3

I've had a bit of experience with DHT11/DHT22 sensors in a greenhouse environment, and believe that when they get wet they stop working altogether.

Are there any low cost humidity sensors that I can hook up to an Arduino that don't suffer from this problem, or is there a way to protect these sensors from damage when near water? (I'm not talking about immersing them in water - but do expect condensation to get sprayed with water and/or get condensation on them from time-to-time).

Am I correct that the SHTxx sensors are able to withstand this kind of abuse, and that these sensors are about 5-10 times the cost of DHT sensors? (I did not want to spend that much, but if it's the only possibility I might consider it).

  • use two temps to calc humidity (wet bulb and dry bulb). that would let a pair of cheap but tough thermocouples measure humidity. a neodymium magnet on an analog dial can also be used with a hall-effect sensor. – dandavis Jun 7 '17 at 8:42
  • 1
    Get a proper enclosure for it. – Gerben Jun 7 '17 at 8:50
  • Adafruit has those sinter metal mesh enclosed humidity sensors: adafruit.com/product/1298 There is a big difference between (near) 100% humidity and water condensation or sprayed with water. A capacitive soil moisture sensor can be submersed, but it can not measure the air humidity: wemakethings.net/chirp I suggest to protect humidity sensors with an enclosure as @Gerben wrote (an 'open' enclosure of course) and also use those sinter metal mesh enclosed sensors, and perhaps use a few different types of sensors so hopefully they will not all fail. – Jot Jun 7 '17 at 11:16
  • This HTU21D has a PTFE filter on top of the sensor. Not sure how good they work for water mists. Try checking the data sheet for it. – Gerben Jun 7 '17 at 11:20
  • @dandavis interesting solution Ive not thought of - thank you. Unfortunately I don't think I have the knowledge to pull that off, particularly in my environment with limited airflow (And I don't want to add a fan) – davidgo Jun 7 '17 at 19:29
1

I'd consider using Bosch BME280 digital sensor. Although it's a bit expensive, it has very good sensitivity, precision and amazingly fast response for humidity changes (for ex. in my project it detects dry human hand lying in 2" away within a 1-2 seconds).

So its features make possible to put it into an enclosure to avoid direct water contact with water spays and it'll still be very responsive for greenhouse needs, I suppose. Datasheet warns:

Liquids shall not come into direct contact with the device.

Also, I'd use electronic-friendly protective acrylic lacquer (Plasticote 70 for instance) and put two layers to sensor's PCB, avoiding small black tiny vent hole on the chip itself: BME280

UPD: Here's DHT11 with cover removed: DHT11 inside

It might be the easiest and cheapest solution to cover all internal contacts and IC (avoiding humidity sensor's stripes) of DHT11 with Plasticote 70.

|improve this answer|||||

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.