> Can anyone recommend a very low cost humidity sensor? A company that
> provides a few free samples is also good.

> I'm working on a project for my university that requires temperature
> and humidity logging, so something cheap, accurate, and easy to use
> would be ideal.

I doubt if this will commend itself in the face of free samples, but:

- Traditional method was to use twisted catgut which changes its
'twistiness' with humidity. This was used to drive a pointer but you
could probably measure force or use it to drive a pot or rotary
capacitor or ...

- I've read that some clothes driers use horse hair ! Whether tis
really so and/or how well it works TBD.

The text at the end is from a UK answers site. This is probably how
the 'real' ones work and if you could establish what the magic
dielectric was you could probably do the same quite easily with a PIC.

Gargoyles ...
Aha
"Nowadays", apparently, "most people prefer ny-l-on instead" "
This 1953 paper suggests that a 15 denier Nylon strand worked very well for them
Page 1 free.
           Note on the Construction of Fiber Hygrometers
           http://trj.sagepub.com/cgi/pdf_extract/24/1/59

Approx 2.8% increase in length across 0-100 RH range.
Accuracy, repeatability, drift etc innown.
Curve shown.
No apparent hysteresis.

__

Lots of subsequent refs. A standard material. Hair better under 10C.




______________

How Analog Humidity Sensors Work
An analog humidity sensor gauges the humidity of the air relatively
using a capacitor-based system. The sensor is made out of a film
usually made of either glass or ceramics. The insulator material which
absorbs the water is made out of a polymer which takes in and releases
water based on the relative humidity of the given area. This changes
the level of charge in the capacitor of the on board electrical
circuit.
How a Digital Humidity Sensor Works
A digital humidity sensor works via two micro sensors that are
calibrated to the relative humidity of the given area. These are then
converted into the digital format via an analog to digital conversion
process which is done by a chip located in the same circuit.

A machine made electrode based system made out of polymer is what
makes up the capacitance for the sensor. This protects the sensor from
user front panel (interface).
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