LCD stopped working

Hello and thanks for such a fun product.
I have sadly run into a small problem I am still trying to figure out.
I didn’t find anything similar in the forum so let me go through the details I have.

  1. unpacking, default demo working fine
  2. Installing avr studio, compiling demos from libpololu-avr-100607, programming, everything works perfect

Here between two programming I noticed a “glitch” on the LCD, after programming for a sec all char were black. The demo before the programming was the basic line follower. The demo I programmed, I don’t remember, but it worked, but I don’t remember if it even used the lcd.

  1. Next day, starting the device, no sign of life from the lcd anymore. Everything is still working fine.

So I just though I toasted my lcd while programming the 3pi, so I go try another lcd with similar pin conf … 854796.pdf

But no luck also, so I’m wondering what is the next thing to check. I am really suspecting that I might have just done something silly and not realizing it.
Checked with my voltmeter that data lines are still connected between the LCD and the atmega.

The voltage between gnd and pin of the LCD are (line follower pid start screen):

  1. 0v
  2. 5v

ok when I measured pin3 shorting pin 1 and 3 for a short moment the text appeared on the LCD.

I hope this is enough clue to help me.

So PIN 3 is the LCD contrast. Grounding it, makes the lcd darker (pin 3 voltage is 4.19), the behaviour is such that when I ground pin 3, it will show the text normally and then darken step by step to full dark within 1 sec.
The behaviour is the same with both LCD


Have you tried adjusting the contrast potentiometer on your 3pi?


Well, that was a good guess, I’ll try it tomorrow when I get back to work! Thanks! I tried to play with the pot but not knowing for sure, I quit too quickly.

Edit: yeah, it was that. thanks very much.