On And Off Button


In this simple circuit
we give the chip a little more attention than usual. It is astonishing
what can be built with a 555. We are always infatuated with simple
circuits using this IC, such as the one shown here. The 555 is used here
so that a single push-button can operate a relay. If you press the
button once, the relay is energized. When you press it again the relay
turns off. In addition, it is possible to define the initial state of
the relay when the power supply is switched on. The design is, as
previously mentioned, very simple. Using R1 and R2, the threshold and
trigger inputs are held at half the power supply voltage.

Circuit diagram:

On/Off Button Circuit

On/Off Button Circuit Diagram

When the voltage at the threshold pin becomes greater that 2/3 of
the power supply voltage, the output will go low. The output goes high
when the voltage at the trigger input is less than 1/3 of the power
supply voltage. Because C2, via R3, will eventually have the same level
as the output, the output will toggle whenever the push-button is
pressed. If, for example, the output is low, the level of the trigger
input will also become low and the output will go high! C1 defines the
initial state of the relay when the power is applied. If the free end of
C1 is connected to Vcc, then the output is high after power up; the
output is low when C1 is connected to ground.

Author: Ger Langezaal – Copyright: Elektor Electronics


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