Jerry, I designed a PIC-based weather station a few years ago. There are
several options to measure humidity. You have to make a decision based on
environment, accuracy, cost, and ease of use. There is no simple answer
without knowing more about your project.

   Low-cost humidity sensors behave like capacitors that vary with
humidity to change the frequency of an external oscillator. Typical relative
humidity ranges from 10 - 90%. Philips makes (or use to) a low-cost sensor
(P/N 2322 691 90001). General Eastern also have low-cost sensors in their
G-CAP line. Their sensors cover 1 - 100% RH.

   For my project, I needed better accuracy and I wanted to reduce the
complexity of the support circuitry. I ended up using HyCal sensors which
provide an output within 0 - 5V and require minimal support. The outdoor
sensor is an IH-3602L which comes in a T0-39 can with a slotted cap and for
the indoor sensor, I used the IH-3605 hybrid element. Both sensors operate
from 1 - 100% and provide an output from around 0.8V - 3.9V with a 5V
supply. They should be buffered and require a simple low-pass filter and, as
with most sensors of this type, need to be shielded from sources of bright
light. You do need to factor in temperature compensation so you need to
measure ambient temperature near the sensor. You normally combine both in a
package for your outdoor sensors.

   There are more sophisticated sensors that provide a voltage, current, or
pulse output and include the temperature sensor giving humidity and/or dew
point. For more info contact:

      HyCal: http://www.honeywell.com/sensing/prodinfo/humiditymoisture
      General Eastern: http://www.geinet.com/
      Philips        : (817) 325-7871 (Note, may be discontinued...)
      Omega:         : http://www.omega.com

   - Tom

At 05:57 PM 9/22/99 -0400, Jerry Iacobucci wrote:
>Thanks in advance for any info
>
>Has anyone come across a company that produces a device (sensor) that will
>measure relative humidity, or know of a device. I need to interface to a
>pic.
>
>Thanks
>
>Jerry Iacobucci


------------------------------------------------------------------------
Tom Handley
New Age Communications
Since '75 before "New Age" and no one around here is waiting for UFOs ;-)