Are you feeling tired of paying large electric bills? Probably you feel that some tweaking in home electric system would save couple bucks. So why not to try, but for this you will probably need a power level monitor to determine where are biggest usage of electric. Building power level monitor can be quite easy – there can any microcontroller be used for this. In this case a LPC2138 ARM7 microcontroller has been chosen which, I think, probably is too powerful for such simple task.
The simple idea of design is to sense current and step down voltage to level acceptable to MCU IO ports. The current sensor is made of transformer with some modifications. Device detects zero crossings of voltage and current in order to determine the phase shifts so it could calculate power RMS correctly. Power level information can be viewed in two ways – via 7 segment LED indicator mounted directly on device or it can be sent via USART to monitor it computer screen and probably so some statistics. The full project can be downloaded here.