To measure the battery voltage with the BBC micro:bit follow these steps:
1- Create a program with an Analog Read Pin P0 block and upload it to the micro:bit. This puts P0 in analog input mode.
2- Connect a jumper from Battery Voltage Monitor on the Solar Battery to the P0 input on the micro:bit.
3- Create a program that will loop on analog read P0 and printout the results. The reading will be between 0 and 1024
4- The battery voltage will be equal to (( 3.19V ÷ 1024) x 2.4 x reading). For example a 3.7V battery will give a reading of 495.
Notes: 3.19V =( micro:bit A\D reference voltage) = (Solar Battery Voltage 3.3V – drop in the micro:Bit regulator). If the battery is discharged below 3.45 volts, measure the voltage on the micro:bit 3V terminal to determine the correct value.