INTRODUCTION TO TIMER IC 555 & ITS APPLICATIONS - 4

ANALYZING 
Monostable operation (one shot)
i Change the Resistor Box Values in Monostable Multivibrator

The power supply voltage sat to the 10V DC power and then press the micro switch, LED was ON and after few time it was OFF.

After that, press the micro switch and start the stop watch simultaneously and measured the length of time for which the LED is ON. Recorded this value and repeat the procedure for two times and took the measurements three times. Resistor Value changed. Readings shown below.

So we start stop watch manually simultaneous with micro switch. There will be time delay press both simultaneously, we got average time, because we need minimize error.

According to the Graph 1: Average time value vs. Resistance-C = 47μF, the time increased slightly with respect to the resistance. When increased Resistor box value 1kΩ to 100kΩ LED ON time increased slightly.

Monostable Multivibrators have only ONE stable state and produce a single output pulse when it is triggered externally. Monostable Multivibrators only return back to their first original and stable state after a period of time determined by the time constant of the RC coupled circuit. The time constant of the circuit can calculated using following equation,

 𝑇=1.1 𝑋 𝑅 𝑋 𝐶

We now know that the time delay or output pulse width of a monostable 555 timer is determined by the time constant of the connected RC network. If long time delays according to the equation we can use large value capacitor but problem is it will be physically large and tolerance will be high value. So best thing is we can use large value resistor like 1mega ohm range. According to the above practical we did it. We increased the resistor value and we got results that time delay is increased.

See You with next part.
Laahiru C.Fernando.