How to interface with this unknown LCD? - Page 1
Forum section: electronics / beginners

author: Cherenkov11
author_rank: Contributor
timestamp: July 23, 2018, 11:06:54 pm
content: I removed a LCD from a board that I had, mainly because I wanted it for an arduino project, but, I faced that there is no type of number part of any kind. So, I removed the plastic of the 8-pìn connector and found a silk-screen of the name of the pins, but I do not know what they mean.The only 2 pins I identified are: K and A, for the blue backlight.I remeber that it is a custom LCD, that showed Input voltage, output and bars of the percentage.So any idea of how can I interface with this LCD?Images:

author: Nusa
author_rank: Super Contributor
timestamp: July 23, 2018, 11:15:44 pm
content: A mystery LCD from a mystery board that has a backlight and an 8-pin connector. You found labels for the pins, but didn't tell us what the six unidentified ones said. Not enough clues, sorry.Pictures would probably help the most. Both of the LCD and the board it came off of.

author: Cherenkov11
author_rank: Contributor
timestamp: July 23, 2018, 11:17:08 pm
content: Sorry, I forgot to put link of the image, now it is

author: reboots
author_rank: Regular Contributor
timestamp: July 24, 2018, 12:26:26 am
content: Wild guess:/CS - Chip Select (active low)/RD - Read (active low)/WR - Write (active low)DI - Data Input?VSS - Negative supply (ground)VDD - Positive supplyThis looks like a primitive serial data interface. I would trace the connections on the host board, and find how those signals are connected. If you can power up the host board and have some means of monitoring the signals to the display, even better.You could try applying 3-5V across VDD and VSS, tying /CS and /WR to VSS, and pulsing DI to see if anything shows up on the display. If that produces results, you'll still have a challenging task in reverse-engineering the protocol.

author: Nusa
author_rank: Super Contributor
timestamp: July 24, 2018, 01:29:31 am
content: Here's my guess for the controller IC under the epoxy:http://www.seeedstudio.com/document/HT1621.pdfApparently there are a number of HT1621 libraries out there...I did the search and saw a number of hits, but didn't look at them.

author: amyk
author_rank: Super Contributor
timestamp: July 24, 2018, 02:31:48 am
content: Quote from: Nusa on July 24, 2018, 01:29:31 amProbably not, because OP mentioned it's a "custom" LCD with shaped segments (i.e. not a bitmap display). The interface suggests a very simple controller, probably not much more than a shift register.

author: Cherenkov11
author_rank: Contributor
timestamp: July 24, 2018, 02:56:50 am
content: Perhaps the option that Nusa says may work. Yes, it is a custom LCD, I think it came from a solar charge controller, thus, it have a bunch "7 segments number" on it, and some little symbols and bars. So, I'm going to try some libraries for the HT1621 and see what happen.BTW, the only purpose of this is just to learn and not to give it a practical use.

author: tsman
author_rank: Frequent Contributor
timestamp: July 24, 2018, 02:59:28 am
content: Quote from: amyk on July 24, 2018, 02:31:48 amHT1621 isn't a matrix LCD controller. It is intended for those custom shape segment LCDs.

author: Cherenkov11
author_rank: Contributor
timestamp: July 24, 2018, 03:31:14 am
content: Good news, Nusa was right, it is a HT1621, I downloaded a library for arduino and compile the example that came with the library and a group of segments lit up.Thank you to you all, I'm going to continue experimenting with the library, since now I have a solid base.

author: Cherenkov11
author_rank: Contributor
timestamp: July 24, 2018, 03:55:35 am
content: With another library that comes with a LCD tester that basically fill the RAM of the HT1621 and all patterns lit up, and little by little, emptying the spaces of memory, therefore, the patrons go off one by one and then all the LCD turns off. So, it is a success, Thanks all again.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 24, 2018, 09:24:22 pm
content: Congratulations on your success. A double win since the upper half of that custom LED has some pretty general purpose use. You could do all sorts of interesting little projects with that. The lower right quadrant also has possibilities.

author: vejitha
author_rank: Newbie
timestamp: December 25, 2020, 10:51:58 am
content: Hey. Are you able to control all the segments individualy

author: ebclr
author_rank: Super Contributor
timestamp: December 25, 2020, 07:12:46 pm
content: For sure HT1621 is very simple to usehttps://www.holtek.com/productdetail/-/vg/ht1621