555 clock circuit

555 clock circuit

555 is an IC used to generate a clock .The two attributes of a clock are

  • Frequency
  • Duty cycle.

Pin Configuration of 555

Pin Configuration of 555

Both of these can be changed using this IC, however the duty cycle is always <50%. There are two modes in which 555 can run.

 

Monostable mode

 

As the name suggests; in this mode the output is stable in only one (mono) state i.e. ‘off’ state. Thus it can stay only for a finite time, if triggered, to the other state i.e. ‘on’ state. This time can be set choosing appropriate values of resistances in the formula:

T = 1.1 x R1 x C1

 555 in monostable mode

555 in monostable mode

A stable mode

In this mode; the output is stable neither in ‘high’ state nor in ‘low’ state. Hence it oscillates from one state to another giving us a square wave or clock. We can set the clock frequency and Duty cycle D by the formula:

555 in astable mode

555 in astable mode

 

 

NOTE: Capacitor C2 is just to filter the noise and its value can be suitably chosen to be 0.01μF. It can also be neglected.