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555 Timer Monostable Multivibrator Circuit |
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Figure 1.
Monostable Multivibrator Circuit Diagram Using the 555 Timer
This circuit
diagram shows how a 555 timer IC is configured to function as a basic
monostable
multivibrator.
A monostable multivibrator
is a timing circuit that changes state once triggered, but returns to
its original state after a certain time delay. It got its name
from the fact that only one of its output states is stable. It is
also known as a 'one-shot'.
In this
circuit, a negative pulse applied at pin 2 triggers an internal
flip-flop that turns off pin 7's discharge transistor, allowing C1 to
charge up through R1. At the same time, the flip-flop brings the output
(pin 3) level to 'high'. When capacitor C1 as charged up to about
2/3 Vcc, the flip-flop is triggered once again, this time making the pin
3 output 'low' and turning on pin 7's discharge transistor, which
discharges C1 to ground. This circuit, in effect, produces a pulse at
pin 3 whose width t is just the product of R1 and C1, i.e., t=R1C1.
The reset
pin, which may be used to reset the timing cycle by pulling it
momentarily low, should be tied to the Vcc if it will not be used.
Learn more about the 555 Timer IC and
its applications...
See
also: Internal Block
Diagram of the 555; How a 555 Operates
Internally;
Op Amp
Monostable Multivibrator;
Flip-flops
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