LCD for handset and 3D printing help needed

Tue May 29 13:22:13 UTC 2018

Can you make a handmade drawing of the spacer right over the page 6 of the
attached document? Just want to make sure that I understand the description
correctly. I can make few samples. The holes for pins should not be a
problem since their location is clearly defined. I generally can do 0.1mm
resolution with acceptable accuracy using PLA. ABS is much more flexible,
but it shrinks a bit, so it is a guessing game for high precision prints,
hence I will need to have a good PLA sample first.

On Mon, May 28, 2018 at 6:04 PM, Mychaela Falconia <
mychaela.falconia at gmail.com> wrote:

> Hello FreeCalypso community,
>
> I've got a little bit of progress on the LCD selection front (finding
> a suitable LCD module for our FC Libre Dumbphone handset), and I am
> soliciting help from the community with getting a small 3D-printed
> plastic part designed and produced.
>
> After many weeks of delay I finally got the custom PCB which I created
> for connecting HaoRan's HT020K1QC36S LCD to one of our FT2232D adapter
> boards in the MCU host bus emulation mode, this custom LCD test board
> has nothing but connectors and resistors on it, and last week I got
> the needed help with populating it - I wasn't comfortable with
> soldering the 0.5 mm pitch FPC connector myself, even with the use of
> a good microscope at my day job - I couldn't tell if I was positioning
> it correctly, and with such fine pitch it's very easy to move it off
> the mark.  But I finally got it done with the help of my friends at
> Technotronix, and was finally able to test this LCD.
>
> Comparing the picture quality of this HaoRan LCD against the other LCD
> for which I made the needed test rig a month and a half ago (Startek
> KD020C-2A with special film modification), I got a surprising result:
> the picture quality is almost exactly the same between the two, both
> are very good, and the perception of one or the other being slightly
> better is subjective.  I find this result surprising for two reasons:
>
> * Startek's LCD is about double the price of HaoRan's, thus during all
> of these many weeks of waiting I assumed that the cheaper LCD from
> HaoRan would be inferior in quality - but it really isn't.  (And it is
> not a Chinese vs. Western issue - both companies are in Shenzhen.)
>
> * HaoRan's LCD is officially made for 6:00 viewing direction according
> to both the datasheet and my communication with the vendor, whereas
> Startek's LCD was originally a 12:00 display subsequently modified
> with some special film for "free viewing angle".  Startek told me that
> their film modification does not change it into a 6:00 display, yet
> the way the two displays look from different angles is very much the
> same.
>
> So which are we going to use in our handset?  At first it would seem
> that the choice is in favor of HaoRan because it's half the price for
> the same picture quality, but then we've got mechanical mounting
> considerations complicating the picture.  My overall plan for the
> mechanical design of the handset as a whole calls for the LCD to be
> mounted with its FPC tail folded under, so that the footprint of the
> entire LCD arrangement projected onto the XY plane equals the
> dimensions of just the LCD module itself, with *no* extra XY plane
> space being taken up outside of this bounding box for the FPC tail or
> the connector or any other extras.
>
> But it appears that HaoRan's LCD was not designed at all for this FPC
> folded-under arrangement, instead it appears to have been designed to
> be used with its FPC tail stretched out.  If one were to mount this
> LCD with its tail folded under, the contacts would end up facing
> toward the top (toward the body of the LCD, not toward the PCB), and
> there are no thin connectors for this unnatural contact direction,
> only 2.0 mm tall ones.  As far as I can tell, the only sensible way to
> use HaoRan's LCD with the mounting arrangement I seek would be to get
> a custom modified version made with a solder-down tail; I asked Ivy
> (HaoRan's saleslady) about it, and she said they can do it, but it
> would require an MOQ of 1000 pcs, costing about $3200 USD - and I
> would rather avoid this large MOQ and cost if we can.
>
> If we were to use HaoRan's LCD as is and mount it with its tail
> stretched out, there would be about 20 mm of dead space inserted
> between the bottom of the LCD module and the top row of the keypad.
> Look at a Pirelli DP-L10 phone and imagine how it would look and feel
> if all of the keypad buttons were shifted downward by about 20 mm from
> where they are now, leaving a giant dead space - not good at all.
>
> But we may be able to do better with Startek's LCD if we can get a
> custom plastic spacer produced in the needed small quantity by 3D
> printing.  Yes, Startek's LCD is significantly more expensive in
> absolute terms, but this cost would only matter in large quantities -
> for the small quantity we need, the cost would be negligible.  Unlike
> HaoRan's, this LCD has its tail contacts in the more natural
> orientation (facing the bottom with the tail folded under), making it
> easier to find a reasonably thin connector.  We also got some extra
> luck with the pin count: Startek's tail has 45 pins (HaoRan's has 36),
> and for this pin count I was able to find a thin connector (1.3 mm
> height above the PCB) that officially accepts both straight and
> tapered FPC ends, unlike Hirose FH33 series which is made in a wide
> range of pin counts, but requires tapered FPC ends which the LCD
> modules in question do not have.
>
> So, what is this plastic spacer which we need to get designed and
> 3D-printed?  Look at the LCD mechanical drawing on page 6 of this
> Startek datasheet:
>
> https://www.freecalypso.org/members/falcon/lcd/KD020C-2A-
> XXX_SPEC_V1.0_1.pdf
>
> The plastic spacer I envision would go between the LCD module and the
> PCB, elevating the LCD above the PCB to make room for the connector
> underneath.  The spacer would need to be in the shape of the Greek
> capital letter Pi (same as Russian capital P), the width from the
> outer edge of one leg to the outer edge of the other leg would need to
> be 38.40 mm (the outer width of the LCD module), the length of each
> leg would need to be about 41 mm, my current working target number for
> the width of the "Pi" frame is 1.7 mm, and the thickness (the resulting
> added height) needs to be 1.5 mm.
>
> There is also one additional complication with the alignment pins.
> There are two plastic pins (1.0 mm diameter, 0.85 mm long) protruding
> from the back of the LCD module, meant to go into matching holes in the
> PCB for alignment.  These plastic pins are located on the back of the
> LCD module along the rim, thus the 3D-printed spacer would need to have
> two matching holes for these pins to go into.  I am also considering
> if we should put similar protruding pins of our own on the bottom of
> our spacer piece, but I am undecided on this one.
>
> Also as noted in the datasheet drawing, these LCD modules come with
> very thin strips (it says 0.1 mm thickness) of double-sticky tape
> along the outer vertical edges of the back of the module, covered with
> protective film on delivery.  My plan is to have our spacer adhere to
> the LCD module by way of this already-provided adhesive plus the two
> alignment pins tightly fitting into perfectly matched holes in our
> 3D-printed piece, and then use another layer of adhesive (to be
> selected much later) to stick the LCD+spacer assembly to the handset
> prototype motherboard, so the resulting motherboard+LCD assembly will
> be relatively solid without any case or enclosure to hold it together.
>
> So, do we have anyone in our community who would be able and willing
> to take on the challenge of designing and 3D-printing this plastic
> spacer?
>
> Hasta la Victoria, Siempre,
> Mychaela aka The Mother
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