What works:Supplying VIN (regulated input) with
4.9v works for me. After the regulator the "5v" power supply ends up running at
3.48v and the digispark seems pretty happy with that.
What doesn't work:Things started to look a little glitchy when the power supply dropped down to 4.3v on VIN and 2.95v on the "5v" connection. It seemed as though the clock speed of the digispark had become unstable enough that my LEDs weren't reliably communicating with it anymore and were missing some animation frames. When the voltage reached
4.1v on VIN and
2.62v on "5v" pin the whole thing froze up and seemed to completely fail.
Why should I care?You can run your digispark projects off a 9v battery hooked up to vin and ground and it's going to run for fricking ever. You can use
rechargeable li-ion 9v's and the protection circuit in the battery will shut it down before the voltage to the digispark reaches a point where things start glitching out. A nice clean death.
My test rig?I have a digispark with VIN and Ground connected to a disposable 9v battery, and I've connected four florapixels cycling through rainbows so I could see the microprocessor was still running. When I check it with my multimeter the whole thing seemed to be drawing about 80ma, about 20ma of which seemed to be used by the digispark!
Ways to make the digispark use less power?The easiest thing is to remove the little power indicator LED located right beside the VIN pin connection. If you want to take things further you can
underclock the CPU. You can even break the USB connectivity by removing the 1.5kohm USB Pullup resistor for a saving of about 3ma. The 1.5kohm pullup (R3) is located on the corner furthest from the power LED.
The best way is probably to just buy some raw
attiny85-20PU chips and turn one of your digisparks in to a littlewire, so you can upload sketches directly to the raw chips without having to disable any other bits of random hardware.
Should I worry about anything else?The chip clock speed goes up a little as the voltage goes down. The clock speed also goes up with ambient temperature increases when not syncing to a computer's USB port (which calibrates the digispark's clock at boot, and if you're using a digispark usb library usually keeps recalibrating it in the background too). You should also never upload sketches to a chip which is (somehow) running on less than 4.5v. Running the digispark out of spec like this is a bad idea when it needs to erase or write flash - it could glitch out and brick itself.
TL;DR:I think we can safely say the digispark's VIN input can take voltages down to
6.0v without putting the digispark out of spec. Voltages lower than that seemed to work fine too for some applications. Want to make it official, digistump?
