A Reset-Set flop-flop capable of directly controlling a relay or other power load can be implemented in voltage comparators like the 339 series. In the figure we show the basic circuit where the Set and Reset buttons can be common pressure switches, limit switches, micro-switches, reed-switches or any other type of on-off sensor. Note that this circuit uses two power supplies, with a 24 V load or relay, maximum current of 100 mA. Of course, with the use of Darlington transistors, higher power loads such as motors, solenoids, indicator lamps, etc. can be controlled. The power supply does not have to be symmetrical.
