Running different coloured LEDs from one output pin

G’day

In a nutshell a student is using a single output pin to run LEDs of 2 different colours. There are 3 yellow LEDs connected in parallel and 2 red LEDs connected in parallel. The 2 parallel circuits are soldered into one wire that connect to the output pin. The 2 negative lines are soldered together and, via a resistor, connect to the negative rail on the breadboard. The LEDs didn’t work so I suggested separating the two negative lines and using a separate 1k pot on each line. I also inserted a test LED on the breadboard for each line. Both test LEDs were working fine. I plug in the red LED line and it works. I plug in the yellow LED and it works. Plug in both and they don’t work. Also noticed that when the yellow circuit was plugged in, the red pot affected the yellow LED. There seems to be some feedback happening but not sure exactly what is happening. Can anyone please explain this?
I have thought of separating the red and yellow lines for different pin outs but this would mean using the 0 and 1 pins as the others are used. Can this be done? Am using Uno and there is only a stepper driver in use as an add on module.

Thanks

Edna

Are A0 to A5 used? Those are digital pins also, D14 to D19.

You are likely drawing too much current for the IO pin with the LEDs in parallel.

0 & 1 are the serial lines that also connect to the USB chip. When Rx is an input, a weak pullup resistor is provding the high signal - it does not support the 20+mA output that a normal output pin would have (up to 40mA, or when the pin overheats and fails).

CrossRoads:
Are A0 to A5 used? Those are digital pins also, D14 to D19.

You are likely drawing too much current for the IO pin with the LEDs in parallel.

0 & 1 are the serial lines that also connect to the USB chip. When Rx is an input, a weak pullup resistor is provding the high signal - it does not support the 20+mA output that a normal output pin would have (up to 40mA, or when the pin overheats and fails).

Ah, from the writing on the board I assumed that A0 to A5 were analog input only. That frees up some more pins. Yes, it probably is exceeding the individual pin current rating. We do have an external power supply for the servos and steppers but didn't think that would be required for the LEDs with their low current draw. Will rewire via the new pins and adjust the coding. Thanks :slight_smile: