555 Timer IC Tester

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 both the LEDs are flashing, the timer is in good working condition and if both 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.

When the voltage is supplied to pin2 (trigger input), it is less than 1/3 of supply voltage. The output of the lower comparator forces the flip flop to have low logic state which means output stage has reversing action. In other words, we can say that when the output of the flip flop is LOW, the 555 timer’s output goes HIGH.

When the power supply is first connected to astable circuit then initially the timing capacitor C1 is discharged. The voltage at pin2 becomes 0V and the output of timer is driven HIGH. Capacitor C1 starts charging through R1 and R2. C1 is also connected to pin6 which is threshold input of the timer. As the voltage across C1 increases above 2/3 value of the supply voltage the internal flip flop toggles. The pin7 becomes low which makes C1 to start discharge. As soon as the voltage across C1 goes below 1/3 of the supply voltage the internal flip flop resets and pin7 becomes high. Again c1 starts charging and the process goes on. This is possible only if the IC is in good working condition. The flashing of the LEDs depends on the charging and discharging frequencies.