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  • Low-Cost Shunt Power Meter using MCP3909

  • Created: May 18, 2016

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This design features MCP3909, which is an energy metering IC with SPI interface and active power pulse output. This reference design only shows the power meter analog circuit. As it name suggests it has 200uΩ shunt resistor, which is used as a current-sensing element. The value of this resistor can be increased to improve the low current measurements. This design supports IEC 62053 international metering standard specifications. An LCD is used to show the RMS current and RMS voltage (URMS and IRMS) on the first row, and the Power Factor and Active Power on the second row.

The communication between the MCP3909 and the microcontroller is through an SPI interface. In this design, the MCU receives the current and voltage samples from the MCP3909's 16-bit ADCs. Inside the microcontroller, these samples are processed in order to get the URMS, IRMS, power factor, active power and energy accumulation. After the last byte is received, the MCU starts to calculate the phase for all the power quantities. Each data transfer causes an SPI interrupt to begin this calculation on each sample. The user can easily change the meter firmware to send information from the meter to PC for different tasks, such as accuracy evaluation, calibration, among others.

This reference design is applicable in a wide variety of applications that require power monitoring or energy management. Other applications of this design ranges from industries to home usage such as smart plugs, smart appliances, and others that require utility metering.



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