LCD Negative Voltage, Contrast Flicker - Page 1
Forum section: electronics / beginners

author: Engelon
author_rank: Newbie
timestamp: February 02, 2019, 02:14:05 pm
content: Attempting to get a LCD working identical to the one mentioned herehttps://forum.arduino.cc/index.php?topic=196589.0i have supplied it with a negative voltage from 2xAA batteries as mentioned in the post. Except I seem to be getting a weird flicker, and have no clue what could be causing it. I recorded it to save me trying to describe whats happening:https://youtu.be/S0k4qeS0_UMthe scrolling rows are not due to the camera and everything is as it appears in the video.It's currently connected to an arduino uno running the paged GrapicsTest sketch from the u8g2 library using the constructor U8G2_T6963_256X64_1_8080, not that it matters as I don't think the issue is due to the arduino.Any thoughts as to the cause of this would be helpful i'm happy to try almost anything as this LCD was saved from the bin.

author: Buriedcode
author_rank: Super Contributor
timestamp: February 02, 2019, 03:25:17 pm
content: It could well be the LCD is damaged in some way. Or that you're not supplying enough negative voltage - two AA batteries can at best provide -3.1V. 240x64 displays generally require -7 to -11V (referenced to GND, but the datasheets reference this to VDD making it ~-13V).With that said, to a high contrast voltage would probably mean it displays nothing rather than flickering, it is difficult to say if the display is functioning correctly without the correct conditions:-Stable 5V supply.-Adjustable contrast voltage from -7 to -11V capable of about 5mA.-A verified pinout of the display-A verified initialization sequence for the T6963C.I have used the u8g2 library myself, and whilst its very inefficient - it did work nicely with the T6963C displays I have so it probably isn't the library.This page has the pinout:https://www.hobbielektronika.hu/forum/karakteres-lcd-k-meghajtasa-vezerlese?pg=6and suggests using two 9V PP3 batteries for the negative voltage. You could also use a ICL7660 or equivalent to generate the bias voltage, but for testing its just easier to use two 9V batteries. Even one would probably work well enough for you to test the display (thats -9V).

author: Engelon
author_rank: Newbie
timestamp: February 03, 2019, 11:32:40 am
content: I tried each of the things you suggested and am fairly confident the issues are due to poor connections.I tried a higher contrast voltage but everything too far below or above -2.3v gives me a blank screen.The next thing I tried was to double check the pinout of the display and everything seemed to checkout.I wasn't sure about the initialisation sequence, but i notice tilting the display seemed to make the issue better and worse, so i tried to reduce the number of jumps between the display and arduino, instead of going LCD -> jumper -> breadboard -> jumper -> arduino, I shortened it to LCD -> jumper -> arduino and ended up with a major improvement

author: Engelon
author_rank: Newbie
timestamp: February 05, 2019, 12:45:42 pm
content: For future reference, anyone with MG 817AU-LA-07 the contrast pin 4 needs 2.5v.Pinout:DESCRIPTION:GND|Contrast|RD|C/D|Reset|D1|D3|D5|D7|NC|NC|Backlight GroundPIN:2|4|6|8|10|12|14|16|18|20|22|24------------------------DESCRIPTION:GND|VDD|WR|CE|NC|D0|D2|D4|D6|FS|NC|Backlight +12vPIN:1|3|5|7|9|11|13|15|17|19|21|23