humidity sensor

I'm using the HIH-4000 family of sensors ($15-20 at digikey) for my home thermostats. They give out a DC voltage proportional to humidity; if your PIC has an ADC that's all you need. They also interface nicely with the maxim "battery monitor" 1wire chips (such as phanderson uses), which have temperature sensing in them.

You can buy cheaper capacitive sensors for much less, but you need to use them in an oscillator or RC circuit to let the PIC sense the capacitance (and thus humidity). Again, if your PIC has an ADC, you can use an RC circuit between a GPIO output and the ADC to measure the RC constant in software.

example:

Trying to figure out dew point from temperature and humidity can be a thankless task -- the vapor pressure of water varies exponentially with temperature, so anything more than a few degrees difference and you're almost out of luck.

There are dewpoint sensors out there. It may even be fun to build one.

easily? Phanderson

one wire temp

(shop) at

I don't

It will never happen !!

If a Differential thermostat is set to bring in COLD and moist air into a Warm garage, the Tools will always be warmer than the external Air and thus warmer than the Saturated Air . Only if you were to bring in Warm MOIST Air would you get condensation on the COLD Tools.

BY wiring an external Thermostat and Fan to bring COOLER air than the internal Temperature Thermostat; you would never have your tools below the Dewpoint. Besides the fan would cutoff when the ROOM temperature dropped below the ROOM Set Temperature.

Yukio YANO