Author Topic: LCD design, is this good enough? (Read 25010 times)

robertbaruch · « **on:** February 01, 2019, 11:04:05 pm »

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?

robertbaruch · « **Reply #1 on:** February 03, 2019, 06:59:54 pm »

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.

robertbaruch · « **Reply #2 on:** February 03, 2019, 07:12:58 pm »

Oh, here's an image, since you probably don't want to bother with a PDF! This was drawn in Inkscape.

robertbaruch · « **Reply #3 on:** February 03, 2019, 07:20:51 pm »

Here's an image (ebay) of typical LCD degradation on these things.

Benta · « **Reply #4 on:** February 03, 2019, 07:26:52 pm »

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.

SiliconWizard · « **Reply #5 on:** February 03, 2019, 07:30:12 pm »

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.

robertbaruch · « **Reply #6 on:** February 03, 2019, 07:41:14 pm »

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...

HwAoRrDk · « **Reply #7 on:** February 04, 2019, 06:24:11 am »

Do you plan to make any videos about this project?

Been enjoying your Battlezone repair series so far.

robertbaruch · « **Reply #8 on:** February 05, 2019, 01:40:14 am »

I dunno, there's not much video potential here, is there? Maybe I could get StrangeParts to take a tour of an LCD factory

robertbaruch · « **Reply #9 on:** February 05, 2019, 02:33:07 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.

Also I'll be providing gerbers as well as the design PDF, maybe that will help.

robertbaruch · « **Reply #10 on:** February 05, 2019, 05:00:34 am »

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.

robertbaruch · « **Reply #11 on:** February 05, 2019, 10:52:20 pm »

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.

james_s · « **Reply #12 on:** February 06, 2019, 01:49:29 am »

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.

Benta · « **Reply #13 on:** February 06, 2019, 04:32:33 pm »

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.

robertbaruch · « **Reply #14 on:** February 16, 2019, 07:12:01 pm »

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.

amyk · « **Reply #15 on:** February 16, 2019, 07:34:40 pm »

Quote from: robertbaruch on February 05, 2019, 02:33:07 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.

robertbaruch · « **Reply #16 on:** February 18, 2019, 06:21:20 pm »

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).

robertbaruch · « **Reply #17 on:** February 22, 2019, 08:22:30 pm »

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?)

robertbaruch · « **Reply #18 on:** February 25, 2019, 08:02:49 am »

about the LCD that I'm making.

TiN · « **Reply #19 on:** February 26, 2019, 04:59:47 am »

Thanks for creating this thread, interesting indeed.

gearedbyby · « **Reply #20 on:** February 26, 2019, 09:44:05 am »

it's a old boy,good luck

TERRA Operative · « **Reply #21 on:** February 26, 2019, 10:03:50 am »

Interesting thread. Maybe someone can follow in your footsteps to get new LCD's for all the old HP benchtop multimeters.

robertbaruch · « **Reply #22 on:** March 01, 2019, 04:30:29 am »

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

robertbaruch · « **Reply #23 on:** March 02, 2019, 07:40:15 pm »

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

Benta · « **Reply #24 on:** March 02, 2019, 08:13:19 pm »

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.

oPossum · « **Reply #25 on:** March 02, 2019, 10:27:57 pm »

Quote from: robertbaruch on March 02, 2019, 07:40:15 pm

(BTW, is there any way to have an inline image where the image is an attachment rather than a link to imgur which can go away at any moment?)

It is a two step process. Make the post with attached images, and then edit it to use the attachment URLs for inline images.

robertbaruch · « **Reply #26 on:** March 02, 2019, 11:10:23 pm »

I also asked to change the operating voltage from 5.2V to 2.6V. I mistakenly thought that applying an AC waveform between -2.6 and +2.6 would result in an operation voltage of 5.2V, but it is actually 2.6V -- the segment is on at 2.6V, but you flip the polarity.

kony · « **Reply #27 on:** March 02, 2019, 11:18:43 pm »

Word of advice - if someone dun fucked up something mechanical, yet provided proper 2D drawing for reference, always do the corrections graphically as overlay (or better yet in DXF if the original is provided) with marked and updated values of wrong dimensions and added new ones. Especially if there is languague barrier. Text directions can be ambiguous, and much harder to navigate.

