Author Topic: LCD design, is this good enough?  (Read 7138 times)

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Offline robertbaruch

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LCD design, is this good enough?
« on: February 02, 2019, 10:04:05 am »
Here's an LCD design which is a replacement for the LCD in a 1980 TRS-80 PC-1 Pocket Computer. Many of these have gone bad due to bad seals between the upper and lower glass, so I'm thinking I could make 100-200 of these and fix every PC-1 in existence :) I measured the (dead) one that I have and found the electrical specifications in the service manual.

The file is in PDF, but I also have an SVG file.

The only think I haven't specified is the font, so I converted the text to SVG paths and hopefully the Chinese manufacturers will be able to produce a mask from that.

What do you think? Is this a good enough spec sheet for someone in China?
 
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Offline robertbaruch

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Re: LCD design, is this good enough?
« Reply #1 on: February 04, 2019, 05:59:54 am »
So I guess this is going to be a project log about getting this thing made. I really don't want to spend more than about $500 total on this project excluding the samples. For a U.S. factory that would be a nonstarter, but let's see what happens with China.

I went to Alibaba and searched for "custom lcd display". I chose three suppliers that had pictures showing LCDs that weren't big LCD displays, that had "gold supplier" status and over three years in business, and sent this message, patterned after this article:

Quote
Hello,

My name is Robert Baruch and I am searching for a reliable supplier of custom LCDs. I came across your company in my research and wanted to get some further information regarding your minimum order quantities and FOB pricing for a 24x1 character LCD with nine indicators. Please see the attached PDF for specifications.

So could you please get back to me as soon as possible with the above information? My email is robert.c.baruch@gmail.com

Thank you and I look forward to hearing from you and hopefully placing an order with your company.

Kind regards,
Robert Baruch
(Mountain View, California, USA)


I know, it seems overly formal but we're dealing with a language barrier here. Messages were sent on 2 Feb, however the Lunar New Year is coming up, so I didn't really expect much in the way of replies. Nevertheless...

Supplier A, with 11 years in business, responded with "I don't understand your diagram. Do you have specs?" I sent a polite "We're going with another supplier" message.

Supplier B responded say they were on vacation until 18 Feb.

Supplier C responded with good feedback:
  • The glass should be 1.1 mm (1.0 is not standard, apparently the standards are 0.4, 0.55, 0.7, 1.1 mm).
  • They misunderstood my diagram as wanting white on black, which is negative display, not positive display.
  • The MOQ is 2400
I responded saying 1.1 mm would be fine, I really wanted black on white, and that the MOQ is fine, but I'd like to know the price.

I changed a few things based on supplier C's feedback, here's the latest revision.
 

Offline robertbaruch

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Re: LCD design, is this good enough? (project log)
« Reply #2 on: February 04, 2019, 06:12:58 am »
Oh, here's an image, since you probably don't want to bother with a PDF! This was drawn in Inkscape.

 

Offline robertbaruch

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Re: LCD design, is this good enough?
« Reply #3 on: February 04, 2019, 06:20:51 am »
Here's an image (ebay) of typical LCD degradation on these things.

 

Offline Benta

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Re: LCD design, is this good enough?
« Reply #4 on: February 04, 2019, 06:26:52 am »
I doubt if you'll get any joy from your specification.
I strongly suspect that the manufacturer wants a graphic layout of the front plane and the back plane of the LCD (like a top side and bottom side copper Gerber for PCBs).
Just showing the pixel placement and routing is far too much bother for the manufacturer for this kind of volume.
Ask the manuf. what kind of design files are needed, odds are Gerbers could be OK.
 

Online SiliconWizard

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Re: LCD design, is this good enough?
« Reply #5 on: February 04, 2019, 06:30:12 am »
You could ask Dave (Jones), as he's had a custom LCD made for his last project and may have a few tips. I think he had a contrast issue on the first batch IIRC, so expect maybe two or more rounds before getting it right.

 

Offline robertbaruch

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Re: LCD design, is this good enough?
« Reply #6 on: February 04, 2019, 06:41:14 am »
Quote
I strongly suspect that the manufacturer wants a graphic layout of the front plane and the back plane of the LCD (like a top side and bottom side copper Gerber for PCBs).

Oh, interesting -- I could probably do that also. I didn't because Dave's video didn't show that. If it would save on the price, I could do it myself...
 

Offline HwAoRrDk

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Re: LCD design, is this good enough?
« Reply #7 on: February 04, 2019, 05:24:11 pm »
Do you plan to make any videos about this project?

Been enjoying your Battlezone repair series so far. :)
 

Offline robertbaruch

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Re: LCD design, is this good enough?
« Reply #8 on: February 05, 2019, 12:40:14 pm »
I dunno, there's not much video potential here, is there? Maybe I could get StrangeParts to take a tour of an LCD factory :)
 

Offline robertbaruch

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Re: LCD design, is this good enough?
« Reply #9 on: February 05, 2019, 01:33:07 pm »
Supplier C responded with a quote, USD 200 per tooling (so if I screw up and need a fix, I pay another 200) and USD 1.15 each for 2400. That's a lot more than I'm willing to pay. Interestingly, their quote specified 1.1mm glass, with a total thickness of 2.8mm max. Not sure where that extra 0.7mm came from. The original is 2mm thick total with 1.0 mm glass. Anyway, I'll be sending them a polite note saying that I'm going with another supplier.

