Monday, July 19, 2010

Astable Multivibrator using 555 timer

Ok so I am back. I guess I don't have anything better to do in the world!The Astable multivibrator is stable in two states i.e the low and high and it keeps on oscillating between them with a specific time period determined by the values of resistors and capacitors used. Now we come towards the connections ... Pin  8 is Vcc so it's connected to positive terminal of battery .. here let me tell you that in almost  every IC the last one will be Vcc ... connect pin 1 to negative terminal of the battery and connect your output to pin 3 which can be anything either an LED or speaker.A resistor R1 we'll call it is connected between pin 4 and 7.Another resistor R2 is connected one leg to 7 and other to 2.Pin 6 is connected to 2 and 2 is grounded through capacitor C1.The discharge time is:
td=0.693*(R1+R2)*C1
Charging time is: tc=0.693*R2*C1
Time period is : T=td+tc
Frequency with which LED will flash is: f=1/T so by adjusting the values of resistors and capacitors you can make the circuit resonate at any frequency. The working principle behind this behavior is that when capacitor is being charged the LED flashes but as the capacitor is fully charged it behaves as open circuit and no current flows. A flip-flop which is part of the IC's internal circuitry comes into action and causes the capacitor to discharge through resistor R2 in this way a pulse train of required frequency is generated.
For a demo watch my video on Youtube!




























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