Is there any documentation for the maximum mA output on these?
I'm looking to run a bluetooth module and power 8 RGB leds. Can this board handle that? I'd also like to run power through a usb backup battery brick, but I'm worried about running 5V @ 1A. If I have to I'll run 3 AA batteries, but I like the idea of an external usb battery pack so i could also charge other equipment.
The 32U4 seems to have similar limitations to the Atmega328. That is, absolute maximum of 40 mA per pin, and recommended 20 mA. Also a total power consumption of 200 mA for the whole chip, and a limit of 100 mA for groups of pins (see the datasheet). Sounds very similar to what I summarised here:
Through the USB port? That looks OK to me, but be warned you can't draw an amp through it. If you mean the power supply can supply an amp, that's fine. The board will take what it needs.
If your 8 LEDs are within the limits I mentioned above it should be OK.
again, thank you for the info. i wasn't expecting to draw 1A of power, just making sure it wouldn't damage the board running that much through the usb.
at full white the RGB LEDs draw 60mA. sounds like i might have a problem with too much draw on certain colors.
60 mA per LED? And you have 8? That's close to the limit for a USB (I think that maxes out at 500 mA), and is definitely too much for the processor. Some switching transistors (MOSFETs) will be in order here.
Yes that was what I was suggesting. Take the external power and switch it with a MOSFET (per LED). Then the controller just has to have enough power to turn the MOSFET on. However 8 RGB LEDs will require a few MOSFETs (24).
You might be better off with a TLC5940 or similar driver, which is designed to drive 16 LEDs at constant current. This will save getting a lot of resistors. For 24 LEDs (3 x 8) you might need two of them, unless someone else has a better idea.
Another approach could be to multiplex the LEDs so they aren't all on at once.
the external battery pack i'm eying has two outputs, one will be used to power the board/bluetooth and the other will be used to power the LEDs. in the future i might power the LEDs off of a simple AA battery pack to free up the extra port on the usb battery pack for phones or other add-ons. thank you very much for walking me through this.