LCD Problems

Testing/Troubleshooting
1

Hey All,

I seem to be having problems with some 40x2 lcd modules I have purchased. One is based on the KS0066 controller and has model number TM402C from Tianma. The other is the Wintek WM-C4002M-1yly but I don’t know its controller. The data sheet for the Tianma model is here http://docs.bgmicro.com/pdf/lcd1025.pdf and a sheet describing a similar lcd from wintek is here http://www.wintek.com.tw/ModuleList.asp?LcmType=&DispType=CHARACTER&ModuleNo=WM-C1602M-1GLYf

I also have a 16x2 lcd that works when connected, however when I connect the 40x2 displays nothing will show up. Could this be due to the displays requiring a negative 0.3V on V0, as described in the tianma module. Or do these displays need negative contrast voltage?

2

Hi,

do you see a gray/black line when the LCD is powered and not initialized?

This would indicate, that the contrast voltage is ok. If not, this Wiki page helps: http://www.midibox.org/dokuwiki/doku.php?id=troubleshooting_lcd_displays

Best Regards, Thorsten.

3

I see the black line when I connect my 16x2 ( which I thought stopped working but then realized I broke the Enable line), however when I connect either 40x2 I see nothing. I was able to find this datasheet on the Wintek LCD http://www.cyfronika.com.pl/dokumentacje/wmc4002.pdf  however I see nothing about needing a negative contrast voltage. The data sheets say VDD-V0 for both should be 4.5V. With VDD at 5V that would mean V0~0.5V . I just don’t want to destroy the module with a negative contrast voltage ( or anything else for that matter).

4

I more read the datasheet as VDD is typical 5V and VO as well.

Looks to me like you have a positive constrast LCD…

Best regards,

Lall

5

Thanks for reading the datasheet Lall, however I can’t see any reason why the 40x2 displays won’t work they can’t both be dead (or can they?). And yes my core is working fine, I can get the 16x2 to work fine. I will try testing everything out when I get the chance perhaps I swapped some cabling somewhere. If anyone else has any ideas, let me know. By the way, would placing a negative contrast voltage on the LCD damage the controller at all, were these controllers designed to handle it?

Sincerely,

JJC