I just got my 128 x 64 GLCD from adafruit. I wired it up according to the pin out B on the library post Its powered up but I don't see it draw anything. It just shows the white dots on the whole GLCD. Anys suggestions are welcome. Thanks

Perhaps its just the way the photo was taken, but it doesn't look like all the pins are wired.

There is 20 pins but all are not used. I have it wired according to library page posted above. I have checked it like five times. The only thing that doesn't make sense is the pot has one wire to ground, one to the wiper, and one that just connects back to the LCD. Shouldn't one pin be power one the wiper and one to ground? Since my l d is blue and white should. Code say draw in white?


The only pins that you can leave unconnected are the backlight pins. It looks like you have not connected up all the data pins?

MEM was right. All pins need to be hooked up, Duh! Anyway, I now have the lcd up and running but its like the contrast is set to the max and I can get it turned down low enough. The 10k pot that came with the GLCD barely does anything when move to both extremes of the pot. I went an got a 100k pot (they didn't have anything closer to 20k) and put it in and it doesn't change contrast anymore than the 10k pot did. I also bought another 10k pot just to make sure that the one I had was but, but new 10k pot acts just like the one I replaced. I can only see the sketches if viewed from an angle. Attached are pics showing the GLCD.

I've tried changing the initalize GLCD setting from INVERTED to NON_INVERTED but GLCD still has way to much contrast and sketch can only be seen from an angle.

Not sure what else to I am about to give up on this GLCD.

LCD Viewed From Angle

LCD viewed straight on

a 10k pot should be fine. One side of the pot goes to ground (glcd pin 1), the other side goes to glcd pin 18. The center pin of the pot goes to glcd pin 3.

I double checked and that's the way I have it hooked up. I measured the voltage to the contrast in pin on the LCD (Pin3) and its 5V(The pot is turned all the way to one end). The library reference page for the GLCD says it should be 3 - 4 V. Could I just have a Bad GLCD?

What's the voltage when the pot is turned all the way the other way?

14.25 V

The library reference page for the GLCD says it should be 3 - 4 V.

it says:

Check contrast voltage (typically between -3 and -4 volts) on contrast-in pin of LCD panel.

thats a negative voltage. is the voltage on pin 18 negative with respect to ground?

When I mesured GLCD pin 3 before was reference to +5V. I remeasured GLCD pin 3 with voltage referenced to ground and got the following voltages.

GLCD Pin 3 Voltage with Pot extreme end 1: 0 GLCD Pin 3 Voltage with Pot extreme end 2: -9.15V

GLCD Pin 18 Voltage with Pot extreme end 1: - 9.04 GLCD Pin 18 Voltage with Pot extreme end 2: - 9.14

The pot does not seem to be connected to ground, with the power off, can you measure the resistance of both ends of the pot to ground

For some reason I can't get my multimeter to even read a resistor so not sure what that means for my voltage measurements. I will have to borrow or get another multimeter and remeasure.

Just so i understand what you want. leave pot in my breadboard with the power off. One multimeter lead goes to ground the other lead goes to one end of the pot. Move the one lead to the other end of the pot and remeasure.

thats it. One end should read around 10k ohms (its not critical), the other end should read a couple of ohms at the most. If you dont get a reading of under 10 ohms on the side connected to ground, your ground connection isn't working.

Ok, So I finally got a multimeter that works. Here is potentiometer readings

Pot by itself 5.2k ohm Pot on board and referenced to ground Power off End 1: 0.5 ohm End 2: 3.9k ohm

I assumed this pot is bad since its supposed to be a 10k pot. So I put in a new 10k pot and remeasured.

Pot by itself 9.3K ohm Pot on board and referenced to ground power off End 1: 0.5 ohm End 2: 5.82k ohm

Voltages referenced to ground Pin 3 Pot at 1 end: -9.41V Pin 18 Pot at 1 end: -9.41V

Pin 3 Pot at 2 end: -3.3V Pin 18 Pot at 2 end: -9.31V

After all that it seems that my ground is working but even with the new pot the contrast is still bad. Let me know if there is something else or should i assume something is off in the GLCD.

Pot by itself 9.3K ohm, Pot on board and referenced to ground power off: End 1: 0.5 ohm,End 2: 5.82k ohm

If you measure the resistance at the slider, does it range between those two readings? Do you get the same resistance reading if you measure at pin 3.

I suspect either your pot is faulty (the slider is not making correct contact) or the pot is not wired correctly.

All measurements referenced to ground Slider at pot 5.75kohm at pin 3 5.75kohm

I took all wires off expect ground, power and pot wires. Its wired correctly but still still contrast is to high. I have put 3 new pots on this board and GLCD does the same thing.

I finally dug out another LCD that I have a 20 x 4 lcd that I put on breadboard and the same pot that doesn't work on GLCD controls contrast to that 20 x 4 lcd so I am marking up this up to bad GLCD.

Thanks for all your help it is greatly appreciated.

if one end of the pot measures 5.75 k and the other end measures around 1 ohm, then if you measure the resistance on the slider you should read 5.75k when it is at one end and around 1 ohm at the other. In other words, when the slider is touching the end that measures 1 ohm (or so) the resistance to ground measured at the slider should be close to 1 ohm. if not, then there is something wrong with the pot, wiring or measuring method.