Pk-RMS WATTMETER:
PK-RMS is a low price high speed programmable wattmeter capable of measuring voltages, currents, powers and frequencies 50 times per second. Readings can be saved to microSD in real time (csv format).
This first prototype is based on an "Arduino Nano Every" development board (ATmega4809).
The MCU's internal 10bit ADC samples the attenuated voltage, coming from the voltage divider, the current, coming from the CT, and the 0.6V reference voltage.
The ADC uses the internal 1.1V reference and since it can't measure negative voltages the AC inputs needs to be offset by the 0.6V reference (close to half of 1.1V).
The meter synchronize to the AC input by counting the zero crosses. Depending on the selected speed, it will wait for a certain number of zero crosses, before outputting a reading. If DC is applied, no zero voltage cross is detected and, after a certain time limit, the meter will output a reading and start a new sampling cycle.
Published: 2023-04-01, Last edit: 2023-10-13