Measuring AC Main Supply Voltage with Arduino (2)

   In article named Measuring AC Voltage with an AC to AC power adapter from OpenEnergyMonitor I found a interesting solution for measure AC voltage.
   Schematic is

   I use EmonLib library like in article:

   On DSO I see on R1 resistor

and at A2 input of Arduino board (on R4 resistor):

   I use an LED display with 8 digit 7-segment drived by MAX7219 (I present on article namend Modul de afisare cu 8 cifre LED din 7 segmente fiecare controlate de MAX7219

   I use some configuration for LedControl library (dosc at The Arduino LedControl library):

   Test schematic is

   I write main_voltage_emonlib_1.ino sketch and upload in Arduino board:

  I made main supply voltage measured with Arduino (2) movie: