Any chance a thin slice of conductive foam could be used somehow ?

Joe

> Hi, all - need a cheap, cheap, cheap "fog detector" sensor, to tell when
> a piece of glass is getting fogged up.  I've thought of using a
> LED/photodiode pair, which has possibly problems;  Could use an
> enclosed/open thermistor pair, I suppose.  Anyone have ideas?
>
> What I need is a signal "Glass is fogged, or getting slightly fogged" /
> "Glass isn't fogged", it'd be nice if this is $1 or so in price, I want
> to turn a fan on & prevent fogging of the glass, if I can.