Astable Multi-vibrator using 555 Timer
Construction
>> Pin 4 and Pin 8 are short circuited ; Because Pin 4 is Active low pin and if it is leaved free and it will reset the flip flop , so to avoid such condition the pin 4 is connected to a ‘high’ state
>> Pin 2 and 6 are short circuited; By doing this we tied together upper comparator and lower comparator pins (upper comparator Non inverting and lower comparator Inverting.
>> The Resistor RA is connected Between Pin 4 and Pin 7.
>> The Resistor RB is connected Between Pin 6 and Pin 7.
>> The power supply is connected between Pin 1 and Pin 8 ( 9V ) , Positive terminal is connected to pin 8 and negative terminal is connected to pin 1.
>> The output is generated at pin 3 , a LED is connected between Pin 3 and Pin 8 , aternatively can be connected between Pin 3 and Pin 1.
>> The frequency LED blinking is given by the formula .
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| 555 Timer | LED |
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| Dc Battery | Printed Circuit Board |
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| Capacitor | Resistor |
Internal structure of 555 Timer.
SR Flip Flop
In electronics, a flip-flop or latch is a circuit that has two stable states and can be used to store state information. A flip-flop is a bistable multivibrator. The circuit can be made to change state by signals applied to one or more control inputs and will have one or two outputs. It is the basic storage element in sequential logic. Flip-flops and latches are a fundamental building block of digital electronics systems used in computers, communications, and many other types of systems.
The design of such a flip flop includes two inputs, called the SET [S] and RESET [R]. There are also two outputs, Q and Q’. The diagram and truth table is shown below.
S=1, R=0—Q=1, Q’=0
This state is also called the SET state.
S=0, R=1—Q=0, Q’=1
This state is known as the RESET state.
S=0, R=0—Q & Q’ = Remember
If both the values of S and R are switched to 0, then the circuit remembers the value of S and R in their previous state.
S=1, R=1—Q=0, Q’=0 [Invalid]
This is an invalid state because the values of both Q and Q’ are 0. They are supposed to be compliments of each other. Normally, this state must be avoided.
Comparator
In electronics, a comparator is a device that
compares two voltages or currents and outputs a digital signal indicating which
is larger. It has two analog input terminals
and
and
one binary digital output
.
The output is ideally
NOT Gate (inverter)
The output of NOT gate is the complement of the input.
Detail Explanation of Astable Multi-vibrator 555 Timer Circuit .