Interfacing a unknown LCD - Page 1
Forum section: electronics / beginners

author: Neptune
author_rank: Newbie
timestamp: April 15, 2023, 12:16:33 pm
content: Recently, to learn, I wanted to recover the projector from a alarm clock to interface it with an arduino. However I can not determine the protocol used nor the controller of the LCD. I have the following outgoing pins marked on the PCB:WR, DA, CS.I already tried to analyze the signal with a logic analyzer but no clues, i'm a newbie.It looks like a serial communication but I don’t know any more.Do you have any ideas?Thanks.(sorry for the blurry image, tell me if you need a better picture)

author: tooki
author_rank: Super Contributor
timestamp: April 15, 2023, 01:00:58 pm
content: That’s probably SPI. DA=data (i.e. MOSI), CS=chip select, WR=write mode.

author: redkitedesign
author_rank: Regular Contributor
timestamp: April 15, 2023, 01:26:48 pm
content: You've got 5 wires going into the board. Start with finding out which ones are power and ground.There is also an LED for illumination. Find out (follow the traces) if it is always on, controlled by an IC on the board or by one of the 5 wires.All unidentified wires: Trace them and see if they go into the IC under the black blob.Protocol to control that IC can be I2C, RS232, SPI, or something propriatary.If you can probe the wires while its operational, check them all.If it toggles regularly, but low-frequent: Its a chip select.if it has regular, but short spikes: Its either an acknowledge or an frame-syncif if toggles fast but regular (fixed frequency, 50% duty cycle): its a clockif it toggles irregular, its data."Regular", "infrequent" and "short" are all relative to the other signals.Lookup patterns of I2C (clock+data), SPI(clock+data+chip select), RS232 (only data) on the internet and you'll see that you can easily identify them.Once you know the protocol, deduce the data being sent. Correlate that to the image produced and you'r done!

author: Neptune
author_rank: Newbie
timestamp: April 15, 2023, 01:39:53 pm
content: thank you for your answers, I have already identified power and ground. The LED is controlled by the IC (I think). Thank you for your advice I will trace every track of the PCB since this PCB is not very complex.

author: DavidAlfa
author_rank: Super Contributor
timestamp: April 15, 2023, 01:48:16 pm
content: Sorry for the blurry image?Was the effort of making decent pictures so hard? Half of the board missing...

author: Neptune
author_rank: Newbie
timestamp: April 15, 2023, 02:11:07 pm
content: Didnt see it was cut sorry, I added a better onebtw this clock was VERY cheap and PCBs are not good

author: DavidAlfa
author_rank: Super Contributor
timestamp: April 15, 2023, 02:43:01 pm
content: But make at least make a picture where part numbers and traces can be seen.Do you have the usual 24MHz cheap analyzer?

author: Neptune
author_rank: Newbie
timestamp: April 15, 2023, 02:58:44 pm
content: Nop, i dont have a "real" 24MHz analyzer, i got one coming soon. For now im only using an Arduino.For the picture the PCB is really small, im trying my best.

author: DavidAlfa
author_rank: Super Contributor
timestamp: April 15, 2023, 03:29:03 pm
content: Now we're talking, decent pictures there!