Use 64 digital pins

Hello I just want to know If it is safe to use all of the digital outputs to control led’s. I have Fez Panda 2 board. I’m planning to connect all of them directly on board.

I think that depends on what you mean by “control”. You definitely shouldn’t try and power them all through the pins. You’ll want to use a transistor at minimum to control power to the LEDs. I’d look at multiplexing them. You can control all 64 using only 16 pins using multiplexing.

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I’m aware of multiplexing , but then I would need to switch on and off LED’s and rework the code. I just want to know how many diodes I can turn on at the same time without damaging the board.

See this thread.

BTW, welcome to the forum!

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As many as you have I/O, as long as you don’t exceed either any one pin’s maximum current rating, and don’t exceed the device’s maximum current rating.

As Ian said, you’ll certainly need at least a giant pile of transistors to do that, or some external mechanism, such as LED drivers or whatnot.

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I was going to go a similar route but I ended up using four 74HC595’s to drive my LED’s on my project. Figured it would be safer to draw current from the 595’s rather than the FEZ. That was for 32 LED’s in total, you would just need to chain more chips to add more outputs. Also, only needed 4 pins from the Panda to daisy chain the chips and can now reuse it on any future project :slight_smile:

Edit, GHI has a pre-built module called the MaxO.

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Thank’s for replies I think I’m going to start with 8 transistors on cathode and 8 on anode with external power supply . Common use for 8x8 LED as I saw on Arduino’s.
I studied that: [quote][/quote]

If I want to turn LED lets say row/column:1,1 in matrix and 2,2


LED11.StartBlinking(50, 200);
LED22.StartBlinking(50, 200);

Then it shoudn’t turn on LED’s in position 1,2 and 2,1?
Is that the aproach I should be using? I have curently only two -BC548B transistors so I can’t test on matrix.

@ primzi - I’ve found that using an array of OutputPort objects is a good way to deal with multiplexed LEDs. You can see my LED cube driver here for an example:

There’s probably plenty of opportunities for optimization if you need to switch them very fast but this was plenty fast for my needs.

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