Refrigerator · « **Reply #28 on:** March 02, 2019, 11:28:55 pm »

Oh boy, this thread is some good stuff.

wrickert · « **Reply #29 on:** March 03, 2019, 06:12:27 pm »

That is a great idea. I have been playing with the idea of a smartwatch as a conference badge. I have been struggling to find a cheap display for cheap enough. This might be the perfect solution. I can't wait to hear more.

robertbaruch · « **Reply #30 on:** March 03, 2019, 06:48:25 pm »

Quote from: oPossum on March 02, 2019, 10:27:57 pm

It is a two step process. Make the post with attached images, and then edit it to use the attachment URLs for inline images.

Works, thanks!!!

ebastler · « **Reply #31 on:** March 03, 2019, 08:35:11 pm »

Great to see how you are following through with this, Robert!

But I am also impressed by the professional support provided by your "supplier B", DDX. You are getting good value for your 320$ tooling and NRE fee. If the final product is as convincing as the dialog to plan and specify it, the result should be really neat!

Quote from: robertbaruch on February 18, 2019, 06:21:20 pm

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!

robertbaruch · « **Reply #32 on:** March 06, 2019, 02:17:23 am »

Last round of changes are in, and it's looking good! I signed the first page and sent it back, and now we wait 4-6 weeks for the samples!

I have learned:

1. Sending a multi-page spec is better than a single page.
2. Using a matrix for the pins instead of a pinout is apparently standard for LCDs.
3. Don't spell anything else out in tables. Put all the measurements on the drawings.

james_s · « **Reply #33 on:** March 09, 2019, 03:54:09 am »

Even if the final product is junk, there's probably $320 worth of education in this thread. Prior to this I had no idea custom LCDs were even remotely feasible in volumes less than tens of thousands.

krasin · « **Reply #34 on:** March 09, 2019, 04:22:23 am »

This. I am surprised that getting a custom LCD is projected to be cheaper than a custom injected molded case.

I really hope this project succeeds and the experience is documented, so that others can follow.

robertbaruch · « **Reply #35 on:** March 26, 2019, 02:37:13 am »

Thought I'd post a description and pic of the test jig I'm going to use for testing the LCD samples. First, I'm just going to set up a simple square wave and test one segment, see what the threshold is, that sort of thing. Then I'm going to use this jig, which has 144 pogo pins on it. The pogo pins are 0.65mm in diameter, and the tips are rounded. I did check to see if the tips would scratch the LCD pads on my dead LCD, and they didn't seem to do any damage! Finally, I'll test one of the LCDs in a real TRS-80 PC-1.

Why pogo pins and not an elastomeric strip? Well, I don't have any extra elastomeric strips, and I don't find them easy to use. They're a bit fiddly.

So I 3D printed this holder for the pogo pins, and I have two circuit boards. One is a more general driver, and the other is the adapter for the specific LCD.

The general driver uses a single PCF8545B LCD driver from NXP. This driver is "universal", being capable of up to 8 commons and up to 40 rows (i.e. 320 segments), with driving voltages from 1.8 to 5.5v, biasing of 1/2, 1/3, or 1/4, multiplexing of 1:4, 1:6, or 1:8, and a range of scan frequencies from 60-300Hz, AND two types of output waveforms.

Sounds awesome, right? Well, sadly, unlike a lot of their other chips, this one is not cascadable, meaning you can't add rows. If you wanted to add rows, you'd have to make sure the chips are synced in their commons, and that's what cascadable chips can do. Not this one, so you can't just use four of them, their commons wouldn't sync. Sadly, NXP does not make a chip with 8 commons that is cascadable. If you happen to know of one, let me know!

So instead, I'm resigned to testing only one portion of the LCD at a time. My LCD has 4 "sections": 3 sections of 40 rows for the character display, and 1 section of 9 rows for the indicators. I connect a FSAL200 quad analog multiplexer to each row, and I set up the test jig to have 4 sections of 40 rows. That's 160 rows, but 40 quad multiplexers. The multiplexers switch either the signal from the LCD driver, or 1/2 the LCD voltage, which is the "off" state of a segment. In this way, I can switch the LCD driver to drive any one of the 4 sections of 40 rows.

The whole thing is controlled with, of course, an Arduino (Pro Mini, 5V). There are four buttons, a bunch of LEDs, and a 4-digit 7-segment display. With that, I can program the LCD driver to the right bias, LCD voltage, multiplexing, waveform, and frequency, and then step through the sections to test. I decided to use a DAC instead of a low-pass filter on the Arduino's PWM output because I wanted a more stable voltage.

Anyway, the factory says they'll have the samples ready by the end of the month, and theoretically it will take 1-2 weeks after that to get here.

In other news, I attempted to set up a CrowdSupply crowd-sourcing campaign. You have to fill out a form with all the details of your project, how much you want to crowdfund, what you're going to spend it on, and so on. I think it's a higher bar than Kickstarter or IndieGoGo. Reasonable fees, too, and they handle fulfilment. However, that was two weeks ago, and they claim to get back to you in a week. So... I don't know how that's going to turn out. I do want to set up a crowdfunder for this.

robertbaruch · « **Reply #36 on:** April 07, 2019, 07:00:17 pm »

I have the sample LCDs! Running my fingers along the contacts (grounding one of the commons) shows all the segments seem good and in the right place. The size is also correct.

There's just one problem. The PCF8545 LCD driver doesn't seem to be behaving as expected. I can program it via SPI, no problem. The common pins ("BP", or "backplane" in the datasheet) have the correct waveform. However, the segment pins don't behave! They are supposed to vary between 0v, 1/2 VLCD, and VLCD. In fact, at VLCD = 2.5, they vary between 0v, 3.3v, and 2.5v. Yes, every time the segments are supposed to be at 1/2 VLCD, they go to 3.3v!

This is a problem because there are protective diodes going from the segment outputs to VLCD, so they conduct! And yes, the chip gets hot!

I changed VLCD to 4.0v, but now the chip outputs 4.6v when it should be at 1/2 VLCD. So we have a situation where segments at 1/2 VLCD result in an output of 0.6-0.8 volts above VLCD. It's suspicious.

I'd ask NXP what's going on, but historically they have never answered a question about any of their PCF85xx chips.

There was a suggestion on Twitter that maybe NXP reversed the pins on VLCD and VCC.

robertbaruch · « **Reply #37 on:** April 07, 2019, 11:09:22 pm »

Without a functioning LCD tester, I just decided to go for broke and install a new LCD into a known working Sharp PC-1211 (aka TRS-80 PC-1). It works! At least, all the segments are active. However, I need to adjust the contrast. If that doesn't work, then I'm pretty sure that the threshold voltage is incorrect. I can see that when I press the mode switch, the mode segments do change slightly.

robertbaruch · « **Reply #38 on:** April 07, 2019, 11:49:09 pm »

And it turns out that for the PCF8545 driver, VLCD must be greater than VCC, which cannot be done here.

So back to the drawing board for an LCD tester.

robertbaruch · « **Reply #39 on:** April 08, 2019, 12:31:47 am »

I damaged the wiper on the contrast pot because it was all painted down. So with the wiper removed (pot at max resistance) I just decided to see what the display looked like.

So close! Those last few matrices have something odd going on with them. I'm tempted to call it flaw in the LCD manufacture, but I really need to replace a second one to see if the effect is replicated.

Refrigerator · « **Reply #40 on:** April 08, 2019, 07:59:02 pm »

awesome stuff, these sharps seem quite prone to LCD failures.

robertbaruch · « **Reply #41 on:** April 09, 2019, 04:16:08 am »

I opened the thing back up, placed a paper shim in the bezel to make sure the LCD didn't move from where I thought it should be, cleaned the pads and the elastomeric strips with alcohol, made sure not to touch them, put them in place, and buttoned it all up again. And....

