Hobby Boards Moister Meter
The Hobby boards Moisture meter is based on the DS2438.
Tips from Marc MERLIN (valid 2010/05/16)
- Support is limited, you need to read the 'current' value and derive a moisture percentage from there (none is computed for you).
- If you are going to use the soil moisture sensor, the current moisture board has a ground loop that will cause it to show crazy values as soon as you bury the moisture sensor. You must separately buy an isolation transformer (Radio Shack #273-1374).
- You should then measure the current with the sensor fully dry and then fully wet in lukewarm water and use this as your 0% and 100% marks
- Unfortunately, the soil sensor is very temperature dependent when wet (I've seen currents from -1.13 to -1.72 in ice water to hot water). I also recommend wrapping the moisture board in plastic and digging it in the ground a bit to measure soil temperature with the temp sensor on the board. This will let you make a small temperature correction on the current value to derive moisture level (sorry, you're on your own for that table).
- My numbers with the radio shack isolation transformer are: -0.428 when fully dry and -1.72 when fully wet.
- Eric from Hobby Boards said he'd look at adding an isolation transformer to a new design of the board, so check if your has one built in if bought after 2010/05.
Micharel Markstaller notes:
It should work somehow, I have two of them digged, getting something between 0.30 (dry) and 1.29 (wet) in the current field.
BUT: I had many problem getting them to work and still have to reset them every few weeks as they "hang up" somehow!
The order of connecting them seemed to be relevant, connecting GND (both 1w and supply consurrently) at last worked for me..
And there was a big issue when using any two sensors digged with GND and flapping values, I had to add an isolation-transformer between board and gypsum-sensor, see here:
You should calibrate them yourself *after* adding the transformer (if needed)..