Led array power

Hi. I want to build a 6x4 array of IR leds (1.2-1.4 vf, 20 mA) and I want to turn it on an off from either an Arduino UNO or a nano. I was thinking of having 6 parallel strings of 4 leds in series with their respective resistor each. If my calculations are right, that would be 120 mA. Can I hook that up to a digital pin of the Arduino or do I need to externally power up the leds and control the on/off with a relay?
Thank you

I'm not quite understanding your setup. But you cannot source or sink that much current directly from an Arduino pin. Use the Arduino to control one or more transistor switches.
S.

The easiest would be to power the LEDs from an external power supply, A Power Supply the Arduino Does NOT make. Connect the ground to the source of a N-Channel logic level MOSFET rated at a few amps (then no heatsink required). Connect the Arduino pin to the gate of the MOSFET. It would be best to put a pull down resistor directly to the Arduino pin, 10K would be a good value. The Drain of the MOSFET is your output and the positive comes from the external power supply. Be sure all grounds are connected. This is called a low side driver.

The spec for the 328P

Safe maximum per pin 20mA, absolute maximum 40mA.
Maximum per port 100mA.
Maximum through Vcc and GND 200mA.

IR LED drivers.

What power source are you using? A 5V supply (USB?) you don't have enough voltage to drive four LED's in series. That would require over 5.6V (4 * 1.4V).

If you only have 5V you could use three LED's in series. An Arduino UNO/Nano pin can easily drive a 20 mA load so you could power all 24 LED's from 8 pins without any additional hardware.

johnwasser:
If you only have 5V you could use three LED's in series. An Arduino UNO/Nano pin can easily drive a 20 mA load so you could power all 24 LED's from 8 pins without any additional hardware.

But you have to choose the pins carefully; e.g. all on pins 0..7 exceeds the maximum for a port (100 mA). So e.g. pins 4..7 and pins 8..11

This topic was automatically closed 120 days after the last reply. New replies are no longer allowed.