Here is a simple way to make a Push-On / Push-Off circuit using only a couple momentary switches and a relay. No microcontrollers needed!
What is unique about the circuit, it utilizes momentary switches so you get that “soft touch” feel for start and stop actuation of the function. Basically we are turning a standard non-latching DPDT type relay into a latching function. The relay used is simply chosen based on your circuit specs. The coil voltage chosen will match your power supply input (this circuit will work for either AC or DC circuits by choosing the appropriate relay). The contact rating of the relay will be chosen to handle the current requirements of your load. The switches used can be low current switches, enough to handle the current draw of the coil. A SPDT relay could have been used, but by upgrading to a DPDT type relay we do not route the load current of the device being powered thru the start function switch. Instead it is routed to a dedicated set of second contacts.
