Identify LCD pins - Page 1
Forum section: electronics / projects

author: acsehi
author_rank: Newbie
timestamp: December 07, 2020, 07:38:35 pm
content: Hi, I am new here, and however always courted with electronics, so please be gentle, I do not have much experience with it (except basic stuff like, building with Arduino, so it is like Lego).In the last couple of months I cooked (literally) two Ikea kitchen timers, so I thought, maybe I could build a small circuitboard with STM32 and recreate the timer itself. I know it is more feasible to buy a new one, and I know all the reasons, I should not do it, but...So my first question is:I have the LCD from the timer, it is 4 7-segment and a colon, like this: 88:88It has 12 connections to the board. Is there a (not too complex) way to tell, which one which?Thank you all the answers.

author: ataradov
author_rank: Super Contributor
timestamp: December 07, 2020, 09:21:10 pm
content: In many cases there are visible traces going to the segments. You may need to play with the light and get the angle just right.But the LCD would be just glass, so you would need an MCU with the LCD driver. They are not just regular digital signals.

author: amyk
author_rank: Super Contributor
timestamp: December 08, 2020, 01:23:41 am
content: 12 pins and that layout suggests it could be something like this:https://www.lumex.com/spec/LCD-S401M16KR.pdfA few volts battery and some wires will let you figure out the connections. Don't apply voltage for too long or you may risk electrolytic damage. You can drive them from an MCU GPIO if the voltage is high enough to produce sufficient contrast.

author: Miti
author_rank: Super Contributor
timestamp: December 08, 2020, 03:13:28 am
content: I made a couple of boards with segment LCDs and PIC16F946. You’ll need about 3 - 5V AC to find the lcd configuration, either from a small transformer or from a waveform generator ( recommended). Don’t use DC, you’ll damage it. Try first touching between one extremity and a middle contact, see what segments come on and maybe you can figure out the commons. The rest is easy. Read the PIC16F946 (and family) data sheet to see how LCDs are driven. That’s just for your info because once you know your lcd configuration, setting PICs registers is a piece of cake. Also, AN658 from Microchip is a recommended read.Cheers,Miti

author: acsehi
author_rank: Newbie
timestamp: December 08, 2020, 03:57:40 pm
content: Thank you for the answers, i will check the pins as you suggested. BTW I wanted to use the following driver for it: HT1621 (https://datasheet.lcsc.com/szlcsc/Holtek-Semicon-HT1621B_C7532.pdf) it seems OK, and it seems cheap enough, with a low power STM32 as a brain, it could fit to the boardspace that is available.Again, thank you all the advice, and the datasheet, it seems I am not that good using google

author: Miti
author_rank: Super Contributor
timestamp: December 08, 2020, 08:33:18 pm
content: STM32 and dedicated LCD driver for a timer with 30 segments is waaaay overkill.

author: Miti
author_rank: Super Contributor
timestamp: December 17, 2020, 02:40:49 am
content: I found a diagram for one of my LCDs that looks pretty similar to yours. Left to right or top to bottom, hand writing is COM # and SEG #. For example 3 6 is COM3 SEG6.I've also posted pictures of another project that measures in sequence atmospheric pressure, ambient temperature and battery voltage. It was my first segment LCD project, just for learning and to see how low power I can push it. That label shows the last battery charging date. Both unfinished projects BTW, that's my signature...

author: cdev
author_rank: Super Contributor
timestamp: December 17, 2020, 03:06:14 am
content: I have old LCD displays which I don't know the connections for but here is an interesting phenomenon, they are so sensitive that by simply touching pins with your fingers you can see them change opacity. You could probably use the tiny amount of static or the tiniest amount of DC that causes them to get black to determine what pins are active with what segments.

author: Miti
author_rank: Super Contributor
timestamp: December 17, 2020, 02:52:37 pm
content: @ cdevFrom my experience, you can see one or two segments by touching the zebra connector or the pins, but you can’t reliably find which segment pin goes with which common. You need AC , preferably square wave with adjustable amplitude to do that.

author: cdev
author_rank: Super Contributor
timestamp: December 17, 2020, 03:10:50 pm
content: That definitely sounds like the way to go.Quote from: Miti on December 17, 2020, 02:52:37 pm

author: NivagSwerdna
author_rank: Super Contributor
timestamp: December 17, 2020, 03:20:46 pm
content: First some homework for you...http://ww1.microchip.com/downloads/en/AppNotes/00000658B.pdfThen tickle it with a few volts AC... AC is required so as not to damage the LCD but for short periods of time you might get away with a bit of DC or create fake AC using two digital pins and alternate 0s and 1s...Using a driver is a good idea or use a uP with inbuilt driver (e.g. PIC24FJ128GC006)Have fun

author: algorithm
author_rank: Regular Contributor
timestamp: December 17, 2020, 03:53:00 pm
content: Quote from: ataradov on December 07, 2020, 09:21:10 pmWould this be the way to do this with a color lcd? I recently got something with a broken LCD. I pulled out an LCD from a broken 2mp camera I had around with the intention of trying to rig as a replacement. Wasnt quite sure how to figure the connections out without trial and error and better judgement. But can I just power the device with the broken LCD removed and see what connections work on the working lcd?

author: cdev
author_rank: Super Contributor
timestamp: December 17, 2020, 04:05:22 pm
content: Thank you for telling me that. I was under the mistaken impression that DC was what I should use for an application I want to construct. Luckily I hadn't gone poking around and made the mistake I probably would have, yet.I am kind of interested in stereography, and getting a system set up to view 3D with LCD shutter glasses someday. (although my current monitor will only do 70 Hz, so its probably going to have to wait until I can either afford a 120 Hz one or figure out how to use my current monitor).I have an ancient pair of SimulEyes LCD shutter glasses that were made to work with VGA, and DOS games. But I think they could be made to work, if I can figure out how to interface them to a modern driver and provide them with the signal they need to toggle back and forth.So need to do my research. I should really go to the tech support blogs at Nvidia and/or AMD, the card vendors/driver makers. I'm pretty sure these glasses are like all other shutter glasses and can be substituted for DIY - basically any other similar ones.LCD stuff of many kinds are very cool. Once, more than two decades ago I want to a party at a loft in SF (the people holding the party rented it for the event) and they had a bathroom enclosed in LCD glass, which was transparent but would become translucent (like ground glass so privacy was maintained) when somebody was in the bathroom.Surprisingly, its still very expensive stuff.It would be neat, especially if it was affordable, to be able to make custom displays to order. But I deeply doubt if it would be, and think I remember a discussion here about it being pretty expensive. I suspect, though, low current requirements of LCDs make them a really useful choice- battery life being the important thing it is.Seems that LCDs have very long life, also, potentially. I suppose one can make custom displays with any graphics LCD now so if the power is available to drive a display with a bit more power, economics of a custom LCD might only make sense if you have an old device with a broken or frequently failing device you need to resurrect in quantity. (And then the way to approach it might be emulation with a generic display, rather than making a custom one?) But certainly the standardized ones are hard to beat for cost.

author: ataradov
author_rank: Super Contributor
timestamp: December 17, 2020, 05:10:25 pm
content: Quote from: algorithm on December 17, 2020, 03:53:00 pmNot by visual inspection. Color LCDs have a controller on the glass. Looking at the traces will not help at all.Quote from: algorithm on December 17, 2020, 03:53:00 pmIn theory - yes. In practice - you need to know what you are looking for. You need to know what general types of interfaces exist and your goal is to identify which one is used in the LCD. Blindly pocking at the signals with the scope will not help.