A qualified success! Qualified because (a) I still need to reproducibly replace an LCD without several tries, and (b) you have to replace the contrast adjustment with a 240k resistor.

What's interesting is that on the original, the LCD was placed into the bezel with an adhesive strip, so once it was in the bezel, you couldn't move it. And the original LCD does have a little play in the bezel. I'll have to look more closely at an original to see if they glued the LCD in the same place as I put it.

barbeque · « **Reply #42 on:** April 09, 2019, 01:30:07 pm »

Congratulations! That looks amazing.

I would have been tempted to slip in an easter egg in the "mode" line. I remember as a kid holding a lot of LCDs up to bright lights to see what modes I haven't managed to enable yet/weren't offered on my model.

HwAoRrDk · « **Reply #43 on:** April 09, 2019, 03:52:41 pm »

Looks great. As Dave would say: "Like a bought one!"

robertbaruch · « **Reply #44 on:** April 14, 2019, 04:01:47 am »

Final video! I put this one up on diode.zone first -- I want to support a non-YouTube video streaming instance.

coromonadalix · « **Reply #45 on:** April 14, 2019, 02:46:28 pm »

Man Impressive work

Has others wrote, some HP Agilent stuff could / can be saved with guidance like this.

Keatah · « **Reply #46 on:** April 28, 2019, 07:21:08 am »

This is really really great news! I have 11 PC-1 units between myself and friends that could use such a replacement! And I wouldn't mind paying about $25 - $30 per display (if that's a fair cost and allows for some personal profit)..

I was almost almost getting ready to cannibalize other units to make 1 working. But now with this project that may not be necessary.

Can you please update us on how this is coming along and if and when some will be available?

---

I got to thinking and wondering if it's possible to specify a more yellow-tinted color instead of the grey/green shown in the videos? For authenticity.. Or might it be as simple as retaining the yellow filter already present?

I also believe there are more than just a couple hundred of these pocket computers out there. I see one or two move for between $30 and $100 per month.

But there's a lot of delicate work involved in the repair. And watching your second video is going to be required. If any obstacle to selling these replacement displays exists it is that and likely not the amount of units out there. And the ones that are still working are likely to fail sooner or later.

robertbaruch · « **Reply #47 on:** April 28, 2019, 06:50:17 pm »

I've ordered the run of 200 from the manufacturer, and that should hopefully arrive by the end of May. At that point I'll put up a shop on Tindie and start selling them. I did apply to get CrowdSupply to make this a crowd-sourcing project rather than just a store, but CrowdSupply really dropped the ball on this one.

It's not likely that I'll meet my goal of 2.5x the cost. I probably can't put two of the same thing on Tindie, one for, say, $20, and the other for $40 ($20 for the LCD plus $20 support).

I've found that there are some of the PC-1/PC-1211 that can't be fixed by just replacing the LCD -- there's something more fundamental going on, so an LCD swap isn't a guaranteed fix for *everything*

trompczynski · « **Reply #48 on:** May 17, 2019, 02:26:03 am »

Just came across this when searching alternatives for my PC-1211 once again. I had my head on using a standard N-character LCD and perhaps some low-power LEDs for the other indicators, but man! This is just what I've been dreaming of. I'll probably get a couple of screens when they're out.

We could organize ourselves into a pocket computer enthusiasts group after they're all working, what do you guys think? I've been dying to make this little machine communicate to the outside world through the old cassette interface. Perhaps figure out some sort of really basic modem program using the load and save commands, and audio in/out on the other side of the cable.

Greetings from Brazil, where the PC-1211 was built in rather large numbers. Can't wait to fix mine!

rkindig · « **Reply #49 on:** May 26, 2019, 01:50:15 pm »

I'm very curious: how is this project coming? Almost ALL Tandy PC-1's have the LCD issue.

frodonl · « **Reply #50 on:** June 03, 2019, 09:27:27 pm »

While I don't need it yet - my pc-1 only has a VERY small, nearly invisible, bit of leakage in the top-left corner - I sure plan to order one of these displays once they become available. After all, one never knows what might happen in the future.

