What is this device called? A magnetic switch that can turn on and off with a momentary magnetic field?

Question

I don't want a simple reed switch because they will turn off again as soon as the magnet is removed, i need something that will stay on after the magnet has been removed and then turn back off when the magnet is introduced again. does this even exist?

An example of application: having a keyfob with a magnet inside and this device hidden behind the drywall of a house. waving the key fob in the location of the device inside the wall will turn on or turn off whatever the switch is wired to.

any ideas?

Answer 1

A simple flip flop circuit will do that. The flip flop should drive a driver transistor and then a relay. Note that the flip flop's input will need to be debounced to keep the state change stable and definite.

The debouncing circuit should also feed a one-shot circuit. The one shot circuit will give a required pulse, just in case the magnet is held in front of the magnetic switch for a long length of time.



All the above can also be achieved with a mechanical stepping relay, as well.

Answer 2

You could use a latching relay. Basically the relay has 2 coils; one of them drives the relay to a closed state and the other does the opposite. The relay will not change positions if neither coil is energized.

Answer 3

you can use a microcontroller. or use a 555 circuit