Controlling AC mains using Arduino and removing control easily

Question

I am planning to for an Arduino to read status of a switch, and accordingly switch on and off AC appliance, for a demo purpose. I want to add a feature to it of easy recovery to manual switch control.

^{simulate this circuit – Schematic created using CircuitLab}

First circuit to the left is when Arduino reads status of switch, and controls a bulb by digital pin P2 which drives SSR/relay. Circuit on the right is normal switch board controlled light bulb.

So basically what I am trying is: when I remove Arduino board, my previous control (light bulb controlled only through switch) should be regained. Really stuck on this, help will be highly appreciated :)

Answer 1

I solved it by using a SPDT relay instead of SSR. The N/C contact is attached to the manual switch control. The uC then puts the relay in on state to turn the output off. That way even if uC failed, I could still operate it manually. There are corner cases, of course.

BTW, you might need a DPST or DPDT switch for mains control. One pole directly to relay, the other to uC.

It's kind of relay logic, actually. Think of it as staircase wiring (e.g. http://electricaltechnology.org/2012/11/stair-case-wiring-circuit-diagram-or.html).

Answer 2

Use a two way switch and a two pole relay to act as an two way switch. Normally closed relay with switch in series or switch in parallel but must turned off to give control to the automation.