Running A Led Of Port D6


Hey guys.

I have a couple of general questions regards running LED's off a digital port.

1. I hooked up a 3V LED to the signal and ground pins on D6 on my v4 earlier today, made a little digital on, sleep 5 seconds, digital off script to test it but all it would do is very quickly flash once. I changed it over to port D12 and it worked fine. Any reason why D6 didn't work? The port is fine as I tested it with a servo. I was just wondering if it's because D6 is also a UART port as well and this may have caused the issue.

2. Any ideas if I could power a set of 20, 3v fairy lights off the V4 signal and ground pins? I lent my multi meter out so I can't test the amp output of the LED's. They normally run off two 1.5v AA batteries. Could 20 bulbs be too much?

Thanks. Smile


How many mA is that led drawing? Anything over 20mA would be bad for the digital port... I have an ezb that has ports that will drive a servos but won't do digital on/off.... But that was my fault as I think I blew those ports...


Maybe you could be right.. the fact that D6 is the receive of UART port 1 may make it behave different from other regular ports....


Hey Richard. I was (and still am) unable to test the mA from the single LED as I don't have my meter right now. It's interesting about the UART possibility. I wonder if anyone else has had similar issues with the digital UART ports?


I have a bunch of LEDs. I'll try d6 vs other ports tonight or tomorrow night.

As far as amps, even my big superwhite is only 20ma. I am sure you could run 20 off a v4. You should be able to run them all off a single port (wired in parallel, so the voltage stays the same).



@Alan... 20 if you use 20 ports... I don't know of any LED that draws only 1ma.. Each digital pin can only supply 20mA... You draw more than 20ma from the signal pin and you risk losing the port... So one LED per port...

I have a bunch of these 2 wire 20ma leds I got off of eBay... I only drive one per port.... You can buy leds that use power from the + power pin and the signal to drive it from the digital pin... I have some of those too, but they are 3 wire LEDs... They consume more than 20ma but they get their power from the + pin so it doesn't matter how much power they consume...


Right..... I was confusing the VCC+ with the signal. Thinking 5 amps would drive 250 20ma LEDs, but no, not on the signal pins.

Still, little fairy light LEDs will be way less than 20ma, so multiple per port, but need to measure more carefully.



Wow, this was only ment to be a general question but I'm kinda glad I asked now, as I don't want to kill one of my ports and glad I didn't try hooking up the fairy lights first. So Richard, you reckon hooking up a 20 bulb strand to one port is not a good idea then?

@Alan. In regards to the D6 issue, it will be interesting to hear your results when you try it.


@Steve G... Not if you are powering them from the signal pin... Guaranteed your light strand is pulling more than 20mA.... My advice is don't hook them up until you actually determine how much current they are drawing...

I'll try too (D6 and a 20mA led) tomorrow, Steve... Will let you know...


Cool. Thanks guys. Smile