2012-06-20

Sensing water

Next step is the sensors for soil moisture of the plants and water level in the tank. I don’t really need very high accuracy in either case, just some indication of the levels.


So I tried a very simple solution. I have been using wireless thermometers from UPM which have very cheap remote sensors sending on the 433MHz band. The actual temperature sensor is some kind of resistive NTC-sensor, and the resistance of the soil will wary with the water content, so I tried a very straight on solution: I cut off the sensor and mounted some random connector I had lying around, (just to get two metal pins with a fixed distance) and stuck that in the soil. And I was lucky – the resistance of the soil with different water content levels matches resistance range of the temperature sensor!


The NetHome-server can read the raw values from the wireless sensor and I get a range from a raw value of 1936 (soil saturated with water) down to 950 (soil dry). So just by cutting a cable I get a wireless soil moisture sensor! I know that you really should use AC current for this kind of measurement and that the resistance may be affected by a lot of other factors, but as ballpark figure this will probably do fine.

5 comments:

  1. Hi,
    I am trying to make soil moisture sensors out of one of my temp/humidity sensors that looks exactly like the one you used but from ClasOhlsson. I have connected wires from the board to nails in the soil. The problem I face is that the readings are HI or LO, I never get into the right resistance window. How do I figure out the resistance to use for the temp circuit and humidity circuit?

    ReplyDelete
  2. Hi. I currently just use the temperature sensor for soil moisture measurement. The "sensors" I use now are thin metal spikes (legs from resistors) that I have put shrinkable tubing (krympslang) around so only about 5 mm of the metal is exposed in the end. I place them about 10 cm apart in the pot, but I adjust the distance so the impedance becomes correct. Hope this helps!

    ReplyDelete
  3. I got it going. I missd a solder point and did not relise recognize that the humidity sensor did not work unless temperature circuit was reading correctly. I also quickly learned that the humidity readings vary with temperature readings..

    ReplyDelete
  4. Tank Level Sensor are commonly used for tank level measurement and control. They offer cost-effective, continuous level measurement and a wide range of features to handle almost any tank level management task. A wide variety of material combinations make them compatible with most liquid media and challenging fluids. Tank Level Sensors are available in multiple sensing technologies including float, radar and ultrasonic liquid level sensing.
    Tank Level Sensor

    ReplyDelete
  5. Are you looking for a level sensor. You will find various types of Liquid level sensor in market, where some of them are cheap and some of them are too costly to buy and also you have to think about price. Icon process Control offering you the best quality Liquid Level Sensor with an affordable price.

    ReplyDelete