[BASIC] Can i use only i/o pins to light a led?

Other Hardware LEDs and Multiplexing
1

Hi
Can I plug a led in pin 3 and 4 (with resistor) and set 4 to LOW and 3 to HIGH, will this light up the led or is it bad for the Arduino if you use an output pin as ground? And if i put them both tot HIGH, will the led go out?

Thank you!

3

Thanks!

4

Not sure why you would want to do this. You could do it if you had a tricolour LED with only two leads but otherwise there seems to be no need.

Do you think you are running out of ground pins? We have seen beginners think this is a problem as they don’t realise you can connect more than one thing to a pin.

5

Grumpy_Mike:
Not sure why you would want to do this. You could do it if you had a tricolour LED with only two leads but otherwise there seems to be no need.

Do you think you are running out of ground pins? We have seen beginners think this is a problem as they don’t realise you can connect more than one thing to a pin.

It's because I didn't understand why you don't use a ground in a 8x8 ledmatrix and only i/o pins so i think I get it now? (I understand that you can't just put ground on everything on one side, every led will go on during the multiplexing) Or am I missing something?

6

Yes, 8 pins with current limit resistors to drive anodes high, and 8 pins to drive cathodes low.

Multiplex with one high and one low at a time, cycle thru all 64 LEDs.

You can also drive 8 anodes high, but then you need a transistor or a part like TPIC6B595 to sink current from all cathode in parallel, the so display can be brighter.