This really seems to be a very simple task ..
You can employ any microcontroller (PIC, 8051-derivative, ..) with 12, or more. general purpose Inputs/Outputs and as drivers you can consider BJTs, MOSFETs or integrated drivers such as ULN2003 ( see https://www.xdesignlabs.com/chips/uln2003a.pdf ), that will depend on the current rating of the valves ..
This connection is used to connect the cathodes of the clamping(freewheel/catching) diodes to +V ..
All inductive devices, operating in d.c. circuitry, which are switched on and off (whether by a contact or by electronic circuitry) should have a diode connected across their coils to catch the inductive fly back.
ok now that i understand more about what that diode is for
how do i figure out what value do i use for the diode
how do i calculated the diode value?????
The ULN2003 has the diodes already inside, so you do not need to calculate anything about them. Their ratings match those of the driver transistors, so as long as you do not exceed the transistor current when the solenoid is on, then the diodes will be fine.
imho, there are special types of driver (i dont remember id) which put full voltage at start and after delay reduce it to keep power down and avoid coil heating.
tnp_ngo, put your valve continuously (max time you think it will be laoded) under 12V and check its temperature before proceeding.
To tnp_ngo,
You'd better let us know your valve specs: current, voltage requires, and from which you want to control them: manually, by sensors/transducers, or just PC, ...
More specific info will let us can help you better.
The best way is to buy a sprinkler valve timer with 12 stations. It will run all of the valves and each one is individually programmable for on off times, duration, etc. Cost about $30 US. I use them in my greenhouses and they work perfectly.