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FC-handset-spec: KWH020ST23-F01 finalized
author Mychaela Falconia <falcon@freecalypso.org>
date Thu, 16 Sep 2021 00:08:00 +0000
parents c6dafe9f3ac2
children e4eebf9ffce3
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72:2ac10b2cde4f 73:eb68975e1b81
89 physical size, with 31.68x39.60 mm active area and 0.180 mm dot pitch, hence 89 physical size, with 31.68x39.60 mm active area and 0.180 mm dot pitch, hence
90 this physical size is the one we are going to use. 90 this physical size is the one we are going to use.
91 91
92 1.4.2. Specific LCD module selection 92 1.4.2. Specific LCD module selection
93 93
94 As of 2021-07, the frontrunner candidate LCD module for our FC handset is 94 Over the summer of 2021 we have selected Formike KWH020ST23-F01 as our LCD
95 Formike KWH020ST23-F01. Our selection criteria are as follows: 95 module for FreeCalypso; in prior years we had evaluated two other LCD modules
96 from HaoRan and Startek. All relevant datasheets (our finally chosen LCD
97 module, our previous candidate LCD modules and the controller ICs inside these
98 modules) are collected here:
99
100 ftp://ftp.freecalypso.org/pub/embedded/LCDs/
101
102 Our LCD module selection criteria were as follows:
96 103
97 * TFT color LCD, 2.0" diagonal, 176x220 pixel resolution; 104 * TFT color LCD, 2.0" diagonal, 176x220 pixel resolution;
98 105
99 * 16-bit microprocessor bus interface; 106 * 16-bit microprocessor bus interface;
100 107
114 naturally from the target application (cellular phone handset), and the 121 naturally from the target application (cellular phone handset), and the
115 backlight LED wiring requirement stems from the constraints of our chosen 122 backlight LED wiring requirement stems from the constraints of our chosen
116 MAX1916 backlight LED driver chip - see section 1.4.4. 123 MAX1916 backlight LED driver chip - see section 1.4.4.
117 124
118 Formike KWH020ST23-F01 is an LCD module that was discovered by Mother Mychaela 125 Formike KWH020ST23-F01 is an LCD module that was discovered by Mother Mychaela
119 in May-June of 2021, and it appears to satisfy all of our requirements. We have 126 in May-June of 2021, and it satisfies all of our requirements. In June of 2021
120 designed a test board for the purpose of evaluating this LCD (it will connect 127 we received sample pieces, then we designed a test board for the purpose of
121 the new LCD to our Luna interface from 2020), but because of Digi-Key part 128 evaluating this new LCD, connecting it to our Luna interface from 2020. Our
122 backorder issues, the assembly of this board and thus the actual test are being 129 lunalcd2 test board was finally assembled in August, all tests passed, and as
123 delayed until Sep-Oct of 2021. 130 of September we are in process of ordering a larger batch of these finally
131 chosen Formike LCD modules.
124 132
125 1.4.3. Backlight and readability considerations 133 1.4.3. Backlight and readability considerations
126 134
127 Out of the various pre-existing mobile phones which I (Mychaela) have 135 Out of the various pre-existing mobile phones which I (Mychaela) have
128 experienced, there have been 3 different kinds of LCDs in terms of how display 136 experienced, there have been 3 different kinds of LCDs in terms of how display
192 implementation will allow a total of 4 different backlight intensity levels - 200 implementation will allow a total of 4 different backlight intensity levels -
193 see section 1.4.4.1. 201 see section 1.4.4.1.
194 202
195 1.4.4. Backlight circuit implementation 203 1.4.4. Backlight circuit implementation
196 204
197 In all candidate TFT LCD modules that are being considered (see section 1.4.2), 205 In all candidate TFT LCD modules that have been considered (see section 1.4.2),
198 the backlight consists of 3 white LEDs wired in parallel, joined either at the 206 the backlight consists of 3 white LEDs wired in parallel, joined either at the
199 anode or at the cathode - although as we shall see momentarily, we require an 207 anode or at the cathode - although as we shall see momentarily, we require an
200 LCD module where the 3 LEDs are joined at the anode, with the 3 cathodes brought 208 LCD module where the 3 LEDs are joined at the anode, with the 3 cathodes brought
201 out separately. LCD module datasheets call for 15 mA current through each LED 209 out separately. LCD module datasheets call for 15 mA current through each LED
202 at maximum intensity, for 45 mA total, and the LED forward drop voltage (Vf) at 210 at maximum intensity, for 45 mA total, and the LED forward drop voltage (Vf) at
283 contribution currents will equal the 15 mA limit - the current is reckoned per 291 contribution currents will equal the 15 mA limit - the current is reckoned per
284 LED. The difference between the 15 mA maximum and the small dimmed mode current 292 LED. The difference between the 15 mA maximum and the small dimmed mode current
285 will be split unequally between the two switched SET resistors, allowing a total 293 will be split unequally between the two switched SET resistors, allowing a total
286 of 4 different backlight intensity levels to be selected via the two Calypso 294 of 4 different backlight intensity levels to be selected via the two Calypso
287 GPIO outputs going to the 74LVC2G125 buffer's output enable inputs. The actual 295 GPIO outputs going to the 74LVC2G125 buffer's output enable inputs. The actual
288 currents will be determined some time around Sep-Oct of 2021 when we get our 296 currents will be determined after some further experimentation with our lunalcd2
289 lunalcd2 test board built. 297 test setup: this setup features our KWH020ST23-F01 LCD, a MAX1916-based
298 backlight circuit, and a DIP switch pack selecting the LED current in 1 mA
299 increments.
290 300
291 1.4.5. Slight regression relative to Pirelli DP-L10 301 1.4.5. Slight regression relative to Pirelli DP-L10
292 302
293 The actual LCD backlight LED driving circuit inside the Pirelli phone is not 303 The actual LCD backlight LED driving circuit inside the Pirelli phone is not
294 known, but reverse engineering of Pirelli's firmware followed by experimentation 304 known, but reverse engineering of Pirelli's firmware followed by experimentation