Can anyone guess which chipset this LCD may be based on? - Page 1
Forum section: electronics / projects

author: nali
author_rank: Frequent Contributor
timestamp: November 28, 2017, 01:23:10 pm
content: .. if anyI want to re-purpose a digital room thermostat with my own firmware. It basically comprises of a PIC, EEPROM and RTC - all pretty straightforward.The LCD is a bit of a problem though. It's a custom job with a discrete segment display mounted on a PCB, with a COB blob being the only active component. The nCS RnW DATA signal lines are helpfully labelled though which should help.So the question is, might this be compatible with a "standard" device? I've used matrix type LCD displays a few times which are invariably based on a HD44780, but never anything with discrete segments so I don't know what's what in that area.Thanks,

author: phil from seattle
author_rank: Super Contributor
timestamp: November 28, 2017, 11:19:40 pm
content: Pretty hard to say with so little to go on. Which pins go to the LCD? You could try to sniff out the protocol. A logic analyzer would be good but you could put together a microcontroller based sniffer to capture the data. I'd use an arduino. It should be pretty easy to send the data to a pc. Once you figure out the clock line, you can probably figure out what it's doing.In the future, it would be helpful to provide things like the make and model of the device, a picture of it (not just the back of a PCB) and any other info you have.

author: nali
author_rank: Frequent Contributor
timestamp: December 01, 2017, 02:17:06 pm
content: OK thanks. I know that "what is this" type of posts with little or no information can be a bit frustrating, but in this case there really is little or no information! The PCB is the LCD module itself, the other side is just wall-to-wall LCD which is a custom LCD made of individual segments as opposed to a bitmap.I'd be deluding myself if I was expecting someone to pop up & say "that's a xxxxxx", although I was hoping that there were some common or classic LCD controllers on which this one might be based to help with sniffing or some trial & error. E.g. like a lot of character type displays are based on the venerable Hitachi 44780.There literally are just the 3 signals to the module: CS, WR and DI so it's some form of serial interface not SPI or I2C. The unmarked pads are not connected to the host, and all the connections on the edge of the PCB are just connections to the actual LCD segments. Not sure if the WR line is a read/write or another enable pin.I've attached a couple of images of the LCD front & it working - but they don't really help with the module

author: coppice
author_rank: Super Contributor
timestamp: December 01, 2017, 02:32:40 pm
content: Most small LCD displays with a blob covered controller chip are roughly compatible with the Hitachi 44780. The snag is many are not 100% compatible, and the character order of the actual LCD panel is not always the same. So, displays don't always work as simple drop in replacements. If you have a display around which are of a suitable size its always worth trying it. There is a reasonably good chance it will work.

author: nali
author_rank: Frequent Contributor
timestamp: December 01, 2017, 05:55:05 pm
content: I had a day off today so managed to spend a bit of time looking at this. After looking at the data I think it may be based on a Holtek controller e.g. HT162x. If so the WR line clocks the data in on a rising edge, and on this basis the packets start with "101" which tallies with the Holtek datasheet.The actual timing looks a bit weird because the WR is all over the place not a nice squarewave like the datasheet. But I guess that's because the PIC will be servicing interrupts for stuff like scanning switches ADC conversions etc, and it shouldn't matter if the data is clocked.Annoyingly I've just found out I've left my ICD3 at work so won't be able to have a play until next weekendTiming diagram below if anyone's interested.