On Mon, 28 Feb 2011 13:07 -0800, "alan smith" wrote:
> I have a sensor, that when its activated, it goes from a 15ohm to open
> circuit.  This is a battery powered device, so low current is critical.
> It will bounce back and forth, as its a motion detector of sorts.=20
>=20
> The approach I was going to take (and build up to test later) is to put a
> 330K resistor in series being fed by the box 3.3V power, and connect the
> A/D of the PIC between the sensor and the resistor.  Normally it will
> pull some small amount of current and thus a voltage drop to measure, and
> on a open circuit if course it should read zero.
>=20
> Any other ideas on measuring for an open circuit with very low power
> consumption?

Hopefully you have an extra pin to use.

If the sensor is normally low resistance then I would use an output pin
to energize your 330K resistor and only switch it on for a few
microseconds right before polling the sensor, then turn it off. No need
to use an A/D unless your sensor has a variable output.

Cheers,

Bob

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