Simple 555 Timer Tester

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The NE555 timer IC is 8 pin DIP which performs a number of tasks in electronic circuitry. It is becoming very much popular among hobbyist as there is a huge list of circuits and experiments which can be performed using it. This project helps to test whether a 555 timer IC is properly functional or not.

This IC testing circuit can test any of the 555 timer IC. This is done by testing whether it is oscillating or not. By using this tester it can be immediately tested whether the timer is functional or not. It also tells if it is shorted or oscillating. If the LED are flashing, the timer is in good working condition and if  the LEDs are OFF or on solid then it is defective. It can also be used as a trouble shooter in 555 based circuits.

In this project the IC is wired in the astable multivibrator mode. When the power is supplied, the LEDs starts flashing which shows IC is in good working condition. Rate of flashing of the ICs can be controlled by increasing or decreasing the value of resistors R1 and R2. 




1-     Resistor

R1 having vlaue10 kΩ , R2 100 KΩ  and R3 equals to 100 Ω


Resistor is an electrical component that reduces the electric current.

The resistor's ability to reduce the current is called resistance and is measured in units of ohms (symbol: Ω).


2-     Electrolytic Capacitor

C1 value 10 uF


Capacitor is an electronic component that stores electric charge. The capacitor is made of 2 close conductors (usually plates) that are separated by a dielectric material. The plates accumulate electric charge when connected to power source.


3-     555 Timer IC

NE555 IC

The 555 timer IC is invented by Mr.Hans camenzind ,it is an integrated circuit (chip) used in a variety of timer, pulse generation, and oscillator applications etc.


4-     LED

20 mA is a Max Current ;Max voltage across  Led is 5volts.


5-     9V DC Battery with connector


6-     PCB


Circuit Diagram

555 timer tester

Figure   Circuit of Astable multivbrator using 555 Timer IC

R1 =10 kΩ

R2=100 KΩ

R3=100 Ω

C1=10 uF


Above figure shows the circuit diagram of a 555 Timer wired in Astable Mode.

·        Pin 4 and Pin 8 are shorted

·        Pin 2 and Pin 6 are shorted

·        A capacitor is connected between Pin 1 and Pin 2

·        R1 connected Between Pin 7 and 8 ; R2 between Pin 6 and 7

·        Led alongwith 100 ohm resistor is connected in series between output pin 3 and Pin 1

·        Power is supplied by 9v dc battery  between pin 8 and pin 1

·        8th pin and 1st pin of the IC are used to give power, Vcc and GND respectively.

·        The 4th pin is RESET pin which is active low and is connected to Vcc to avoid accidental resets.

·        The Trigger (pin 2) and Threshold (pin 6) inputs are connected to the capacitor which determines the output of the timer. Discharge pin (pin 7) is connected to the resistor Rb such that the capacitor can discharge through Rb.




astable multivibrator for 555 timer tester

Figure   internal components and pin configuration in astable mode

  • When the circuit is switched ON, the capacitor (C) voltage will be less than 1/3 Vcc. So the output of the lower comparator will be HIGH and of the upper comparator will be LOW. This SETs the output of the SR Flip-flop.
  • Thus the discharging transistor (Q1) will be OFF and the capacitor C starts charging from Vcc through resistor Ra & Rb.
  • When the capacitor voltage will become greater than 1/3 Vcc ( less than 2/3 Vcc ), the output of both comparators will be LOW and the output of SR Flip-flop will be same as the previous condition. Thus the capacitor continnously to charge.
  • When the capacitor voltage will becomes slightly greater than 2/3 Vcc the output of the higher comparator will be HIGH and of lower comparator will be LOW. This resets the SR Flip-flop. Thus the discharging transistor turns ON and the capacitor starts discharging through resistor Rb.
  • Soon the capacitor voltage will be less than 2/3 Vcc and output of both comparators will be LOW. So the output of the SR Flip-flop will be the previous state.
  • So the discharging of capacitor continuous.
  • When the capacitor voltage will become less than 1/3 Vcc, the output SETs since the output of lower comparator is HIGH and of higher comparator is LOW and the capacitor Starts charging again.  This process continuous and a rectangular wave will be obtained at the output.


Advantage :-

·        A instant check  of 555 timer IC can be done , it reduce the chances of using damaged IC

·        This device is very cheap costing around 25 Rs

·        Small and portable



·        A small amount of maintenance is needed in case of battery being drained .

·        Loose connections of battery ,555 IC and  holder may give false output



Conclusion:-  A damaged IC  destroys all our work and  effort  so Before  working on any 555 timer based project ;it is a good practice to check   IC by  555 Timer Tester ;also it saves a lot of time and keep us away from having a delusion of false ic

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