Circuit's Blog :
Return to BlogPower Usage Logger Based on AVR
Posted Feb 07, 2012 at 3:08 pm
Figure 1
The device is used to monitor the power usage of households by logging it into an SD card.
The signals from current and voltage detectors are being amplified by a simple analog frontend while the power consumption is being computed using an ATmega168 microcontroller. A frequency of 9615 Hz is sampled in each current and voltage for accurate integration of highly non-sinusoidal loads like the computers or fluorescent bulbs. The power usage is shown on a graphical LCD as a strip chart which can function as an oscilloscope to display the waveforms of current and voltage. In order to use different gains in giving accurate readings for both high and low power usage, the current is amplified in three stages.
A pair of current transformers, from old TV flyback cores, installed in the fuse box is used to measure the current. Connected to the coil is a current sense resistor where the whole assembly is wrapped in electrical tape for safety. A voltage divider connected to an instrumentation amplifier is used to measure the voltage. It operates on a 5V supply and can accept inputs that allow possible use of Earth ground.
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2 years ago: I guess this is what the guys from electric company are bringing when they check the usage in the meters. They look like collectors with big walkie-talkie :)