I want to measure the battery voltage on my arduino pro mini (3.3V version), which runs from a Li-ion smartphone battery (max 4.2V).
I used the typical voltage divider setup with R1 = 5.6M and R2 = 2M, because of this formula:
// ((R1+R2)/R2)*1.1 = Vmax = 4.2 Volts // 4.2/1023 = Volts per bit = 0.004105572 float batteryV = sensorValue * 0.004105572; int batteryPcnt = sensorValue / 10;
But it doesn't seem to work.. currently it is giving me a voltage of 1.28V, but my multimeter is measuring 3.86V.
What am I doing wrong?