transducers for the earpiece function (hold up to
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	480 ear to talk) and the loudspeaker+ringer function. The earpiece speaker is a 32
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	481 ohm load, and the loudspeaker is an 8 ohm load. In a Calypso+Iota design, an
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	482 external amplifier chip is needed to drive the 8 ohm loudspeaker, whereas the
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	483 little 32 ohm earpiece speaker can be driven directly by Iota EAR output.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	484
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	485 However, a very different design was implemented by TI on their D-Sample and
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	486 Leonardo boards. They have only one speaker, one of 8 ohm kind, that is
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	487 physically mounted in the position where the earpiece speaker would normally go.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	488 In order to not overwhelm the user's ear in handheld operation, they have
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	489 peculiar circuit wiring where the analog signal from Iota to the loudspeaker
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	490 amplifier goes through different resistor values depending on whether EAR or AUX
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	491 output from Iota is used, and when the EAR output is selected, the high resistor
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	492 values produce attenuation, such that the sound pressure level produced by the
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	493 pressed-to-ear loudspeaker becomes comparable to that produced by a more
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	494 traditional 32 ohm earpiece speaker.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	495
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	496 Furthermore, TI's single speaker design was not limited to their development
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	497 boards. Some years ago I found schematics for some very old LG phone (called
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	498 A316 or B1200, not sure of the correct designation), this phone is from early
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	499 TI era (pre-Calypso, using Ulysse/Nausica/Clara chipset), and it has the same
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	500 arrangement as D-Sample and Leonardo.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	501
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	502 For our own FC Libre Dumbphone, I am going with the separate speakers
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	503 architecture, using physically separate earpiece and loudspeaker transducers.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	504 This architecture feels more native to me, and it will allow for independent
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	505 tuning of the two audio paths. In my defense, all current mainstream phones
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	506 seem to use the same architecture - the other approach with a single loudspeaker
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	507 in the earpiece physical position seems very uncommon.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	508
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	509 1.7.2. Loudspeaker implementation
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	510
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	511 The external amplifier chip for driving the 8 ohm loudspeaker will be TI
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	512 TPA6203A1, copied from Leonardo schematics and proven good on FCDEV3B. On
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	513 FCDEV3B this amplifier is fed with signal from Iota EAR output, but on the final
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	514 handset and on the Venus development board this amplifier will be fed with
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	515 signal from Iota AUX output instead.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	516
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	517 The loudspeaker amplifier has an on/off control by way of a Calypso GPIO; in
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	518 order to save battery, this amplifier needs to be off normally, and only turn on
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	519 when a loudspeaker call is in progress or when a ringtone melody is played.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	520
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	521 1.7.3. Wired analog headset jack
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	522
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	523 The analog headset jack on our FC Libre Dumbphone handset will be of 2.5 mm
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	524 TRRS type, using pinout copied from iWOW DSK. The headset needs to be wired as
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	525 follows:
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	526
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	527 * 32 ohm earpiece speaker connected between Tip and Ring2;
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	528 * electret condenser microphone, positive connected to Ring1;
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	529 * Sleeve is ground, should be needed only for the microphone.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	530
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	531 The advantage of this TRRS headset specification, as opposed to the simpler kind
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	532 with a TRS plug and a common ground for the earpiece and the mic, is that our
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	533 TRRS headset can be driven with either single-ended or differential earpiece
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	534 driver outputs. On the final handset, the wired headset interface will be
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	535 connected to the Iota headset channel (HSMICBIAS, HSMICP, HSO) and thus the
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	536 headset earpiece driver will be single-ended (HSO and GND), but the same headset
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	537 can also be plugged into other FreeCalypso devices in which the jack is wired
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	538 to the main Iota audio channel, with Iota EARP & EARN driving Tip and Ring2 on
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	539 the TRRS headset jack.

FreeCalypso > hg > freecalypso-docs

annotate FC-handset-spec @ 46:1fec0a3f09cc