Another Backlight Question

Ok, i guess ill start off by telling you all what i have and showing the datasheet.

I have an ATMega1280 with a 128x64 TM12864L-2 LCD display. I have it wired as directed using Pinout B:

http://www.arduino.cc/playground/Code/GLCDks0108

I see the animation from the sketch i uploaded, but i have no back light. I've checked the connections on my breadboard and tried 2 different potentiometers. I'm running out of ideas and hope I just missed something stupid.

Thanks in advance.

I have it wired as directed using Pinout B:

In what document? Link missing.

The pot is nothing to do with the back light.

The backlight has a separate power connection to the rest of the chip normally pins 15 & 16. You also normally need a current limiting resistor of a few tens of ohms.

Odd, I included the link to the Arduino Playground… Let me try it again

http://www.arduino.cc/playground/Code/GLCDks0108

Sorry that was me, I saw the link said code in it and just thought it was for the code part not the wiring.

The diagram shows a 220R what did you use? Have you measured the voltage on pin 19 and pin 20?

I used a 220 ohm resistor. And I have not measured voltage on pin 19 or 20.

here's the kicker. When i received the board it came pre wired on the breadboard and the back light worked. I took it off to rearrange things on the breadboard to make room for my RTC and other sensors, and it hasnt worked since.

Well that sounds like you haven't wired it up right, or you blew the LEDs by miss-wiring them. Also if you are using bread board you connections could be loose or strips are joined like you think. Note there is a break in the power strips in the middle. Probe around with an LED and resistor if you haven't got a meter.

thanks for your help, ill poke around with it and see what i find.

Got the backlight working :) I changed the pot and realized the wiring was all wrong (must've had too much happy sauce :blush:)

Thanks for your help!!

ClemQuat: I used a 220 ohm resistor. And I have not measured voltage on pin 19 or 20.

When i received the board it came pre wired on the breadboard and the back light worked.

I have not seen any seller doing this type of service before, kind of nice. Where did you get the display from?