A negative pulse applied to the input of the circuit shown in figure bellow turns on the relay. The next pulse will turn off the relay. The bistable action of the block is obtained thanks the use of one of the two flip-flops of a 4013. The relay can be any type depending on the power-supply voltage and a current up to 50 mA. In this example the inputs of the unused flip-flop are grounded. The pinout of the 4013 can use the other flip-flop of the 4013 for other applications, including a second bistable.
