Explain monostable multivibrator and write its application.

Monostable Multivibrator

A monostable multivibrator, also known as a one-shot multivibrator, is a type of electronic circuit that generates a single output pulse when triggered. It has one stable state and one quasi-stable state. Upon receiving an external trigger signal, the circuit transitions from its stable state to its quasi-stable state for a predetermined period of time, after which it returns to its stable state. This behavior is what gives the monostable multivibrator its name: "mono" for one, and "stable" for the single stable state.

Circuit Description

The monostable multivibrator typically consists of an amplifier with positive feedback where one of the resistors has been replaced by a timing element, such as an RC network (Resistor-Capacitor network). The most common implementation uses a 555 timer IC, but it can also be built using transistors, operational amplifiers, or other logic gates.

Operation

The operation of a monostable multivibrator can be broken down into the following steps:

1. Stable State: Initially, the output of the circuit is in its stable state (low or high, depending on the design).
2. Triggering: A triggering pulse is applied to the input of the circuit.
3. Quasi-Stable State: Upon receiving the trigger, the output switches to its quasi-stable state (opposite of the stable state).
4. Timing Interval: The output remains in the quasi-stable state for a duration determined by the timing components (usually the RC network).
5. Return to Stable State: After the timing interval has elapsed, the output automatically returns to its stable state.

Timing Formula

The duration of the output pulse (T) in a monostable multivibrator using an RC network is given by the formula:

[ T = 1.1 \times R \times C ]

Where:

• ( T ) is the pulse width (time the output is in the quasi-stable state).
• ( R ) is the resistance in ohms.
• ( C ) is the capacitance in farads.

Applications

Monostable multivibrators have a wide range of applications, including:

Application	Description
Timers	Used to generate precise time delays.
Pulse Generators	Generates pulses for initializing or triggering other circuits.
Debouncing	Eliminates mechanical switch bounce by providing a clean transition signal.
Frequency Dividers	Divides the frequency of an input signal by producing a pulse for every n number of input cycles.
Missing Pulse Detector	Detects if a pulse in a series of pulses is missing by triggering if the expected pulse does not arrive.
Tachometers	Measures the speed of a rotating object by converting the pulses generated by the object's rotation into a time interval.

Example

Let's consider a monostable multivibrator using a 555 timer IC with the following component values:

• ( R = 10 \text{k}\Omega ) (10,000 ohms)
• ( C = 100 \mu F ) (0.0001 farads)

Using the timing formula, we can calculate the pulse width:

[ T = 1.1 \times R \times C ] [ T = 1.1 \times 10,000 \times 0.0001 ] [ T = 1.1 \times 1 ] [ T = 1.1 \text{ seconds} ]

So, when triggered, this monostable multivibrator will produce a pulse that lasts for 1.1 seconds before returning to its stable state.

In summary, the monostable multivibrator is a versatile circuit used in various applications where a single, time-controlled pulse is required. Its simplicity and reliability make it a popular choice for many electronic designs.