Grace Copplestone committed Aug 14, 2017 1 2 3   Sam Calisch committed Aug 14, 2017 4 This is documentation for an energy monitoring device built around the nRF52832 system-on-chip from Nordic. It includes a 2.4 GHz BLE-enabled radio transceiver, a Cortex M4F microcontroller, and a host of hardware peripherals. The device is capable of extracting current and voltage waveforms from a standard wall power plug without contacting the mains power. The current is measured inductively, as a mild steel flux guide channels magnetic flux through a sensitive hall effect device. The voltage is measured capacitively, as the flux guides couple with the conductors in the plug. Measuring both quantities allows us to separate active from apparent power, measuring the real power used by an appliance plugged through our device.  Sam Calisch committed Aug 14, 2017 5 6 7 8  bc832-watt/ includes source files for a PCB built around the BC-832 module (containing the nRF52) from Fanstel.  Sam Calisch committed Aug 14, 2017 9   Sam Calisch committed Aug 14, 2017 10 11 12  This device produces around 0.1 volts/amp out of the sensor (or ~1 mV per Watt through the plug). The nrf adc has a +-0.6V reference, 4x gain, and 12-bit conversion, which might resolve 100mW (maybe finer with oversampling). Certainly not precision measurement, but good enough for monitoring appliances.  Sam Calisch committed Aug 14, 2017 13 14 15  The nRF52 radio+microcontroller draws 5mA in transmit and receive, so it could operate well within the specs of a coin cell, or harvest from the power line (say, using http://www.linear.com/product/LTC3588-1) to charge a capacitor for power. Below, we see the flux guides registered into pockets on the pcb.  Sam Calisch committed Aug 14, 2017 16   Sam Calisch committed Aug 14, 2017 17   Grace Copplestone committed Aug 14, 2017 18 19 20 21 22 23 24 25 26  ### Power requirements The nRF52832 draws 5mA peak @ 3.3V The Hall Effect Sensor draws xmA @ 3.3V Assume whole device runs at peak load for 10% of the time  Grace Copplestone committed Aug 14, 2017 27 28 29 $$P=IV=5e-3*3.3*0.1=1.65mW$$