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Measurement Circuit for Capacitive Sensor

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Sep 15, 2007
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capacitive sensor circuit

I have been struggling with this topic for months and this forum is my last hope.

I have a pressure sensor. This sensor can be modeled as a capacitor. When a pressure is applied to it, it develops a voltage between the upper and the lower electrodes (charges the capacitor). The voltage developed is proportional to the pressure on the capacitor.

With a single sensor, it is not a problem to measure the voltage. Amplifying it with an op-amp and feeding it to the ADC of a microcontroller.

But I need to measure several sensors, connected in matrix mode. The schematics for 2x2 and 3x3 connections are given below.

In this mode of operation I will use multiplexing to measure each sensor capacitor voltage. I will measure the voltages between any two nodes. (I believe one of the nodes has to be the common ground with the microcontroller for ADC conversion).

There is a serious drawback of this connection ( can better be understood by the 2x2 matrix ). When different pressures are applied to each sensor, each capacitor will charge to different voltages.

The question is: due to the different voltages developing on different capacitors, will there be a flow of current that will change the voltages on the capacitors?

How can I measure the voltage developed on each capacitor at the time of the contact?

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