/diy/ - Do It Yourself

>>1787920
arduino isn't engineering, so all that advice is still good :^)
in the datasheets of MCUs and external chips you will usually find a section of characteristics which lists, among many other things, current consumption of the device under a number of different specified conditions. I looked up the STM32F072, which has some nice features (USB DFU bootloader, crystal-less USB, good power management, cheap, available), picrelated
the STM32F072 draws 5.6mA worst-case executing code from Flash with all periphs enabled. the nRF8001 Bluetooth transceiver pulls 20mA total, typical, when the receiver is on 100% of the time (implausible worst case). there's probably several hundred µA on the board in analog portions of the F072, GPIO pins, leakage and otherwise not being accounted for, so let's just round up 20mA+5.6mA = 27mA which we now divide into 180mA for a ballpark absolute minimum run time of 6.66 hours on battery. actual power usage depends on your Bluetooth profile and configuration info. also there may be more power-efficient Bluetooth radios out there
if you wanted to, you could also look at sleep mode consumption which, for the F072, is about <1mA with everything off, and <3-4mA with everything but USB on. another table on p58 (not shown) shows the analog Vdd current consumption, which is approximately 10% additional, not more than 354µA in any case. the nRF8001's input power can be cut with a MOSFET to zero its power consumption
note, zero fucks to give about the high power consumption while the USB peripheral is active because you would probably not be discharging the battery at that time anyway

>>1787988
good point, bypass caps should be very close to the loads they are to serve. inches matter