Below is the Watermark soil moisture sensor plus control electronics. The small plastic freezer bags from the kitchen protected it against the weather:

The Watermark sensor sensor looks like it’s ready for another round of logging. It looks like it’s still in good condition:

Small plastic bags offered protection against the elements:

This is the plastic bag containing the soil temperature sensor, glued onto a aluminum plate. The bag is a bit dirty, but whole:

Amazingly good condition after a year in the ground:

The 1-wire temperature sensor is still in place, glued onto the plate:

The only thing that broke was the plastic cable binder. Strange. It was fixing the two 1-wire Ethernet CAT5 cables on to the aluminum plate:

The next one is the cheap plastic box housing the electronic control circuit for the Watermark sensor. It too has survived without scratches, although the color has changed a bit due to the sun:

The printed circuit board from Hobby-boards is in mint condition! And there’s not even a gasket in the plastic box:

This is the 1-wire air temperature sensor. Also looking good:

Next up is the re-installation of the system in my new garden:

I can’t remember if the Watermark soil moisture sensor should be prepared in some way before being buried in the ground. I have to go read up on that one:

Finally a picture of the newest addition to the system which has not yet been installed:

A rain sensor from Rainwise, that will supplement the soil moisture sensor, to extract even more information about the conditions in the garden.

It pays to watch the soil moisture closely if you want large vegetables. I’ve had good results this year using my garden logging system. Actually my vegetables have gotten a little out of hand. I think the cat is a bit scared too :

I’ve been kind of obsessed with soil moisture now that my logging system is up and running. I’ve checked the log a couple of times a day, and when the moisture level was low I ran out and turned on the sprinkler. I hope the large size doesn’t affect the taste too much.

What I did was that I checked the soil moisture graph and when the level was below 30 % I would water the vegetables. Looking at the graph below it shows that I’ve turned on the sprinkler three times during a week (week 27), Tuesday at 09:00, Wednesday at 23:00 and Friday at 21:00:

This process screams for a computer controlled solution and I’m working on connecting a water pump to the logging system to make it a soil moisture control system instead. It would need a hysteresis, like for instance turning the water ON below 30 % and turning it OFF above 80 %.

Another thing I’m working on is replacing my 1-wire Ethernet cable with proper outdoor Ethernet cable. The existing system has worked without any problems for half a year, but I just want to make the whole system even more durable, since the whole point of building this is to free time and energy and instability problems and break-downs take up just that, time and energy.

(c) 2006 Hobby Boards  Designed by Eric Vickery
Title: Moisture Meter 3
Rev: 3
Date: 10/27/2006 06:11:30p

(Click the picture for a larger version.)

Here’s a bit of explanation on how it works.

The circuit is connected like this:

• Watermark soil moisture sensor: Pin 4 and 5
• 1-wire network: Pin 1 and 2
• 12 volts power supply: Pin 1 and 3

and the circuit works like this:

1. Watermark sensor gets wet
2. The time constant of oscillator IC 555 changes
3. 555 IC oscillates faster and its supply current goes up
4. Current in resistor R2 goes up causing the voltage across R2 to go up too
5. The value of the current register of IC DS2760 changes
6. Current register of IC DS2760 is read via 1-wire network

In my case I got the following values during calibration. I let the Watermark sensor dry in the wind and recorded the current register value, and afterwards the sensor was soaked in a bucket of water:

Dry = -0.2368
Wet = -1.400

These numbers form the 0 and 100 % limits of my soil moisture readings.