I am trying to design a circuit to control mains equipment using a microcomputer, probably a Raspberry Pi.
The requirement is:
- The main switch is open (up in the diagram) and (ideally) no current flows.
- When the main switch is closed (down in the diagram), the Pi boots up. The relay R1 must stay open so the load is isolated.
- Later, the relay R1 is closed by the Pi, under software control, so that the load is energised. The load stays on, even if the Pi shuts down.
- When the main switch is opened, the load goes off and the relay R1 is opened, ready for the next iteration.
Is there such a relay type, that would be normally open with no input power, and and then latch closed?
Alternatively, I am thinking of another relay at C1, to open R1 at step 4. Is this a sensible idea?
Please advise on the type of devices for R1 and C1 if appropriate.
I am confident of cabling the mains switch, load and relay. Please note that this not about the Raspberry Pi. There is plenty of information available about using the Pi with relays and relay modules.