Pushing the button once will energize the relay. Pushing it a second time will de-energize the relay. Any simple momentary action push-to-make switch will do. The prototype has a single-pole relay. But you can use a multi-pole relay if it suits your application. The circuit will work at anything from 5 to 15-volts. All you need do is select a relay with a coil voltage that suits your supply.
The LED provides a visual indication that the relay is energized. In effect – it tells you whether the switch is on or off. It’s not necessary to the operation of the circuit. If you wish you may leave out R1 and the LED.
Do not use the “on-board” relay to switch mains voltage. The board’s layout does not offer sufficient isolation between the relay contacts and the low-voltage components. If you want to switch mains voltage – mount a suitably rated relay somewhere safe – Away From The Board.
Copyright Ron J