Hello,
I need your assistance in a project that I'm trying to do for school. It's a weather station and it involves, among other things, a relative humidity sensor. I have chosen a cheap resistive one for this matter but I can't figure out how to use it
It will have to be read by the ADC from a microcontroller and then the value sent to a computer.
What I’m not certain about:
The datasheet says the resistance is from about 100ohms to 1kohm, rising with the humidity. This is waaay smaller than any other RHS I’ve read about (typically the resistance _decreases_ with humidity from about 4Mohms to hundreds of kohms). I've measured it with a DC ohmmeter (at the time I didn't know about the electrolysis thing... I think it's fried now but I'll get another one) and with a RLC meter @ 1KHz and they both read a couple of Mohms.
Some datasheets (for other RHSs) say that the AC can be a square wave with 0 DC, 1KHz frequency and 50% pulse width (symmetrical). Can I do the same with my sensor? It would really simplify things (I won’t have to build a sine wave generator for that matter).
Reading the voltage can't be very hard, just pass the output through a superdiode rectifier then smooth/convert. It's just not clear how to do that with the schematic from the datasheet: both the RHS and the thermistor for temperature compensation are in the same resistive divider - varying with humidity and temperature. On the other hand I could just bypass the thermistor and use a precision resistor and find out the resistance of the RHS from the output DC since I already have a digital thermometer in the weather station...
Oh well, maybe you can shine some light on this
Hash.
I need your assistance in a project that I'm trying to do for school. It's a weather station and it involves, among other things, a relative humidity sensor. I have chosen a cheap resistive one for this matter but I can't figure out how to use it
What I’m not certain about:
The datasheet says the resistance is from about 100ohms to 1kohm, rising with the humidity. This is waaay smaller than any other RHS I’ve read about (typically the resistance _decreases_ with humidity from about 4Mohms to hundreds of kohms). I've measured it with a DC ohmmeter (at the time I didn't know about the electrolysis thing... I think it's fried now but I'll get another one) and with a RLC meter @ 1KHz and they both read a couple of Mohms.
Some datasheets (for other RHSs) say that the AC can be a square wave with 0 DC, 1KHz frequency and 50% pulse width (symmetrical). Can I do the same with my sensor? It would really simplify things (I won’t have to build a sine wave generator for that matter).
Reading the voltage can't be very hard, just pass the output through a superdiode rectifier then smooth/convert. It's just not clear how to do that with the schematic from the datasheet: both the RHS and the thermistor for temperature compensation are in the same resistive divider - varying with humidity and temperature. On the other hand I could just bypass the thermistor and use a precision resistor and find out the resistance of the RHS from the output DC since I already have a digital thermometer in the weather station...
Oh well, maybe you can shine some light on this
Hash.