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what's the difference between monostable and a stable

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nutty boy

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May 7, 2005
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Can someone pls tell me what's the difference between monostable mode and astable mode in 555 timer circuits

Monostable will generate only one pulse; astable will generate a square wave.
In other words, monostable=one-shot, astable=free-running.
And 555 (indicated by Rectifier) is a very good example of both modes.
yes, what IanP said is quite right.

I'm very familar with 555 timer, it's

a great little IC, it has been invented for

about forty years. it has many use.

the monostable and astable are

two operating mode of a 555 timer.

and a 555 timer can be use as a RS latch.

now, talk about your question.

1) monostable : mean that the circuit has

a stable state. for 555 timer,

this state is low output state.

when a 555 timer use as a one-shot,

after a signal triggered the circuit,

the circuit will output a high level

pulse, then go back to low output state.

the pulse's width is determined by external

RC parameter.

2) astable: when a 555 timer use as a oscillator,

its output will swicthing between high state and

low state periodically, THE CIRCUIT DO NOT EXIST

A STABLE STATE if begin operate.

3) RS latch: when a 555 timer is used as a RS latch,

as we know, it will has two stable state,

high state and low state.

oh, perhaps it will exist a metastable state

in some special cases. but that beyond our


best regards

nutty boy said:
Can someone pls tell me what's the difference between monostable mode and astable mode in 555 timer circuits
monostable produces pulses when triggered. while astable doesnt need input trigger, it continuously generates pulses
I think that Jeffttan says true. A monostable multivibrator needs a trigger signal to produce an output pulse, but an astable multivibrator runs and needn't to be triggered for every output pulse. We can say that an astable multivibrator is an oscillator.
monostable means which has one stable state.and bistable means two stable state,and another one is astable which has no stable state,these r three types of operation.astable mode is for oscillator.
with the monostable you can use just one position. high level or low level. if you have low level you can use high level for once accordind to your input signal. you can vary the time for the high level by using a rc circuit. time is proportional with "r*c".
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