If you're pulling a lot of current to drive whatever the relays switch, be careful to keep the power wires away from the Nano.
I'd be inclined to have those relays switching LEDs with a separate power supply to start isolating the problem.
If you're pulling a lot of current to drive whatever the relays switch, be careful to keep the power wires away from the Nano.
I'd be inclined to have those relays switching LEDs with a separate power supply to start isolating the problem.