In this post we learn a simple IC 555 set/reset application circuit for activating or deactivating a relay alternately.

Simulation and Working

This electronic set reset circuit is very simple, easy to implement and very useful.

It can provide you many applications options in cases where it may be necessary to toggle (switch on and off) any electrical or electronic device

Understanding the ON-OFF or set/reset operation of the timer switch 555

To operate the timer 555. In this popular integrated circuit there a relay is connected via a BJT with the intention of connecting or disconnecting of the device to be controlled.

Manual activation may be performed via two momentary push ON switches. One serves to activate the device under control and the other for deactivating the same.

When the circuit is operating, activation of switch 1 (SW1) enables the pin2 of 555 linked to 12 volts normally, pulling it to 0 volts such that the timer output (pin3) is activated, allowing voltage 12 volts here. Thus, high output activates the relay 555 through the transistor Q1 (which saturates)

For disabling the relay, simply switch 2 (SW2) is pressed.

This puts pin 6 of timer 555, at a high voltage temporarily. The output of 555 that is pin3 now gets a low voltage level at its output, deactivating the transistor in the course, and clearing of the relay.

Circuit Diagram

Note: In the explanation of the circuit, it is proposed to be fed with 12 volts, however it may work well even with a voltage range from 5-15 volts. One can use a 9 volt battery PP3, and thus have a much portable circuit.

IC 555 pinout

IC 555 pinout specifications

List of circuit components for the above explained IC 555 set reset circuit

- Resistors: R1 = R2 = 3.3M, R3 = 10K, R4 = 1K
- Capacitors: C1 = 10nF
- Transistor: BC547
- Rectifier Diode: 1N4148 or equivalent
- Diode LED: 1 red
- Integrated circuit: NE555
- Relay: 1 with identical voltage to the supply voltage of the circuit
- Switches: 2 momentary or similar push ON contact. (SW1, SW2)
- Other: battery connectors (CN3), switches (CN1, CN2). View the latest chart.

By: Manisha Patel

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