Nice documentation of what You want to do!
But if my old eyes don't trick me, You mixed up the + and - of the 12 Volt supply to Your "external" valves.
0V must go to - minus of Your Valve coil and the + plus 12V get switched by the relays contacts and than must be connected to the +plus of the valves coil.
(+0V as You write is yes the Zero of the + PLUS 12 Volt supply, but "more" negative then the plus 12 Volt.)
Thanks for reminding me about the polarity. i missed that one out... -ve of the valve should be connected to -ve PS. thanks for that
1 more question, if, let say, i have about 8 solenoid valve 12VDC, 500mA. What type of power supply should i buy?
- 12VDC, 1A? or 12VDC 4A?