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 < [email protected]> 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 > _______________________________________________ > Community mailing list > [email protected] > https://www.freecalypso.org/mailman/listinfo/community > _______________________________________________ Community mailing list [email protected] https://www.freecalypso.org/mailman/listinfo/community
