# 320x240 dot matrix LCD power connection

I'm interested in buying some LCD for my amateur Z80 retrocomputer, and I'm searching for 320x240 dot matrix screen with 8-bit parallel bus.

What is common for them all, they need 3 independent power connections: for logic, LCD itself and backlight... and for LCD the voltage is quite high - 23V (why is it so high?). I would like to ensure how to properly connect it without burning.

Pls see this example and that table:
https://www.aliexpress.com/item/1320170071.html

As I understand:

• connection for logic is between VSS and VDD: 5V
• connection for backlight is between BLK and BLA: 5V
• connection for LCD: it needs 23V, but I'm not sure where exactly. There's written VDD-VO=23V. Does it mean I have to connect independent supply of 23V, where (-) to VO and (+) to VDD? There is also another pin: VEE, which is "output voltage for LCD" - this one is totally confusing.

Or maybe using such LCDs is dead end for amateur project?

• Get components with datasheets that tell you how to connect them. End of story, really. No helpful datasheet, no sale. – Marcus Müller Mar 26 at 20:29
• Serach not only for pdf to screen, but also controller inside – fifi_22 Mar 26 at 20:32
• @RaspbJan, If you look closely there you will see a potentiometer in the vacinity of VO. It also appears that their power module puts out VEE for you to use with the potentiometer. It's very common that LCDs used a weak negative voltage as contrast control and that you will want to make adjustments with the potentiometer for that purpose. Looks pretty normal to me, except that they are conveniently giving you a negative rail so all you need to add is the potentiometer. – jonk Mar 26 at 20:52

These displays use a negative supply of something like -25V for the LCD. There is a pot from that supply to Vss (10K or 20K) to adjust the contrast. Typically Vdd-Vo is 23V at 25°C so the voltage at the pot wiper would be about -18V. The pot is used to adjust the contrast to compensate for variations from glass to glass variations and with temperature and voltages and viewing angle.

As @jonk says, this one appears to have a DC-DC converter to generate the negative voltage, so you should only need to supply +5 and the backlight current, which is quite nice compared to some competitive panels.

See below. The green arrow and circle show you the controller which you must also track down in order to work out the details of communicating with the LCD display. (See link to controller below picture here.) The red arrow points to where you can spot the potentiometer being used for contrast control. Take note that it appears that $$\V_\text{EE}\$$ is an output of their power module, so it's providing a convenient negative voltage source for your use with the potentiometer. Another red ellipse circles $$\V_\text{EE}\$$ on the pinout.

Most of the information you need to use them is in the datasheet for the controller.

You can also find libraries that support the controller (which is a Taiwan clone of the Epson SED1335), so you don't have to write all that code yourself.

I don't think it would be a huge deal to get this going, subject to the usual risk in dealing with Aliexpress sellers.

• May I add (insert into your answer) a snapshot of the data from that website with circles around the controller ID and the VEE and potentiometer areas? (You can examine it here.) – jonk Mar 26 at 21:04
• Well, now you get to review what I did and adjust as necessary! – jonk Mar 26 at 21:13
• Ok, thank you guys a lot, seems to be clear :) if VEE provides appropiate voltage to use with potentiometer - it's a nice thing, I'll check it with voltmeter first. Concerning the RA8835 controller I reviewed it before, and it looks to be quite easy to use. Thks. – RaspbJan Mar 26 at 22:30
• @RaspbJan I think you'll be fine with this. It's spendy (to my mind, as I've paid a lot less than this for 320x240 displays.) But it includes a nicer power module, too. I had to add a weak negative rail of my own. So all in all, I think you'll be quite happy. – jonk Mar 26 at 23:31
• @jonk really do u think it's spendy? I was looking for similar things on aliexpress and it's rather normal price. If you can advise some cheaper models - I would appreciate. But if they need much more circuitry to run - i won't bother. I'm trying to connect something more interesting than 2x16 LCD to my homebrew 8-bit computer. My long aim is to build simple VGA graphics card... but definitely not at this moment :) – RaspbJan Mar 27 at 0:05