HOW TO MAKE A CONTINUITY TESTER CIRCUIT USING 555 TIMER

Continuity Tester is a simple electronics tool that indicates continuity of a circuit when that circuit is connected between the connecting probes of Continuity Tester Circuit. This Continuity Tester circuit can be easily made by using a simple 555 timer.

 

IC 555 timer is one of the most popular IC  among electronic hobbyist and engineers, even after more than 46 years of its invention.

Due to its wide range application in electronics, many projects can be easily made using this IC. 555 timer is used for many purposes in electronic industry as a monostable and astable multivibrator. 555 timer can also be used as a CONTINUITY TESTER in its monostable mode or single shot mode.

 

 

COMPONENTS REQUIRED:
Components required for this project:
1.555 timer Ic
2. one buzzer
3.capacitors 100uf and .01uf
4.9volt battery
5. resistors 4.7k and 47k
6.connecting probes

 

CIRCUIT DIAGRAM:

 

Continuity Tester Using 555 Timer

 

 

 

 

 

 

 

*C.P = Connecting Probe

PIN NO. CONNECTION
1 GND  To -ve terminal of battery
2 TRIGGER  Between one C.P and 4.7k resistor
3 OUTPUT  To Buzzer
4 RESET  To +ve terminal of battery
5 CONTROL  To .1uf capacitor
6 THRESHOLD  Between 47 k resistor & 10 uf capacitor
7 DISCHARGE  Between 47 k resistor & 10 uf capacitor
8 VCC  To +ve terminal of battery

 

 

COMPONENT  CONNECTION
4.7k  Between 8 pin and 2 pin
C.P A  To 2 pin
.1UF cap.  Between 5 pin and 1 pin
100 uf cap.  Between 6 pin and 1 pin
47k res.  Between 7 pin and 8 pin
Buzzer  Between 3 pin and 1 pin
C.P B  To 1 pin

 

 

Want to know how 555 timer works?

Check out this awesome blog post at electronicsforu.com

 

 

WORKING:

 

Two important points to consider in IC ne555 timer:

 

A. Output or Pin 3  of 555 timer will be 1(HIGH) only when the voltage at pin 2  or trigger pin is less than 1/3v of the applied voltage at Vcc pin of 555. 

Since battery is of 9 volts, hence : 

1/3 of 9 = 3 volts

 

B. Capacitor (100 uf) discharges through discharge pin (7th) to ground as soon as the voltage at pin 6 or threshold pin of 555 timer is greater than 2/3v of the applied voltage at the 8th pin or Vcc pin.

2/3 of 9 = 6 volts

 

Connect ends of a wire or circuit (whose continuity you want to check) to respective C.P:

CASE1 – When there is a break in the circuit

In this case, all voltage drops across open circuit(since there is a break) as it acts as an infinite resistor. Due to this, voltage at pin 2 or trigger pin is greater than 1/3 of 9v causing a reset of flip-flop inside the 555 timer and thus zero volt as output. Now since output pin is directly connected to the buzzer, it produces no sound.

 

CASE2- When there is no break in the circuit

In this case resistance between pin2 and GND is 0, so all voltage drops across 4.7k resistor. Due to which voltage at pin 2 or trigger pin is less than 1/3 of 9v causing set of flip-flop inside the 555 timer and thus one as output. Now since output pin is directly connected to the buzzer, it produces a beep sound.

 

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