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[on:]

How could one make a humidity sensor?

Preferably with scrap lying around the house. Or do you know any electronics that contain humidity sensors?

[Reply #1 on:]

Human hair!!!
Do they count as scrap???

[Reply #2 on:]

It depends on what you want it for

Perhaps this: http://www.cheapvegetablegardener.com/2009/03/how-to-make-cheap-soil-moisture-sensor.html

[Reply #3 on:]

I think most relative humidity sensors are some kind of capacitive sensors wich use the fact that humid air conducts more.
so you make small open air capacitive sensor with a small gap and mesure the capacitance using cap sense library
Test with 100% humid air (over boiling water for example or in the bathroom shower right after running it).
test 0% with placing it in a closed jar with silica gel packs (used with electronics to keep it dry, the do not eat small packages)

David

[Reply #4 on:]

I was just thinking along the same lines.

Correct me if I'm wrong:
I would use copper to make it because it has a high conductivity or silver if i had some.
The gap would be 1/10th centimeters apart? Or could i afford to have larger gaps.

I'm not so sure if it's as simple as connecting arduino analog pin 1 to the prototype sensor to ground.

[Reply #5 on:]

wich use the fact that humid air conducts more

No that is not how a humidity sensor works, it is a dielectric effect.

http://www.sensorland.com/HowPage047.html
Says:-

Conventional sensors determine relative air humidity using
capacitive measurement technology. For this principle, the
sensor element is built out of a film capacitor on different
substrates (glass, ceramic, etc.). The dielectric is a polymer
which absorbs or releases water proportional to the relative
environmental humidity, and thus changes the capacitance
of the capacitor, which is measured by an onboard electronic
circuit.

Using human hair can work, put it under tension and twist it. With a change in humidity it will untwist. A double strand can trap a thin piece of card or plastic in it and act as a pointer. You can measure the movement of this pointer with optics.

[Reply #6 on:]

Scratch that, I'm not making a humidity sensor anytime soon. Fiber optics, precision assembling... don't think Its worth it. I'll just buy one next time i go to my local electronics store. :

[Reply #7 on:]

I've been known to scavenge some temp/humidity sensors from thermostats.  I have some Sensirion SHT-11s.  They're pretty good sensors.  I think I have one mounted to a board that you could use on your arduino.  I have code also.