Humidity sensor circuit

[Asjad]

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!

 

[canadianpoet2012]

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!

 

[Russlk]

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.