In SX Microcontrollers, SX/B Compiler and SX-Key Tool, pwillard wrote:

I've been looking for alternatives to the $30 Humidity sensors since I need to scan 6 individual enclosures for humidity and the costs rather skyrocketed for this once-off project.
 

What I've been examining are the Honeywell capacitive sensors that vary from 310-350pF with 0-100% humidity.

 

Reading such a small variance in capacitance seems tricky. The datasheet shows only a test setup with an LCR meter... so that's not giving a good design clue.

 

What comes to mind is a part like a 555 in Astable mode with the Humidity Cpacitance driving the frequency of oscillation.  Converting the frequency to voltage with something like an LM2917 maybe and then reading that voltage at an SX pin with analog in?

 

Ok, that sounds really complicated... but it's all I've come up with in 5 minutes of leaning back in my chair and smoking my pipe.

 

I'm thinking that there must be an easier way.  ideas?

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