Commit 78599de6 authored by Sam Calisch's avatar Sam Calisch

Update README.md

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......@@ -7,6 +7,8 @@ This is documentation for an energy monitoring device built around the nRF52832
This device uses the <a href='http://www.ti.com/lit/ds/symlink/drv5053.pdf'>DRV5053VA</a> hall effect sensor to produce around 0.1 volts/amp out of the sensor (or ~1 mV per Watt through the plug). The nrf adc has a +-0.6V reference, 4x gain, and 12-bit conversion, which might resolve 100mW (maybe finer with oversampling). Certainly not precision measurement, but good enough for monitoring appliances.
Actually, in this first design, I forgot that the hall effect sensor has a 1V output baseline (when field is zero). This means in this design can't use the ADC gain in the BC832. To fix this, I should use a sensors near each conductor and measure differentially between them. Not only will this eliminate the 1V measurement offset, but it should double the signal-to-noise ratio.
The nRF52 radio+microcontroller draws 5mA in transmit and receive, so it could operate well within the specs of a coin cell, or harvest from the power line (say, using http://www.linear.com/product/LTC3588-1) to charge a capacitor for power.
Below, we see the flux guides registered into pockets on the pcb.
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