MONOSTABLE MODE OF 555 IC

MONOSTABLE MODE :-

As I promised here is the post on monostable mode of 555 timer IC. In this mode, the 555 timer functions as a “one-shot” pulse generator. The name “monostable” meaning “one stable state”.

APPLICATION :-

Applications include timers, missing pulse detection, bouncefree switches, touch
switches, frequency divider, capacitance measurement, pulse-width modulation
(PWM) and so on. For example monostable 555 circuit is ideal for projects at exhibitions, which needed to work when a visitor pushes the button to start the project’s mechanism moving, and the mechanism will automatically switch off after the time you set.

WORKING OF MONOSTABLE 555 TIMER

In this mode 555 acts as a pulse generator and the pulse starts  when the 555 timer receives a input at the trigger input (pin 2) that falls below a third of the voltage supply.The width of the output pulse is determined by the time constant of an RC network, which consists of a capacitor (C) and a resistor (R). The output pulse ends when the voltage on the capacitor (C)  equals 2/3 of the supply voltage( Vcc). The output pulse width can be lengthened or shortened to your need just by adjusting the values of the capacitor (C) and a resistor (R).

CONNECTION :-

Reset (pin 4) and pin 8 is connected to positive voltage (Vcc).

Discharge pin (pin 7) and threshold (pin 6) pins share a common node (means connected).

Resistor R is connected between the Vcc and the common node that is shared by the discharge pin (pin 7) and threshold (pin 6).

Capacitor C is connected between the common node that is shared by the discharge pin (pin 7) and threshold (pin 6) and GND.

Pin 1 is connected to GND.

A 10n capacitor is connected between control (pin 5) and GND.

Here is all about monostable mode of 555 timer IC. My next post will be on bistable mode of 555 timer IC. If you have any doubts or you like the post, put it in the comment box below.

THE 555 TIMER IC PINOUT

The 555  timer IC is an integrated circuit (chip) used in a variety of timer, pulse generation, and oscillator applications. The 555 can be used to provide time delays, as an oscillator, and as a flip-flop element. The primary purpose of the 555 timer is the generation of accurately timed single pulse or oscillatory pulse waveforms. The 555 has three main operating modes Monostable, Astable, and Bistable. Each mode represents a different type of circuit that has a particular output. I will make a post on the 555 main three operating modes later.

THE FUNCTION OF EACH PINS

Pin 1 Ground [GND] – Most negative supply connected to the device, normally this is common ground (0V).

Pin 2 Trigger [TRIG] – Detects 1/3 of rail voltage to make output HIGH.

Pin 3 Output [OUT] – The 555 timer output signal pin.

Pin 4 Reset [RES] – reset. Must be taken below 0.8v to reset the chip

Pin 5 Control [CON] – A voltage applied to this pin will vary the timing of the RC network

Pin 6 Threshold [THRESH] – Detects 2/3 of rail voltage to make output LOW only if pin 2 is HIGH

Pin 7 Discharge [DIS] – Goes LOW when pin 6 detects 2/3 rail voltage but pin 2 must be HIGH.

Pin 8 VCC [VCC] – Most positive supply connected to device, normally this is 5V, 10V or 15V.

555 IC PINOUT

To identify the Pin1, place the 555 on a flat surface such a way that the small circle is in the top left corner.Now identification of pins are easy. Now start from the top left corner (where the small circle is) first pin is pin1, next pin below is pin2, next pin below is pin3, next pin below is pin4, pin5 is on the bottom right corner, next pin above is pin6, next pin above is pin7, next pin above is pin8.

To identify the pins of IC start from the top left corner where the small circle is and the top first pin will be pin1 and start counting in the pins in anticlockwise direction pin 2, pin 3, pin 4….and stop at the first pin on the top right corner which in the case of 555 is pin 8.

Here I have marked the 8 pins on a 555 iC:-

For the easy understanding of the circuit we always draw the 555 as a building block, as shown below with the pins in the following locations. I have given functions of each pin next to it. So you can remember it easily. I hope you can understand it.

If you have doubt in identify the pins of 555 IC OR function of each pin, put it in the comments and I will help you to solve it.