Measuring AC Main Supply Voltage with Arduino

   If you need to measuring AC main supply voltage with Arduino must made some calculation.

   I use a simple schematic:

   I can directly measure the DC voltage on R1 resistor. I use internal reference from Arduino Uno board (compatible board with ATmega328 microcontroller) so maximum value for U2 can be

U2 = U1*(R1+R2)/R1 = 1.1*(1+22)/1=25.3V

  AC voltage U1 so DC voltage U2 = U1*1.41-Udiode

  If we put value in equation

U1 = (U2+Udiode)/1.41

because I use trafo U0 = k * U1.

  For tests, I use a trafo imprinted 220V/2x12V 200mA but if I measeure voltage from secondary coil

I found 11V when main voltage is 220V, so k = 220/11=20. I use an 1N4007 diode and Udiode=0.65V.

  I use an LED display with 4 digit 7-segment drived by TM1637 (who I present on base blog in article named Afisaj cu 4 cifre controlate de TM1637 si Arduino and sketches are at https://github.com/tehniq3/TM1637-display):

   Schematic for display put on Arduino Uno is:

   I write main-voltage_0.ino sketch and upload in Arduino board and I made a movie named main supply voltage measured with Arduino