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 _______________________________________________ Community mailing list Community@freecalypso.org https://www.freecalypso.org/mailman/listinfo/community