# Am I overdriving the pixels of my 12864ZW LCD if I have no resistor connected?

I have the backlight hooked up to 5V and I use a resistor only if I want to decrease the brightness, and no resistor has been working fine. Then I have the one that lights up the pixels hooked to 5V with no resistor, and it worked fine for a while but now if I have it active for more than a few minutes the pixels start to fade, like an overdriven LED, and they go back to full brightness after the Arduino is turned off for a while.

Do I need a resistor connected to it? If so, how small can I get and still make it have an effect? Because a 330 ohm is drastically decreasing the brightness of the pixels and I'd rather not do that.

I have a similar display and there is a resistor in series with the backlight led(s). That smd-resistor has 330 printed on it. For smd's that means 33 multiplied by (10^0) so 33 multiplied by 1 and that is 33 ohm, NOT 330 ohms. With a 330 ohms series-resistor the led-current will only be a one or two millilamps, much too little for the backlight.

So if you use a 33 ohm resistor the BL-led-current (in my situation ) is 48 milli-amps. If you drive the leds without any current limiting resistor from 5 volt, that will not be good.

There are several SMD resistors on the back, but the PCB is more than one layer so I can't trace it. Is the backlight the same as the pixel light? Because there are separate power pins for both. Should I just try a 33 ohm resistor?

Squirt_5432: There are several SMD resistors on the back, but the PCB is more than one layer so I can't trace it. Is the backlight the same as the pixel light? Because there are separate power pins for both. Should I just try a 33 ohm resistor?

I don't know what you call pixellight, as far as I know pixellight is a software package for 3D rendering. LCD displays (like this 12864) have only one lightsource, the LED-backlight, that is separated from the rest of the display-electronics. And it is usually located on a outerside of the row of pins. Pin 19 & 20 but I can only be sure of that if you have a picture of the backside of the display. There is also a pin for powering the processor and segment drivers and there is a pin for contrast setting. Probably you have a problem with the contrast setting, if that is not stable , it can make the pixels fade away.

Ohhhhkay yeah it's definitely the contrast that I'm having trouble with. I just didn't know what it was called. So should I be using a resistor for that?

Squirt_5432: Ohhhhkay yeah it's definitely the contrast that I'm having trouble with. I just didn't know what it was called. So should I be using a resistor for that?

Isn't there a very small variable resistor on your display? That is needed to set the contrast. If there is no variable resistor you need to connect an external varible resistor (aka potmeter) . One wire to ground, one wire to vcc and the middle wire to Vo , (usually pin 3) .If you don't have a potmeter you can try to connect Vo to Vcc (5V) preferrably with a resistor. If you have a potmeter then watch out because if you connect the middle wire on the wrong pin of the potmeter, the potmeter will get damaged.

Read this post , it is about the same display and problem. http://forum.arduino.cc/index.php?topic=164537.0 Or even better , search this blog, in the top there is a search windoe. Fill in " 12864zw lcd contrast " and read several links, than you get more answers than i can give.

Indeed there is no variable resistor on the back; I noticed that when I first got the board and was learning how to use it. I will get another pot and hook it up, as well as look at the links. Thanks so much!