How to use Vegetronix soil moisture sensor (VG400) on Arduino

With the summer starting to come to a close it has been time for me to start thinking back to the computerized grow box.  I have been doing some considerable work on the electronics and software over the summer.  Better to break stuff while the plants are outside and not while killing them inside.

Though I have been happy with my homemade gypsum soil sensors I decided to try out a commercial option hoping for better accuracy and longer life.  This is important with my current plans to include automatic watering to the latest version of my grow box.  Don’t want to wake up to a flood in the garage due to a broken sensor.  After some looking I came across the Vegetronix VG400 which measures the dielectric constant of the soil using transmission line techniques.  Which I have no idea what that means but sounds impressive.

The hookup couldn’t be simpler, red wire to 3V, bare wire to ground, and black wire to an analog input.  As you can see below in my completely not to scale diagram below.

From here it all comes down to some simple code to write on the Arduino to get some values.

void setup() {   // Setup serial   Serial.begin(9600); } void loop() {    Serial.println(analogRead(0));       delay(200);  // wait 200 milliseconds }

Upload the code to the Arduino and now I can get a moisture value from the analog input between 0 and 614 (0-3 volts) depending on the degree of water saturation. 

Though not as hacky as my PS2 controller moisture sensor solution definitely more elegant and reliable.  Stay tuned for more details of other improvements to the computer controlled grow box.