HOW TO MAKE A CONTINUITY TESTER 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.
555 timer is one of the most common and 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 for this project:
2. one buzzer
3.capacitors 100uf and .01uf
5. resistors 4.7k and 47k
*C.P = Connecting Probe
|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|
|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|
Two important points to consider in a 555 timer:
A. Output or Pin 3 of 555 timer will be 1(HIGH) only when 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 volt, hence :
|1/3 of 9 = 3 volts|
B. Capacitor (100 uf) discharges through discharge pin (7th) to ground as soon as voltage at 6 pin or threshold pin of 555 timer is greater than 2/3v of the applied voltage at 8 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 circuit
In this case, all voltage drops across open circuit(since there is 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 reset of flip-flop inside the 555 timer and thus zero volt as output. Now since output pin is directly connected to buzzer, it produces no sound.
CASE2- When there is no break in 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 buzzer, it produces beep sound.