I have built the 4 layers of 4x4 LED's and connected them up.

My question is what transistor should I use. I know that only one layer will be on at a time and the max current draw will be 16*20mA = 0.320A

I want to use a NPN as my layers are common cathode so the transistor will connect the layer to ground.

So what specs should I be looking for, I know Ic needs to be greater than 320mA

I am looking at a 2N4401 at the moment. Would this suit? If not why

I will have the Anodes driven by 2 74HC595's. An AVR will be doing all the hard stuff.

up vote 2 down vote accepted

In don't know what you mean by 4 "layers". Layer makes no sense in this context, and a cube has 6 sides, so this doesn't add up. I'll therefore assume the question is about multiplexing 4 sets of 16 common-cathode LEDs.

Yes, a 2N4401 and many other NPN transistors will work for the low side switch. You will need one of these for each set of LEDs, which is apparently one set for each of the 4 faces of your strange cube. The anodes of each position can be tied together since only one set will be on at a time. This leaves 16 anode connections to switch. Each of those needs a series resistor so that the current per LED is 20 mA.

  • How about using matrix drive? Tie anode connections together going down the matrix; cathode connections across. A single high-current variant of the 595 can then be used to drive each layer. – Bitrex Mar 25 '12 at 15:01
  • The cube uses 4 layers of 4x4 grids of leds, giving a total of 64 addressable led's. Thanks I will order some 2N4401's to get the job done – Ashley Hughes Mar 25 '12 at 20:27

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