An AVR-based power usage logger

AVR Power Use Meter

Dan wanted to monitor the power usage for his house. He installed some current sensors made from a couple of TV flyback transformer cores. The voltage is stepped down by another circuit. Then both the voltage and current are amplified to the correct levels and the ATmega168 microcontroller computes the power consumped using the formula P=V*I. A graphic LCD shows the power usage and can also display the voltage and current waveforms. All logs are then saved to an SD card. <via MCU Project Everyday>

This entry was posted on Wednesday, October 22nd, 2008 at 9:11 am and is filed under arduino & avr. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.

2 Responses to “An AVR-based power usage logger”

  1. Sparky Says:
    October 23rd, 2008 at 12:16 am

    Nicely done, especially the current transformers, but it has one tiny little mistake: P=V*I does not hold for inductive loads, like refrigerators, and the motor of the washing machine. You need to take the cos(phi) into consideration.

  2. Dan Says:
    September 10th, 2009 at 12:19 am

    Sparky,

    The P=V*I formula does apply for instantaneous power though. When it is integrated over time the phase factor is taken care of automatically. In fact, P=V_rms*I_rms*cos(phi) is just a way to skip doing the integral. The cos(phi) formula is also only valid if all higher harmonics are filtered out.

 

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