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Experiment 10 - The Bistable Multivibrator (RS Latch)

Consider the circuit shown. To obtain the functionality of a RS latch with a NE555, the truth table needs to be adapted...

With this you realize a classic RS latch with the NE555.

S1(S) S2(R) Q
open open saved
pushed open 1
open pushed 0
pushed pushed not defined

Truth table of a RS latch with NE555.

Circuit bistable multivibrator circuit (RS latch) with NE555. (Enlarge)

Circuit diagram bistable multivibrator (RS latch) with NE555.

The question remains, why should you use a NE555 as a RS latch? An important argument is the maximum load of the output OUT with 200mA. Comparable logical components (eg C-MOS 4027) can only be loaded with roughly 20mA.

The NE555 as a RS latch is therefore found in control systems (eg, elevator control).

However you are not using the the timer function. This is changing in the next experiment...

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