My Arduino Uno pins will not power a strand of four christmas lights.

Hey, I'm not sure if this is the correct place to post this. If it isn't, can someone move it? Thanks.

I'm working on a project involving four separate strands of Christmas lights, each strand containing four lights. I checked the strands with both the 5V and 3.3V pins on my Arduino Uno and they all work. I plugged them in to pins 11, 10, 6, and 5 and wrote code to power them on and off as needed, but they won't turn on. I tried using digitalWrite() and analogWrite() and tried it with only one Christmas light hooked up at a time, but nothing I've tried works. I know the pins they're hooked up to work, I've tested them with LEDs, so what gives? I'm guessing there's an obvious reason why this isn't working, I'm new to electronics. Thanks for your help... :slight_smile:

Were you trying to drive the entire string just from an Arduino pin, without using a transistor?

Your Arduino may already be irrepairably damaged.

@AWOL
No, I know can't control an entire strand of Christmas lights from a single pin without a transistor! I cut a large strand of lights into smaller strands with only four lights each so I'm only powering four Christmas lights from each pin. I tested the pins again to make sure they're still working and they are.

----- = wire
0 = light

normal strand of lights (not what I'm using):
----0----0------0------0-------0-----0-----0------0-----0-----0-----0-----0-----0---- (and so on...)

strand of ONLY four lights (what I am using in my project):
----0-----0-----0----0----

This SHOULD work, but does not:
(pin 11)-----0----0----0----0----(GND)

This DOES work:
(5 volts)-----0-----0----0----0----(GND)

I've tried using digitalWrite() and analogWrite() on the pins with lights, but they will not work!

Unless the strand includes resistors, then even one led would not work for very long...

Why "SHOULD" it work?

What kind of lights are these, exactly? Those small incandescent types? LEDs? Both are wired in series, by cutting the strand, the circuit has been opened, did you do anything about that? Even so, I doubt it'd work, with four lamps, each needing ~2V, the Arduino cannot drive four in series. If they're incandescent, I'd also be worried about the current requirements. Arduino pins can only supply 20mA and those lamps may require more. I might go read up on some basic electrical concepts.

I took a single Christmas light off a strand of lights. I can connect one end to ground and another to a pin and have it go on and off properly, but if I have a resistor in the circuit, it will not work! This isn't a problem or anything, I'm just curious why it's doing this. It doesn't make any sense to me. Thanks.

It doesn't make much sense to me why you'd open a new thread on the same subject as an existing thread, so I merged them.

Are they LED or incandescent bulbs?

B3nj1771:
I took a single Christmas light off a strand of lights. I can connect one end to ground and another to a pin and have it go on and off properly, but if I have a resistor in the circuit, it will not work! This isn't a problem or anything, I'm just curious why it's doing this. It doesn't make any sense to me. Thanks.

None of us can have a clue without more details about the lights you're working with. Nor is "a resistor" specific enough. What is its value?