# Hooking up an 8x8 LED board

I recently bought this 8x8 LED board from geeetech which came with this datasheet. I'm new to programming so I bought this board to "figure it out" but now I'm running into issues I don't understand.

For starters, I've noticed that I can only get one color value out of an individual LED. By hooking up pins 9 & 1 I assumed I would get a magenta looking color but I only get solid red. If I unplug pin 9 then I get solid blue. What am I missing here?

Lastly, I accidentally already blew two of the RGB LEDs by hooking up straight to a 6v source. So now I'm using a potentiometer to control resistance (rather than a resistor), is this okay?

Let me expand on Majenko's answer. First, an example. Get 3 330 ohm resistors. Connect pin 17 to +6 volts. Now, with one end of a resistor connected to your 6 volt -, touch the other end to pin 9. You should get a solid red. Now touch the end of the resistor to 28: you should get a solid yellow. And touching the end to 1 should give you a solid blue. Now connect another resistor to 6 volt -. If you simultaneously apply one resistor to pin 1, and the other to pin 9, and you should get magenta. Likewise, if you connect pins 28 and 1 (one resistor to each pin) you should get green. Pins 9 and 28 should give you orange, and if you add a third resistor to the setup, connecting all 3 should give you white (more or less).

For 6 volts, 150 ohms should be the smallest resistance you use on green and blue, and 200 ohms on red. If you're going to use a pot, it is best if you connect a 200 ohm resistor in series with it, just so you don't accidentally crank down the resistance too much.

And how do you get the resistances? Look at the data sheet. All the LEDs are rated for a maximum of 20 mA. With 6 volts, you subtract the LED voltage (1.9, 3, and 3 volts for R, G, and B), to get the voltage across the resistor, then divide by .020 (20 mA) tog get the resistance. The is the classic use of V = iR, or in this case R = V/i.

• I marked this as the answer because the walk through is very helpful, thanks! – Jacksonkr Jan 24 '15 at 21:13

The problem you are experiencing sounds like your lack of knowledge on how to wire up LEDs.

Every individual LED needs its own separate resistor. Running two LEDs in parallel with different forward voltages (such as a red and a blue) will mean that only one LED operates - the one with the lowest forward voltage (the red one in this case).

If you want to use a potentiometer instead of resistors then you would require one separate potentiometer for each and every colour of each and every LED you want to light up.