Gardena T1030 Water Timer
As I live in a rented flat, which already has an automated watering system in place I wanted to make use of the existing system, but add a little bit more finesse to the control and have it more fully integrated into my existing home automation stuff.
There Gardena T1030 has a standard RCA style plug which links it's 9v power supply and control system, to the sealed solenoid valve which controls the water supply - it looks, therefore, like it should be trivial to hack.
Opening and Closing the Valve
It would seem logical that the valve will open and close just by feeding it 9v or not, but this isn't the case. Some initial research shows the controller doesn't give 9v, in fact, my DMM didn't show much of any reading despite trying the various positions on the control dial.
Some Googling brought back this page; http://www.elektor-labs.com/project/water-management-gardena-t1030130495-i.13273.html
This seems to be suggesting a negative pulse of 9v, at 50ms to open the valve and a positive pulse of 10ms width, to close the valve. I'm not entirely clear on whether the voltage should be 9v at this point, but that's my working assumption.
Because we need a negative and positive pulse, I'm going to have to use a h-bridge, I think. Probably a L293NE.