Humidity sensor circuit

Dear Folks,

I am trying to interface a PIC to a

Philips -> humidity sensor (capacitive varying).

From the datasheet it says

10% RH = 112pF
90% RH = 142pF

What kind of circuit could detect such samll changes???

The datasheet suggests this circuit BELOW




WHERE IS THE OUTPUT TO THE PIC??

Any easier circuits???


Thanx!

Asjad,

There are two outputs on this circuit! The top half uses two D-type flip flops. The second one (FF2) is the one that contains the outputs. On the right of it are two connectors, Q and NOT Q, (Q with a bar above it). The one that you need to connect to your PIC is the Q output.
All the NOT Q output does, is give you an inverse of the Q output. So, say there was +5v on Q, there would be -5v on NOT Q.

As for the bottom half of the circuit. That is just an oscillator circuit. Which provides FF2 with a clock pulse.

I would use this circuit, if it was on the datasheet then it will have all the right characteristics and ratings for your PIC in that particular circuit. So good luck!

There is an error in the circuit: The connection between FF1 Q and the 30K resistor, 20K pot should not be there. Otherwise, once q goes low the circuit will hang.