How to make a Linux powered garden sprinkler system.

Step 3 Build the Electronics...

The entire process relies on the parallel port from your computer outputing 5v logic to activate the relay and power on the sprinkler vavle.

The Parallel port is capable of provide the 5v logic from the data pins 2-9. This will be +5v when activated and 0v when off. We just need to grab that on off signal and use it to control our sprinkler vavle.

In the diagram  you will see how everything is connected. The 5v logic comes trought the DB25 connector on any pin 2-9 and then powers the coil in the relay and returns to the computers ground. The diode protects the computer from any current stored in the relay coil. when the relay is activated the power from the wall wart will flow through the relay opening the sprinkler valve. thus causing the water to flow.

I used a sharpie to draw a simple circuit to solder the wires for the relay and diode too. Simply draw it on the copper side etch and drill. I also had some screw terminals left over from a previous project that I incorporated but they are not necessary.


 

Comments

[andrew_h]

 I'd really advise against using a parallel port to directly run a relay.  They are not designed to source a lot of current and the port can easily be damaged.  Either use the port to drive transistors to then drive the relay or use something like a ULN2803A which is a darlington transistor array specifically designed for this sort of application.  If the current draw of the solenoid is under 1A you can even drive it from the 2803 directly without a relay.