External Power Supply Matrix

Hi all, I'm trying to create a matrix of banks of led's. These banks of led's are 6 led's hooked up anode to cathode that use up 2 volts per Led (12v per bank) with a 1ohm resistor at the end of the bank.

Now I can't use the Arduino to supply the voltage, but I can use it to switch the matrix on and off. I'm using an NPN transistor at the ground end of the bank, but I do not know what transistor to use at the source of the bank to do the on/off switching. I've tried a few things, I even blew out my port #3 because of the 12v going to that pin oops!!! :o

Can someone please help me solve this problem I'm having (I'm new to electronics and just want to tinker around).

I hope this all made sense.

Thanks in advance.


You'd only really need the transistor at one place in the circuit. Since current only flows when there is a complete path, one break is enough to prevent it moving.... The short answer is that it should work with only your NPN transistor before ground.

... Just make sure you connect your arduino pin to base, and connect both grounds. (:

The thing is I want to create a matrix out of these banks. I have 44 banks all together and I want to create a matrix of 4x11 (something like that) and use the code provided in the sample (direct drive 8x8 matrix). I'm sure you know that a Matrix is controlled by both the start of the path and the end of the path.



hmmmm, what about using one of those ic's that are shift registers... I'm not sure how many volts you can pump into these babies, but you might be able to get away with inputing 12v total to make your led's shine brightly...

the arduino only sends it directions, you don't need to hook up the arduino power and ground to it, i believe external voltages can be given to it, this way you can control multiple outputs with the correct voltages!

I just checked the Max7219 and it can only supply 6v, only half of what I need.

I found this chip on digikey http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=AD8240YRM-ND. I think if I were to use 4 of those for the + side of my matrix and 11 transistors for the - side then it might actually work. It even does PWM!!!

Could anyone confirm this chip to do what I need it to do. I'd rather someone confirm before I start spending some$$$ ;)

Thanks for your help!


np, im not a datasheet type of guy, hopefully you can get one of the pro's attention, or pm one of them, but good luck wit this project, and i hope i helped you!

a 1 ohm resistor? Do you have a diagram or pictures of how you have this setup connected? 1 ohm is basically the same as no resistor at all.


Why not use a few 7219's? You can chain them together. Or a few tlc5940's.

Why not use a few 7219's? You can chain them together. Or a few tlc5940's.

Because they do not supply enough voltage for the matrix I want to build! I suppose I could unsolder all 250 or so of my led's that I soldered personally and hook them up to 7219's daisy chained, but I'd rather not!

a 1 ohm resistor? Do you have a diagram or pictures of how you have this setup connected?

I dunno if I said that in this post or not but I don't know much (or anything) about electronics so I got my 1 ohm idea from http://led.linear1.org/led.wiz and I plugged in these values (Source Voltage = 12v, Diode Forward Voltage 2V, Diode Forward Current 30mA, # of LED's 300) and up came that 1 ohm resistor... so I followed instructions! You'll also be able to get the schematic of it.

What am I using this for?? Well it's for a poker table. See image below, the little red dots are all 2x5 rectangle LED's

And here is the schematic of what I want to do with the big ???? where I'm having problems! BTW, I drew up that schematic from scratch in Illustrator... so if there are errors, please forgive me!

I hope this makes it much clearer of what I'm attempting to do. I don't know if I'm past the tinkering stage and going into obsession, but that's ok, I'm having a blast doing it!

Thanks for your help


You need a resistor in the base circuit of the transistor. http://www.arduino.cc/playground/uploads/Learning/relays.pdf

One at a time you can manually apply +12v to the top row and switch on and off the pins on the left side as a test. A zener on the input to the arduino of 5.5v would protect it but you'd need one for each IO.

You should be able to use transistors for the top pins. 12V to collector emitter to array , base to resistor and resistor to arduino.

For later:

You could use some IO expansion as you've used up most of your IO.

You can get 16 outputs by using two 74HC595 chips. Your circuit needs 15 IO ports which will drive transistors to switch the voltage you want to where you want. You hook the outputs of the 595 to a resistor and then to the transistor as stated above.

Look at the tutorial for ShiftOut http://www.arduino.cc/en/Tutorial/ShiftOut

You will now only use three arduino IO pins.