555 IC is a timer IC which can be operated in four modes: the astable,monostable,bistable and schmitt trigger(NOT Gate). Right now I'm going to talk about the monostable configuration. The reason it's called monstable is that it's stable in one state which is pretty much obvious and that state is "low", it's "high" state is short lived and dies down quickly.Now let me quickly describe the pins of the IC.Counting starts from the small dot. Pin 1 is ground, pin 2 is trigger, pin 3 is output, pin 4 is reset, pin 5 is control, pin 6 is threshold, pin 7 is discharge and pin 8 is Vcc where you plug in the positive terminal of your power supply. Now to get the circuit running, you connect the pin 1 to negative of power supply. Pin 2 is the trigger so we connect a switch there which is used to trigger the response, the other terminal of switch is connected to +ve of power.Pin 3 is the output where you'll observe the response.You can connect basically anything LED, speaker etc. Pin 4 is the reset. What happens is that when the capacitor gets charged it behaves as an open circuit and no current flows resulting in the stable "low" state. To generate another response,we press the reset button to discharge the capacitor. You connect the pin 5 to a 0.01 microF capacitor which is grounded. This pin is used just to regulate the power. Pin 6 is threshold , the capacitor in use C1 is connected across it and the other leg of capacitor is grounded, pin 6 is also connected to pin 7 and then a resistor R1 is connected to it which then connects to +ve of power supply.Pin 8 is Vcc so we connect it to the power supply or battery or watever you are using!The formula used to calculate the time period is :
T=1.1*R1*C1
The LED will flash momentarily and then it'll go blank until you decide to reset the process with the switch you installed!That's it ... Next up is the Astable Configuration.
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