555 Bistable

The 555 timer IC can be used with a few simple components to build a bistable circuit, also known as a 'flip-flop'. It is a very simple memory circuit.

The circuit is called a bistable because it is stable in two states: output high and output low.

555 timer IC

Rapid Electronics: NE555 timer (standard)

Rapid Electronics: ICM7555 (low power)

The bistable circuit has two inputs:

Trigger (pin 2) makes the output high. Trigger is 'active low', it functions when < 1/3 Vs.

Reset (pin 4) makes the output low. Reset is 'active low', it resets when < 0.7V.

The power-on reset, power-on trigger and edge-triggering circuits can all be used as described for the 555 monostable circuit.

555 bistable circuit

Bistable operation

555 bistable operation

Projects using 555 bistable:

Rapid Electronics: NE555 timer


Next page: 555 Buffer

Also see: 555 Timer | Monostable