This is a project I use to measure the power consumption in my appartment in real time.
My apartment has a power service box with an LED that blinks 2000 times pr kWh. I use the nRF52's Low power comparator to count the number of pulses and a timer to measure the time between them. With these values I can calculate an approximate value of the instantaneous power consumption and the total energy consumed. I also use the ADC to measure the battery status of the device. The data is simply put in an advertising packet and advertised at a slow interval.
