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What type of photodiode?

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trojsi

New Member
Hi,
I am working on a humidistat project and will be involving photodiodes.
Humidistat are very expensive and rare so I am going to build one for an incubator.

I am going to use a hygrometer (guage ) and use the pointer the cover and uncover 2 photodiodes that will be connected to a mosfet so they will switch a DC fan on and off according to the humidity. (Here the fan will be blowing humid air from a container full of water at about 38 degrees celcius). My question is what type of photo diode do you recommend that will respond on some Bright white LED which will be close to the hygrometer?

Brandon Spiteri
 

Sceadwian

Banned
Humidity | Digi-Key

49 different sensors from 7 makers with at least 3 costing 5-8 dollars. Not exactly rare or expensive.
 
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trojsi

New Member
good idea but...

Hi,
10x for the idea. I really didn't enough or maybe I was putting in the wrong keywords. Would you be so kind and recommend a schematic where I am going to include the humidity sensor or is it the same as I was going to use the photodiode before?

10x

Brandon
 

dougy83

Well-Known Member
most of the cheap sensors exhibit a change in capacitance with the change in humidity. You could probably use a 1kHz squarewave oscillator to drive a capacitor divider (where the sensor is one of the capacitors) and measure the voltage at the junction between the 2 components. I don't think the response is linear, so you may need to compensate for this.
 

KMoffett

Well-Known Member
trojsi,

It looks like you are just looking for ON/OFF switching. Since I don't know what part of the world you're in, I don't know if this will help. I've recovered several humidistat switches from broken room dehumidifiers. Usually the fans or compressors are dead, but the switches are fine.

Ken
 
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