Arduino AC Voltmeter Project with Code and Circuit Diagram Working of Arduino based AC Voltmeter: 1. Step down voltage is obtained on l.v side of transformer which is suitable to use across normal power rating resistors. 2. Then we get suitable voltage value across 4 resistor. Maximum voltage that can be measured is found by simulating this circuit on proteus (explained in simulation section). 3. Other AC Voltmeters - Tutorialspoint The circuit diagram of true RMS responding AC voltmeter is shown in below figure. The above circuit consists of an AC amplifier, two thermocouples, DC amplifier and PMMC galvanometer. AC amplifier amplifies the AC voltage signal. Two thermocouples that are used in above circuit are a measuring thermocouple and a balancing thermocouple.