I can see that small orders is not what Supplier C is going for. Thing is, I'd still be willing to pay $500 if their MOQ were 100. I need to find maybe a smaller supplier that's willing to do small orders. If that's even possible.

Also I'll be providing gerbers as well as the design PDF, maybe that will help.
« Last Edit: February 05, 2019, 01:39:45 pm by robertbaruch »
 

Offline robertbaruch

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Re: LCD design, is this good enough?
« Reply #10 on: February 05, 2019, 04:00:34 pm »
How would I represent these things in the gerber files? They look like some kind of metallic paste. They are effectively vias between top and bottom glass.

 

Offline robertbaruch

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Re: LCD design, is this good enough?
« Reply #11 on: February 06, 2019, 09:52:20 am »
Here's something I whipped up in KiCAD. Hopefully the gerbers from this file should be good enough for a manufacturer to use. I used the trace width from the original LCD (0.35mm) and the same for spacing. Yellow dots are whatever the equivalent of vias are for LCDs.

The actual display area where the liquid crystal goes is just a box around the matrices and indicators, so the crossings at the top don't actually form segments.

« Last Edit: February 06, 2019, 09:55:13 am by robertbaruch »
 

Offline james_s

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Re: LCD design, is this good enough?
« Reply #12 on: February 06, 2019, 12:49:29 pm »
This is an interesting project, it has never occurred to me that this sort of thing could even be done.

You might ask about prices on a smaller run, you might also try a kickstarter or similar campaign to get funds. I don't know how much demand there is for these displays, I personally have no use for one but it would be fascinating to see this project succeed.
 

Offline Benta

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Re: LCD design, is this good enough?
« Reply #13 on: February 07, 2019, 03:32:33 am »
Check with the manufacturer if he has another solution than the vias. I've seen LCDs where the traces are brought to the edge of the glass and a connection between front plane and back plane made. This would be much cheaper.

 

Offline robertbaruch

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Re: LCD design, is this good enough?
« Reply #14 on: February 17, 2019, 06:12:01 am »
Hooray, the Chinese holiday is over.

Supplier B responded, with an MOQ of 3000. This time I replied asking for an MOQ of 200, and they replied saying 200 was the same as asking for samples, and there would be no profit in it. Then they asked what my target price was, and I replied USD 500 not including samples or tooling.

I'm not sure whether they took that to mean USD 500.00 per piece, or USD 5.00 per piece, or USD 2.50 per piece (my bad, I should be more explicit). But then they asked some followup questions:

  • Is this TN or HTN? (TN).
  • Is this an LCD or LCM? (LCD).
  • Do they need to provide the elastomeric strip (no, I hope this doesn't come back to bite me).

They asked if I had a sample, I provided images. I also said that the USD 500- was for 200, so USD 2.50 per piece.

Supplier D replied with MOQ 1000 "with repeat order expected". I replied with my apologies and that my budget was limited to USD 500 not including tooling and samples.

I have the awful feeling that LCDs are never going to be within reach of the hobbyist. Part of the process is similar to PCB manufacture, but it seems the rest of the process is not high-volume enough to turn the industry into something like the PCB industry.
 

Offline amyk

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Re: LCD design, is this good enough?
« Reply #15 on: February 17, 2019, 06:34:40 am »
Supplier C responded with a quote, USD 200 per tooling (so if I screw up and need a fix, I pay another 200) and USD 1.15 each for 2400. That's a lot more than I'm willing to pay. Interestingly, their quote specified 1.1mm glass, with a total thickness of 2.8mm max. Not sure where that extra 0.7mm came from. The original is 2mm thick total with 1.0 mm glass. Anyway, I'll be sending them a polite note saying that I'm going with another supplier.

I can see that small orders is not what Supplier C is going for. Thing is, I'd still be willing to pay $500 if their MOQ were 100. I need to find maybe a smaller supplier that's willing to do small orders. If that's even possible.
Sorry to say this, but that is already very cheap for a custom LCD. $1K+ tooling is not uncommon. As for the thickness, they may not be able to source the materials for what you're asking for.
 

Offline robertbaruch

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Re: LCD design, is this good enough?
« Reply #16 on: February 19, 2019, 05:21:20 am »
Supplier B replied, saying that I really wanted STN rather than TN, I said that was fine. They also were willing to meet my price of USD 2.50/pc at 200 pcs. The "mould" fee would be USD 320. This is definitely within my budget!

I'm actually surprised that they were willing to work with me on this. There can't be much profit in this order. On the other hand, they've apparently been in business for only 2 years so maybe they're more amenable to small orders.  :-// Maybe it helped that I gave them gerbers so that they don't have to do any design work. More fool me if I made a mistake in the gerbers.

On a separate track, I thought I'd also explore what it takes to build one yourself. I see that you can get ITO-coated glass from China, which already is an improvement over having to go the Ben Krasnow route of doing your own sputtering (he later just got the ITO-coated glass from ebay as well). I've also been clued in to PEDOT:PSS which is apparently a more friendly version of ITO, but given that I can short-cut the experimentation with just getting ITO glass, I don't really want to experiment with PEDOT:PSS unless I have to.

The next steps would be to see how precisely I can cut the glass into the rectangles required, and how to etch away the ITO with a 0.35mm trace/space. Interestingly, 0.35mm is just about 72dpi, which is was "video resolution" or "screen resolution" back when we had CRTs. Coincidence? The original LCD displays I'm reproducing were from the early 80's.

I haven't done photochemical etching for decades, and my experience was pretty sad (basically laser printing onto a transparency, and tripling up the transparencies to get adequate opacity).
 
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Offline robertbaruch

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Re: LCD design, is this good enough?
« Reply #17 on: February 23, 2019, 07:22:30 am »
Today's update!

Supplier B sent a proforma invoice for USD 320, plus USD 36 shipping, and USD 14 handling. This covers the re-drawing, tooling, and 10 sample pieces shipped in a styrofoam box. The next step is payment (via Alibaba), then they re-draw, send it to me for approval, and when I confirm (or all changes are done), then they'll produce the 10 samples and ship. They said I would receive the samples 20-25 working days after sign-off of the final drawing.

Still haven't received the bare ITO glass to experiment with, it will take a while. In the meantime I can probably look into what chemicals I'll need to make a photosensitive layer on glass. (Thoughts?)
 

Offline robertbaruch

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Re: LCD design, is this good enough?
« Reply #18 on: February 25, 2019, 07:02:49 pm »
about the LCD that I'm making.
 
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Offline TiN

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Re: LCD design, is this good enough?
« Reply #19 on: February 26, 2019, 03:59:47 pm »
Thanks for creating this thread, interesting indeed.
YouTube | Chat room | Live-cam | Have documentation to share? Upload here! No size limit, firmware dumps, photos.
 

Offline gearedbyby

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Re: LCD design, is this good enough?
« Reply #20 on: February 26, 2019, 08:44:05 pm »
it's a old boy,good luck ;D
 
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Offline TERRA Operative

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Re: LCD design, is this good enough?
« Reply #21 on: February 26, 2019, 09:03:50 pm »
Interesting thread. Maybe someone can follow in your footsteps to get new LCD's for all the old HP benchtop multimeters. :D
Any circuit design must contain at least one part which is obsolete, two parts which are unobtainable, and three parts which are still under development.

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Offline robertbaruch

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Re: LCD design, is this good enough?
« Reply #22 on: March 01, 2019, 03:30:29 pm »
Supplier B sent back detailed drawings, 5 pages.

First page: Overall dimensions, pin pitches, pin positions, and electrical/optical data. There is an inset box asking for the best display angle. Where 90 degrees is vertical (i.e. looking straight down at the display), they give a choice between 80, 60, and 40 degrees. My angle would be 60 degrees.

I note that there is also a bump of some kind on the left side for what appears to be sealing. The original LCD also has a hard black bump, but on the right side. I don't think this should make much of a difference, but I am going to ask that it be moved to the other side anyway.

Second page: Segment designators, and dimensions for 5x7 matrices.

Third page: Two diagrams, the first showing segment connections to pins, the second showing common connections to pins.

Fourth page: A matrix showing COM0-COM7 on the Y axis, and pins 1-144 on the X axis.

Fifth page: "The Display Effect", showing an overall drawing.

All is correct, with the exception of the bump on the side. Also, the lettering on the indicators is not great. They did specify the indicator height correctly, but appear to have ignored the table I included for where their left sides are and how long they are. I gave them that feedback, asking them to use the table, and also I gave them a TTF font file they can use (it's DejaVu Sans, so it's free). That and any vector editor should get them to the right look.

I'm attaching the PDF they sent me -- if you're interested, just download it. Don't want to go through the bother of converting to images :)
 
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Offline robertbaruch

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Re: LCD design, is this good enough?
« Reply #23 on: March 03, 2019, 06:40:15 am »
Supplier B (may as well call them DDX Electronics) sent back new drawings (attached). This seems to solve the font problem, moves the bump to the right side (yay!) and also shows the viewing angle at 60 degrees.

However, the lettering is in the wrong place. They are approximate, but not according to spec. I suspect the engineer just eyeballed it. It's important to get this right, because retro restoration.

I sent back an email explaining this, and showing an example of the SHFT indicator, with calculations showing that the left edge must be 0.2 mm left of the left edge of segment 2AH, where the diagram they sent shows it on the right of 2AH. I also sent a drawing with a table. Hopefully this makes it easier for them.

*edited to use attachment as inline image

« Last Edit: March 04, 2019, 05:47:23 am by robertbaruch »
 
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Offline Benta

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Re: LCD design, is this good enough?
« Reply #24 on: March 03, 2019, 07:13:19 am »
I'm immensely impressed with the efforts you've put into this project and the results achieved so far.
Please keep us updated.

All the best.
 
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