Humidity sensor operation

Thread Starter

skywest

Joined Jul 16, 2014
4
Hi,
I am trying to design a simple system that measure the humidity in my car and switches on a small fan when it reaches a threshold, powered by say a 9v battery, not by the car battery.
So I am trying to research humidity sensors and really can't find out too much about the implementation and operation.
One such is http://www.spiratronics.com/data/8315.pdf but the data sheet doesn't give any info other than electrical characteristics.

Can anyone point me in the right direction please?
 

ericgibbs

Joined Jan 29, 2010
12,199
hi sky,
That sensor needs extra components in order to convert the RH% resistance at a particular temperature to a readable RH value for the user.

Do you have any electronics equipment and knowledge.?
E
 

LesJones

Joined Jan 8, 2017
3,066
I think the simplest method is to use a DHT22 with a small microcontroller. I assume when you say a 9 volt battery you mean a PP3 type. Based on that assumption you would need to only power the electronic for a short time say every minute to conserve the battery. (As humidity will not chance rapidly.) The microcontroller could be programed to be in sleep mode for most of the time.
An alternative sensor is the BME280 which is more accurate but requires more complex software in the microcontroller.

Les.
 

AlbertHall

Joined Jun 4, 2014
11,095
Using a microcontroller is the simplaest if you have the knowlwedge and, possibly, hardware to program one.
If you have never done this before it is far from trivial.
 

wayneh

Joined Sep 9, 2010
17,018
Hi,
I am trying to design a simple system that measure the humidity in my car and switches on a small fan when it reaches a threshold, powered by say a 9v battery, not by the car battery.
So I am trying to research humidity sensors and really can't find out too much about the implementation and operation.
One such is http://www.spiratronics.com/data/8315.pdf but the data sheet doesn't give any info other than electrical characteristics.

Can anyone point me in the right direction please?
If I were trying to do this, I'd pull the sensor and controller from a dead home dehumidifier. These things fail after one season and there are hundreds out there attainable for free. Every part of them works fine but the freon is gone. Get one of the newer ones with the digital readout and digital controls. The old kind use an old-fashioned humidistat sensor. Although now that I think about it, maybe that's exactly what you want. It can accomplish the switching with no electronics or power supply.
 

Thread Starter

skywest

Joined Jul 16, 2014
4
If I were trying to do this, I'd pull the sensor and controller from a dead home dehumidifier. These things fail after one season and there are hundreds out there attainable for free. Every part of them works fine but the freon is gone. Get one of the newer ones with the digital readout and digital controls. The old kind use an old-fashioned humidistat sensor. Although now that I think about it, maybe that's exactly what you want. It can accomplish the switching with no electronics or power supply.
Thanks, good idea, I'll try that.
 

Reloadron

Joined Jan 15, 2015
5,875
For a clean dry environment I would go with Les Jones suggestion using a DHT 22 sensor and as can be seen they are very common and inexpensive. I would use it together with a uC (Micro-Controller) allowing me to easily create a set point. I would pair it with an inexpensive Arduino Uno Clone from Amazon like this one. I would just power the uC board off the automotive 12 volt system and the DHT 22 off the Arduino 5 volts out. If anyone wanted to get fancy just add a LCD.

DHT 22 1.png

Everything modular making for easy interconnect. Including plenty of sample code online.

Just a matter of If RH is greater than .... Do something or whatever one wants to happen.

Ron
 
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