In this tutorial, we are going to make a “Non-Contact AC Voltage Detector Circuit”. In a traditional voltage tester, we need to touch live wire physically with a metallic tip. So, to test AC mains Non-contact voltage detectors are a much safer way and it reduces the risk of electric shocks while working in high-voltage situations. Here we design a simple circuit based on NPN transistors like BC547 with a few easily available components, it can produce visual and sound alerts during the detection of AC supply on the wire.
We can identify the presence of AC voltage in the wire by using this simple Non-Contact AC voltage detector circuit or we can use it as a wire tracker, which also helps to detect broken supply wires. For identifying the leakage current on active live wires this circuit has an antenna. The leakage current flows through the antenna and is fed to a very high-gain amplifier. The amplifier output goes high when it detects weak electrical signals. The amplified voltage can be interfaced with LED or buzzer. This circuit may not detect DC supply wire.
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | Transistor | BC547 | 3 |
| 2. | LED | – | 1 |
| 3. | Resistor | 1MΩ, 100KΩ, 100Ω | 1,1,1 |
| 4. | Buzzer | 5V | 1 |
| 5. | Switch | – | 1 |
| 6. | Connecting Wires | – | – |
| 7. | Battery | 9V | 1 |
Circuit Diagram
Transistor BC547 Pin Configuration
Working Explanation
For this circuit we can use a small copper plate or wire spiral as an EMF detector, the wire spiral can be made from 15cm insulated wire should not touch the spiral wire or bare hand on the AC supply carrying wire, Be extremely careful when you handle high volt AC supply. Here as we can see in the circuit, the main part of this simple AC voltage detector is a transistor, it operates as an amplifier and switch, Buzzer produces a sound alert when the wire spiral detects the EMF (electromagnetic field) on the AC supply carrying wire, LED also glows to indicate the AC supply detection.
In this circuit, three stages are constructed with BC547. Which is a very high gain amplifier connected in the Darlington pair configuration. Here transistor Q3 base is connected with a wire spiral and it will detect EMF on the AC supply carrying wire, and then the signal from the Q3 transistor is given to the Q2 transistor base. This Q2 gets a large bias than Q3 and so it can amplify the input signal and gives it to the Q1 transistor base. Here the Q1 transistor acts as a switch and when the signal reaches its base, it becomes a closed switch and connects to the buzzer, LED with bias if no signal then Q1 stays in off condition. It gives visual and audio responses. The LED lights up and the speaker buzz when it detects the presence of active mains live wires.
Applications
Can be used in high AC voltage lines as a wire tracker, and also helps to detect broken supply wires.
