This article shows a single-phase energy meter solution using the MCP3909 Dual Channel ADC and the PIC18F25K20 8-bit microcontroller. The current sensor is a 200 µΩ shunt. To improve the low current measurements, the value can be increased to a larger resistance and the meter would require calibration at this lower current. The shunt used in this application note is a model that is connected to the circuit through screws on the meter case. The meter PCB has a footprint for an SMD Shunt and the two large through hole pads are available for high current wire soldering.

For systems that require more than local display or monitoring, a second circuit is available for remote monitoring through USB. On the same PCB, there is also a USB circuit, isolated by the meter circuit with optocouplers. This circuit uses the 8-bit PIC18F14K50 microcontroller with USB. The USB circuit is powered from the PC. The firmware given has the USB set up as a virtual COM port with a 19200 baud rate.

The MCP3909 is an energy-metering IC designed to support the IEC 62053 International Metering Standard Specifications. It supplies a frequency output proportional to the average active real power, with simultaneous serial access to ADC channels and multiplier output data. This output waveform data is available at up to 14 kHz with 16-bit ADC output and 20-bit multiplier output words. The 16-bit delta sigma ADCs allow for a wide range of IB and IMAX currents and/or small shunt (< 200 µΩ) meter designs. The integrated on chip voltage reference has an ultra-low temperature drift of 15 ppm per degree C.