Great job!

robertbaruch · « **Reply #51 on:** June 04, 2019, 11:42:33 pm »

Yay! The LCDs have come in and are now available for purchase.

This is the end to a very successful project and learning opportunity. I've reached break-even already, and now I'm looking for the next LCD problem child. Suggestions welcome!

--Rob

TERRA Operative · « **Reply #52 on:** June 05, 2019, 03:28:32 am »

Maybe some of the older HP bench multimeters.
They tend to fade and one LCD design could possibly do multiple models.

robertbaruch · « **Reply #53 on:** June 08, 2019, 06:51:20 pm »

I'm actually surprised, I didn't know there were that many PC-1/PC-1211 enthusiasts out there. Of the original stock of 200 LCDs, I've sold half of them already. Possibly I'm in the long tail now, but I honestly thought I'd sell maybe 20 or so.

james_s · « **Reply #54 on:** June 09, 2019, 05:05:56 pm »

I wonder if there is a company that can do custom VFDs in similar low volumes? I know there are various instruments out there with worn out displays. I remember some time back someone did a hand made LED display replacement for a Fluke 45. Actually an LCD version of that might look quite good too.

JCCyC · « **Reply #55 on:** June 14, 2019, 02:39:42 pm »

I'll have two!

demod · « **Reply #56 on:** June 18, 2019, 02:44:24 am »

Thanks, just ordered one!

demod · « **Reply #57 on:** July 21, 2019, 04:44:41 am »

Finaly had a chance to look at my PC-1. Definitely has an LCD problem. Before the new LCD when I power up it I get a display like it is trying to enable all pixels. I don't think this is a LCD problem. Has anyone seen this before? I can't see any obvious issues.

After a reset it changes slightly, and very occasionally it will have a constant beep tone, until reset again. (see attached pics)

Not sure I want to change the LCD when it is like this, might be a waste of time.

(is there somewhere people are discussing repairs to these units?)

aldweb · « **Reply #58 on:** September 29, 2019, 10:00:32 pm »

Hello,

So, I could replace one LCD to one my devices, with success, wonderful. I left a positive review on robertbaruch's Tindie page, he so much deserved it for his work!

When finalizing a second device LCD replacement, still with success (LCD working with full contrast), I had an issue in the final step when you want to remove the wiper on the contrast pot to get the right contrast, because the pot just broke apart (white plastic part to old?)

Reading back this thread, robertbaruch wrote back on April 9th: "A qualified success! Qualified because (a) I still need to reproducibly replace an LCD without several tries, and (b) you have to replace the contrast adjustment with a 240k resistor."

So, would it be enough to unsolder the plot, replace it with a 240 KOhm resistor?
What resistor would you recommend? Would this one ( https://www.conrad.com/p/metal-film-resistor-240-k-axial-lead-0207-06-w-1-1-pcs-421022 ) work for instance?
If you had any picture of the final result, this would help me, thanks.

Thank you for your help,
aldweb

aldweb · « **Reply #59 on:** October 12, 2019, 06:05:11 pm »

Hello,

I will answer myself, in case somebody else would be interested in doing the same thing as me when you find yourself with a defective contrast pot or fail to remove the wiper as explained in robertbaruch's instructions.

So, I replaced the contrast pot with a 240 KOhm resistor.

I removed the contrast pot and cleaned the area from any remaining soldering --> see first picture
I then soldered the standard 240 KOhm resistor --> see second picture

After that, the replacement screen worked like a charm

Cheers,
aldweb

tabajaralabs · « **Reply #60 on:** November 16, 2019, 10:46:37 am »

Any updates on the LCDs? I have a pair of PC1211s waiting for them =)

Keatah · « **Reply #61 on:** June 16, 2020, 05:08:41 pm »

Is it possible to use the yellow-tinted polaraizer with these replacement LCDs?


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Author Topic: LCD design, is this good enough? (Read 25010 times)

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