Generating time delay using astable mode of 555 timer IC

This circuit based project demonstrates the working of 555 timer in astable mode to generate pulses of time period 0.5 second. This pulse can be further used for anything where we need a pulse such as to blink a LED or to create fashionable blinking lights. Image below shows internal circuitry of NE 555 timer which can be used in astable and monostable mode:

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Fig. 1: Prototype for Internal circuitry of NE 555 timer Circuit on Breadboard

This circuit of this project makes the use of timer IC NE555 which produces a constant square pulse of a desired frequency. This pulse could be either triggered or could be produced continuously depending upon the mode of 555 we are using. The two mostly used modes of 555 are Monostable and Astable. Here it is used in the astable mode with time period of half second, with high time period of 0.333 seconds and low time period of 0.166 seconds.

For astable mode total time period is [ln2C*(R1+2*R2)] with high time period as [ln2(R1+R2)*C] and low time period as [ln2(R2*C)]. Here R1 is the resistor connected between VCC and pin7 (discharge pin), R2 is between pin7 and pin2 (trigger pin) and C1 is the capacitor connected from pin2 to ground. For 555 to function in astable mode pin2 and pin6 (threshold) pin must be shorted. Reset pin is connected to VCC.

The output of 555 is taken at pin3 which is in the form of square wave and is then fed to lighting circuit which glows when output is high and stops when it becomes low; there by producing pattern of blinking lights. By varying the value of R1, R2 and C1 square waves of different time periods can be obtained.