555 Timer Astable Multivibrator Circuit

This 555 Timer Astable Multivibrator Circuit is simple and easy.

Astable means output never stays stable.

Output keeps switching high and low again and again.

Circuit creates square wave pulses.

It is used for LED blinking, tone generation, clock signal and many hobby projects.

Circuit Working:

Parts List:

When circuit starts the capacitor at pin 2 and pin 6 is empty.

Voltage is low.

555 output at pin 3 goes high.

Capacitor begins charging through resistor R1 and resistor R2.

As capacitor voltage rises, it reaches 2 by 3 of supply voltage.

At this point 555 changes state.

Output at pin 3 goes low.

Now pin 7 starts working.

Pin 7 does not connect to ground in wiring.

Inside the IC, pin 7 is pulled to ground by internal transistor.

Because of this the capacitor discharges only through resistor R2 into pin 7.

Capacitor voltage drops.

When capacitor voltage falls to 1 by 3 of supply then 555 changes state again.

Output at pin 3 goes high.

Internal transistor turns OFF.

Pin 7 becomes open again and stops grounding.

Capacitor starts charging again through R1 and R2.

This charging and discharging keeps repeating.

So output becomes square wave continuously.

Formulas:

Formula for 555 Astable Multivibrator

Time high:

Th = 0.693 × (R1 + R2) × C

Using R1 = 1k, R2 = 100k, C = 1uF

Th = about 0.07 seconds

Time low:

Tl = 0.693 × R2 × C

Using R2 = 100k, C = 1uF

Tl = about 0.069 seconds

Total time:

T = Th + Tl

T = about 0.139 seconds

Frequency:

F = 1 ÷ T

F = about 7.19 Hz

How to Build:

To build a 555 Timer Astable Multivibrator Circuit following are the steps to follow:

• Take all the parts as shown in circuit diagram.
• Pin 1 goes to ground
• Pin 2 is connected to capacitor C1 positive and negative to GND
• Pin 2 joined with pin 6
• Pin 3 is output and is connected GND
• Pin 4 goes to VCC
• Pin 5 goes to ground through 10nF capacitor C2
• Pin 6 joined to pin 2
• Pin 7 to junction of resistors R1 and R2
• Pin 8 goes to VCC

Conclusion:

555 Timer Astable Multivibrator Circuit is very a simple project to try for.

Only few parts needed.

Output is stable and repeatable.

Useful for many timing and blinking applications.

Formula is easy and predictable.

Good for beginners and hobby users.

References:

Multivibrator