# 555 Timer Circuits or Projects Ideas for Engineers

555 timer is an important device in embedded system design which is frequently used in several electrical and electronics projects for generating clock pulses. The 555 timer circuit is produces precise clock pulses which can be used to control the applications as over requirement. Even though the majority of people don’t have any information about the internal circuitry, so, here I want to explain the working of this 555 circuit such that you can build many projects around it and implement your experiments.

## 555 Timer Circuits

The 555 timer integrated circuits are used to generate an  accurate square wave commonly used in many electronics circuits. The 555 timer circuit has designed with 20 transistors, 16 resistors, 2 diodes and a flip-flap. It can be operated in the range of 4.5v to 15v DC supply. The 555 timer IC has basically three functional parts such as;

#### Comparator

It is used to compare two input voltage levels which is inverting (-) one and non-inverting (+) terminals. If the voltage is high at the non-inverting terminal, then the output is high. The input resistance of ideal comparator is infinite.

#### Voltage divider

As the input resistance is infinite in the comparator, so the voltage among all the three resistors is equally divided and this value across each resistor is Vin/3.

#### Flip/Flop

Flip/flops are digital electronic devices having memory. If the input is high while low at R, then the output at Q is high. And when S is high, Q output is high and if R is high, Q output is low.

## The 555 Timer Electronics Circuits in Different Operating Modes

#### Monostable Mode

In monostable mode, the 555 timer IC generates only single pulse when the timer receives a signal from trigger input button. Duration of pulse depends upon the values of the resistor and capacitor. If a triggering pulse is applied to the input through a push button, then the capacitor is charged and the timer develops a high pulse and then it remains high until capacitor completely discharges. If it is required to increase the time delay, then higher rate of resistor and capacitor are needed.

#### Astable Mode

In this mode, the 555 timer circuit generates the continuous pulses with specific frequency depends on the value of the two capacitors and resistors. Here the capacitors charges and discharges from a specific voltage.

If the voltage is applied to the circuit, then capacitors get charges continuously through resistors then 555 timer circuit produce continuous pulses. In this circuit pin 2 and 6 are shorted together for continuously re-trigger the circuit. If the output trigger pulse is high, then capacitor completely discharges. Long time delay achieved by using the higher value of the capacitor and resistors.

#### Bistable Mode or Schmitt Trigger

In this mode, the 555 timer circuit produces two stable states signals which are high and low states. The output signals of high and low state signals are controlled by reset and trigger the inputs pins, not by the charging and discharging of capacitors. If a low logic signal is given to the trigger pin, then the output of the circuit goes to the high state. If the low logic signal is given to the reset pin, then the output of the circuit goes to the low sate.

## 555 Timer Circuit Projects for Final Engineering Students

The 555 timer is a square wave multi-vibrator which is used in many electronics mini projects  to generate the pulses which is used to perform the required operations. Here provided some advanced 555 timer projects for engineering students which are very useful.

### Low Voltage Dc to Higher Voltage DC Using 555 Timer

The main concept of this project is to develop the voltage approximately twice to the input voltage using the voltage multiplier principle. If the input voltage is given around 6 volts DC, then we achieve the output around 10 volts DC. This project uses a 555 timer circuit operating in astable mode that delivers the clock pulses to charge the capacitors that are arranged in series. Then this charged capacitors develop the voltage that is approximately equal to the twice the input voltage. The output can be measured by the multimeter.

### Operation Jamming Device For TV

This project is used to block the emerging signals from the TV remote by generating pulses from the IR sensor connected to this circuit. This project is designed with 555 timer circuit that is operated in astable mode which generates high-power pulses which are given to the IR sensor. The IR sensor produces the IR rays in the range of 38 KHz as a result of pressing any number on it. These rays prevent the IR rays coming out from the TV remote.

### Wire Loop Breaking Alarm Signal for burglars

This project is designed with a 555 timer which is used to detect any thief attempt to breaks the window glass act to give an alert audio signal with use of a buzzer. It is amazing technology for security systems. If the wire of the loop breaks, then the 555 timer circuit is operated in astable mode which triggers the buzzer to give a sound for indication.

### Hidden Active Cell Phone Detector

This system is used to detect the any activated mobile phone from a distance of about one-and-a-half feet to avoid the use of un-authorized cell phone in defense security and probated areas.

The active cellphone detector is designed with 555 timer circuit operated in monostable mode. if any one tries to make a call or send a message then the buzzer will give an indication presence of an active cell phone.

The concept of this project is to control a load for short-time duration by using a 555 timer and a touch-sensitive switch. This is an IC 555  projects operated in monostable mode which is triggered by a touch plate connected to its trigger pin. The output of the 555 delivers logic high for a fixed time interval as decided by the RC time constant. This output drives a relay to switches on the load for that duration after which it switches off automatically.