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The Modern Device Current Sensor at 3.3 Volts

When we designed the current sensor we noticed that the hall effect sensors were rated only for a 5 volt supply in the datasheet, so we didn’t know what kind of performance we would get, if any, with a 3.3 volt supply voltage. So while we were doing the calibration research, we gathered some data at 3.3 volts. We didn’t plug in as many different loads as  with the 5 volt sensor but as you can see from the graph below, the output is very linear, once you get past the very low power “hook” on the left end of the curve, which is due to the “noise floor” from the amplified sensors.


So the good news is that the Current Sensor will work fine on a JeeNode or other 3.3 volt microcontroller. One caveat is that the sensor’s saturation point (maximum reportable value) is also a bit smaller than the 3.3 volts supply,  because the output is governed by the topology of the op-amp peak detector.

Screen shot 2014-05-07 at 3.53.35 PMThe peak detector works with diode D1. The op amp IC1D cannot produce a voltage higher than 3.3 volt supply voltage so the maximum value for the peak detector output at IC1C (pin 8) is going to be 3.3 volts minus the voltage from the diode drop, which in this case is about .2 volts because we used a special schottky diode to try to minimize the diode losses.