Making Astable Multivibrator using 555 Timer IC

Making Astable Multivibrator using 555 Timer IC

In this article, I will show you how to make astable multi-vibrator with 555 timer IC. It is an 8 pin IC used in producing delays, vibrations, oscillations, etc.

This IC generally works in three different modes that are :

1. Astable Mode

2. Bistable Mode

3. Monostable Mode

It can also be used to make NOT gate. Now here I am using 555 in astable mode as shown in the circuit below.

Fig. 1: Circuit Diagram of 555 IC based Astable Multivibrator

A multivibrator is an electronic circuit which is used to implement simple two-state systems such as oscillators, timers and flip-flops. The name “multivibrator” is because its output waveform is rich in harmonics.

There are three types of multivibrator circuits depending on its circuit operation and harmonics. Here, we are talking about astable multivibrator, whereby the circuit is not stable in either state. It continually switches from one state to the other i.e. low to high and high to low. A video demonstration is shown below with simulation on Proteus.

Note: Proteus is a software for microprocessor simulation, schematic capture, and printed circuit board (PCB) design. The wave generated here is shown in the oscilloscope.

General formulae for using 555 as astable multivibrator are :

1. HIGH TIME =0.69(R1+R2)*C

2.LOW TIME = 0.69(R2)*C

3. DUTY CYCLE = HIGH TIME /(HIGH TIME + LOW TIME)

4.FREQUENCY = 1.44/((R1+2R2)*C)

5.TIME = 1/FREQUENCY