Reverse engineer a dot matrix display  - Page 1
Forum section: electronics / projects

author: THORs_Hand
author_rank: Contributor
timestamp: August 19, 2017, 06:48:05 pm
content: Hello everyone, I have this dot matrix display from an Sagem F920 POS (as we call it in our country, it's the stuff that you pay with your card I don't know how it's called elsewhere) and after a long time I decided to open it up to analyse it and I discovered that I could really use this LCD with my arduino/Raspberry pi but I simply don't know anything about how it communicates or which pin is which, there's no part number no nothing.. Can someone help me find out how to control it?Sent from my SM-J510FN using Tapatalk

author: danadak
author_rank: Super Contributor
timestamp: August 19, 2017, 10:45:25 pm
content: Any markings/stickers with part numbers on backside of LCD ?If not contact Sagem and ask them for the vendor / part numberof the display.Then possibly you can get a datasheet, or at least pinout and pin namesthat would help.Regards, Dana.

author: SL4P
author_rank: Super Contributor
timestamp: August 19, 2017, 11:02:24 pm
content: Without knowing your budget, you could also go on eBay or other site - and buy a new documented display in box for less than the $time spent looking for the one-off paperwork (talking $10-20 here). It's an interesting hobby hunt, but risky if you ever want to make more than one gadget.Does it have driver ICs on the back of the panel?AC or DC driven?Sagem and Type number will be your friends.

author: Ian.M
author_rank: Super Contributor
timestamp: August 19, 2017, 11:10:23 pm
content: If no data is available, is the POS capable of being powered on and displaying anything on the screen? If so, measure voltages, scope for signals and when you find them hook up a logic analyser and see if you can decode the protocol and commands. Its a *LOT* of work and a POS card reader is likely to have additional security features to make it more difficult to reverse engineer so probably isn't a good beginner's reverse engineering project.

author: jmelson
author_rank: Super Contributor
timestamp: August 20, 2017, 02:34:38 am
content: If you can set up your Arduino / Pi to generate two square waves at a few KHz, and complementary (one goes high while the other goes low) then you can excite various terminals on the display, and dope out what pin connects to which pixel. If it is truly a dot matrix, then one set of pins should drive each horizontal row, and some other pins should drive each column.Jon

author: Ian.M
author_rank: Super Contributor
timestamp: August 20, 2017, 02:52:52 am
content: No you cant. That black area is most likely to be a COG (chip on glass) so its some sort of smart display*. Because larger capacitors and inductors cant be fabricated on an IC or mounted on the display glass, they usually need quite a few extra components to provide all the different voltage rails the LCD driver COG needs, so getting it to display anything without data or an operating main board is virtually impossible. All injecting square waves will do is blow the COG, and turn it into scrap.However that technique is valid for 'dumb' bare glass segmented displays.* it just doesn't have enough pins to be a bare glass matrix LCD and we know it cant be a simple multiplexed segmenteted display because of what its out of

author: THORs_Hand
author_rank: Contributor
timestamp: August 21, 2017, 05:28:42 am
content: After a bit of work found out the following :No part number anywhereIt is a multiplexed display, pin 1 and 2 power the back light and the rest unknownCould be a serial or 4 bit parallel connection between the board and the CoG because of the way the board was wired putting pins 1 and 2 on power rails and the rest to an AtMega secure microcontrollerWorks on DC 3.3V only that could be just a standard 128x64 dot matrix display. I got it out of an working pos and destroyed it by opening it. Could that be of any help?Sent from my SM-J510FN using Tapatalk