555 Timers : Simulation on Proteus

The 555 timer is an integrated circuit (IC)  that can generate timing signals and pulses , which are used in a lot of micro-electronic applications.



                   

The 555 timer has three modes of operation :
1. Bi-stable
2. Mono-stable
3. Astable

Bi-stable Mode or Schmitt Trigger Mode

In bi-stable mode , the 555 timer acts as basic flip flop.

The Trigger and Reset pin are held at 5V. While the THR(threshold pin) is grounded.  On grounding the Trigger Pin the flip flop is set.

Mono-Stable Mode

In mono-stable operation , the output pulse ends when the voltage on the capacitor equals 2/3 of the supply voltage.Thus the output pulse can be varied by changing the value of the capacitor.

Astable Operation Mode

In a-stable mode the timer is configured to generate a series of pulses at a specified frequency. This frequency can be set by changing the value of R1, R2 or C.

Make the following circuit on Proteus to simulate the timer in -stable operation .The 

LEDs will flash alternatively. On decreasing the value of the capacitor , you will notice that a delay is introduced between flashes.