First of all, continuity testing is very important in electronics work.
It helps to find broken wires easily and it also helps to check PCB tracks.
Sometimes wires look good but inside they are broken, so continuity tester is used.
In this project, a simple Continuity Tester Circuit using Op-Amp is designed.
It uses IC 741 op-amp and it also uses a buzzer and an LED.
When continuity is present the buzzer makes sounds and at the same time the LED glows.
Therefore, user can hear and see the result easily.
Circuit Working:
Parts List:
| Components | Value | Quantity |
|---|---|---|
| Resistors | 22k | 2 |
| 10Ω, 470k, 2.2k | 1 each | |
| 1k | 3 | |
| Preset 10k | 1 | |
| Capacitor | Electrolytic 10uF 25V | 1 |
| Semiconductors | IC 741 Op-Amp | 1 |
| Transistor 2N2222 | 1 | |
| LED any color | 1 | |
| Diodes 1N4148 | 3 | |
| 6V to 9V DC Buzzer | 1 | |
| ON/OFF Switch | 1 | |
| 9V Battery | 1 | |
| Probes sharp metal with short flexible wires | 2 |
This circuit works using a voltage comparator principle.
First, the probes are connected to the test point and IC 741 compares probe voltage.
Then power switch S1 is turned ON and if probes touch a good conductor then current flows.
As a result a voltage appears at op-amp input.
Now IC 741 compares this voltage with reference voltage.
If continuity is detected then output of IC goes high.
Next, diodes D1 to D3 conduct and then base current flows to transistor Q1.
After that transistor turns ON and so the buzzer gets power and sounds.
At the same time the LED glows which therefore, confirms the continuity.
If wire is broken then no voltage appears.
Hence, op-amp output remains LOW and so transistor stays OFF and thus a buzzer and LED stay OFF.
How to Build:
To build a Continuity Tester Circuit using Op-Amp following are the steps required for connection:
- First, start the circuit by collecting all the parts as shown in circuit diagram.
- Then IC 741 pin 7 is connected to positive supply.
- Pin 4 is connected to ground.
- Pin 2 is inverting input which connects to VR1 and resistor network.
- Pin 3 is non-inverting input and connects to probe through resistors network.
- Pin 6 is output pin and it connects to diode chain D1 to D3.
- Transistor 2N2222 emitter pin connects to ground.
- Collector pin is connected to buzzer and LED and resistor R8.
- Base pin is connected to op-amp output through R7.
- Buzzer positive terminal connects to supply.
- Negative terminal connects to Q1 transistor collector pin.
- Power Supply 9V battery positive goes to switch S1.
- At last, battery negative goes to ground line.
Conclusion:
Finally, this Continuity Tester Circuit using Op-Amp is simple and reliable.
It is easy to build at home as it uses very few components.
It gives both sound and light indication.
Therefore, it is useful for beginners and technicians and it helps in quick fault finding.
Hence, this circuit is a good practical project.