Unknown LCD from old Epson printer (RCD2226 ROHM) - Page 1
Forum section: electronics / beginners

author: edy
author_rank: Super Contributor
timestamp: August 15, 2013, 02:05:20 am
content: Hi folks,I tore down my old Epson inkjet printer and scavenged a few parts, including this control panel that had some buttons with underside LED illumination and an LCD display raised in the middle (I believe it is 2 line).I looked closely and photographed some marks RCD2226 and A7 ROHM but I can't find any datasheet info on it. It looks like there is a driver IC built into the display (under that silver can) so I should just be able to send it commands, perhaps through an Arduino.The pin spacing looks like I could just cut it and slide it onto a breadboard.Any ideas on how to decypher this display would be appreciated. I have no idea what the pins do without the datasheet. I also noticed on the board where the LCD pins are inserting there are a lot of caps and resistors.It would be nice to know how to use it for an Arduino projects. Thanks.

author: WarSim
author_rank: Frequent Contributor
timestamp: August 15, 2013, 02:57:34 am
content: It is most likely one of the standard parallel connections.You can use a multimeter to figure out power pins to help with determining pin order.The best way would be to use a microscope to read the etching on the driver chip, and use the driver chips data sheet for the command set. The printing is tiny and hard to read but in most cases it is there.

author: edy
author_rank: Super Contributor
timestamp: August 15, 2013, 01:19:38 pm
content: Thanks. I guess if it's anything like the Hitachi, then pin1 is +5V and pin2 is ground, with pin3 being a variable pot to control contrast which connects to pin1 and pin2). Connecting a multimeter am I checking for resistance between pins? For example, the data pins should be high impedance because they are not allowing much current flow but just acting to switch transistors? Whereas the power pins should have a lower resistance because they allow current to flow through the display?The LCD I have has 13 pins. Hitachi uses 16. However, I will assume no backlight so we can remove the pin15 and pin16 for backlight voltages. Now assuming we are still using pin4,5,6 the same as on a Hitachi (to the command/character, read/write and E toggle) that would leave only 7 data pins which is 128 bit. I guess it could have a restricted set of characters being a dedicated application, no need for more.

author: Unknown
author_rank: Unknown
timestamp: August 15, 2013, 02:37:42 pm
content: That sounds unlikely. The HD44780 protocol can work in 4 and 8 bit mode, not 7. The large number of fat traces and caps near the connector don't look like HD44780. My guess from the PCB would be that it might be a bare LCD without driver.

author: Codemonkey
author_rank: Regular Contributor
timestamp: August 15, 2013, 02:56:15 pm
content: It looks like it has a chip on glass controller so I doubt its just a bare LCD, but those caps are probably for the charge pumps so at the very least you'll have to copy that bit of the circuit onto your breadboard.

author: WarSim
author_rank: Frequent Contributor
timestamp: August 16, 2013, 02:42:30 am
content: By looking at the pictures closer I an sure it is 4 bit at most. It could also be a multi mode serial driver. The left is a charge pump, decoupling caps or Ve/Vee/Vo smoothing caps. The thick traces are most likely power input. What looks like series resistors could be for level shifting or mode programming. Tracing out the board should help figure this out.

author: WarSim
author_rank: Frequent Contributor
timestamp: August 16, 2013, 02:48:11 am
content: Quote from: alm on August 15, 2013, 02:37:42 pmIf your term of bare, refers to an LCD that has the shift registers and charge pumps that you need to supply streaming data. Yes of course that is the most likely. If you are referring to what i call a bare LCD where you need to manually control a matrix very unlikely.

author: edy
author_rank: Super Contributor
timestamp: August 16, 2013, 03:30:23 am
content: I've attached a photo of the LCD cut from the PCB. You can now see the PCB traces more easily with the associated caps and one resistor (at pin 12). Pin 1 goes through hole to something, maybe ground?Pin 2 is tied to a cap C6.Pin 3 and pin 4 appear to be tied across cap C7.Pin 5 goes to cap5 and passes through holes to other side of PCB.Pin 6 appears to be tied to Pin 9 across cap C10, also a large common plane above.Pin 7 and 8 and 9 have thin traces going up, maybe to flatflex port.Pin 10, 11 and 13 also have thin traces going up and joined to caps C11, C4 and C3 respectively.Pin 12 is going to resistor R14.

author: redben
author_rank: Contributor
timestamp: August 16, 2013, 09:37:33 pm
content: If I were you I would take a look at this :http://justpushbuttons.com/blog/?p=263The topic is quite similar