July 1998, Issue 96

A PIC-Based AC Power Meter

MY TOP PIC

The PIC software occupies 722 of 1024 words of program memory. I haven’t yet implemented average power measurement or low-battery detection. And, I did the initial calibration using incandescent light bulbs as loads.

The results appear accurate within 10 W, as Woodward’s article indicates. Calibration using the two trim pots was fairly easy. For easier calibration, a multi-turn pot could replace the single-turn trim pot.

Some possible enhancements include use of a higher resolution ADC for more accuracy, removal of pots altogether, larger energy consumption accumulator, and autocalibration.

You just saw how a simple PIC with Microchip’s math routines can be made to do significant computation such as numerical integration. You can use this project as starting point for any instrumentation-type project.

And maybe now I can figure out just what’s making my wattmeter spin so fast.

Rick May is a principal design engineer at Raytheon Systems. He currently designs embedded software for a Navy communications system. You may reach him at rmay@televault.com.