For making this circuit you will need basic knowledge of electronics, also you need to know how to make a PCB. If you don't know how to make a PCB and you want to know how, we recommend you to go to google and you tube and search "How to make a pcb" before you continue with this tutorial.

What we need?
The material we need to make this circuit its really little. I found all the material really easy. You will need:

nand shmith IC (I use 74S132)
a npn transistor
3- 1K resistor
1- 1.2 M resistor
1- 10 K resistor
1- potenciometro 50K
two leds
one switch
one electrolitic capacitor 10uF 100V
one diode 1n4007 or similar
4 header terminals with two screws
one relay of 12v
a copper plaque of 7X7 CM

If you like this please visity my blog: http://bioespin.com/

Step 1: Schematic

What this circuit makes is measure the resistance of earth between the probes. IF the earth is wet the resistance of the soil get smaller, that makes that the circuit became close and the water pump goes off. The circuit its really efficient so you can use it with batteries and they will last a really long time.

This is the schematic circuit:

Step 2: The Circuit

if you want the pcb files to print please go to my web site: www.bioespin.com

there you will find the pcb ready to print and transfer directly to you copper board. The circuit looks like this:

Step 3: Setting Up

The circuit connects like this:

1. Connect the probes
The probes are only two wires that goes to the ground. For better use you can attach two nails in the end of the cable, and when the nails get rusty you just have to chance the nails and not the full cables.

2. Connect the water pump.
Cut carefully the cable of the water pump, the place the two ends in the header blocks named pump in and pump out. It doesn't matter what cable you use like in and what cable you use like out, but you have to make sure to place the right end with the right end. *Caution, all the connections have to be made with the current unplug. Electricity is dangerous and can kill you. Take care of your life.

3. Connect the voltage source
If you use batteries or a wallet connection, be sure you get the Voltage in the right polarity.

We recommend strongly to use a solar water pump. The initial cost is higher, but in the end you don't waste batteries or energy from your house. Also you help the planet. If you don't know the solar water pumps here is an image.

Get the probes in ground separate by 2 or 3 cm. Connect the voltage source to the circuit and you are ready to go.

Step 4: Thanks

If you like this project please visit my website. We are two mexican students of mechatronics engineering and we are working in developing a site with instructions on how to make green technology devices that helps reducing the impact of men on the planet.

Blog: http://bioespin.com/

I hope you like the site, and please fell free to comment :)