This WiFi enabled three channel AC current/power meter uses the popular SCT013 Series Split Core Current Transformer (CT) manufactured by YHDC and commonly found on AliExpress, Alibaba and Ebay.
The power meter doesn’t sense the mains voltage, and hence makes an assumption of the power consumption based on a defined line voltage. However, in many circumstances this is good enough and reduces the requirement for a voltage transformer and connection to the mains power supply.
WiFi connectivity is provided by the ESP8266, an extremely low cost, highly integrated WiFi SoC based on the Tensilica L106 32-bit RISC processor.
It would have been elegant to have used only the ESP8266. After quick evaluation of marketing collateral, it became apparent the ESP8266 only had a single 10 bit ADC with a 0 to 1V input range, peculiarly named TOUT. However the bigger drawback was the power consumption.
With the addition of a PIC24F microcontroller, we can achieve not only multiple current sensor inputs, but at a higher 12-bit resolution. The ADC inputs accept analog voltages up to 3.3V (rail).
The other big advantage is the PIC can continually sample the sensors, and accumulate power consumption with the ESP8266 powered down to save power. It can then periodically, wake up the ESP8266 to transmit accumulated power consumption, minimum and maximum currents over the past period etc.