Simple Non Contact AC Mains Voltage Detector Circuit

This Simple Non Contact AC Mains Voltage Detector Circuit is to find AC voltage without touching wire.

It uses antenna to catch AC signal from air.

Then signal goes through transistors and LED blink when AC voltage is near.

This circuit is good for safety and easy to make at home.

WARNING: Even with this tool always be careful with electricity.

If someone have problem making this circuit better call a good electrician.

Circuit Working:

Parts List:

Antenna catch AC signal from air this AC voltage make small current in antenna.

Antenna connect to base of first transistor Q1.

When AC voltage come to antenna it makes small current in base of Q1.

Q1 make this signal bigger and its emitter follow that signal.

Emitter of Q1 connects to base of Q2 and this make signal more strong.

Q2 work like emitter follower and it have a high input impedance.

Emitter of Q2 connects to base of Q3 which then helps signal get more boost.

Q3 is last transistor and is also a emitter follower which give high output impedance.

Collector of Q3 connect to LED with one resistor to stop too much current.

When AC voltage comes near the antenna then LED turns ON.

LED show that AC voltage is near the antenna.

Formulas:

These easy formulas help to make and understand non-contact AC mains voltage detector circuit using transistors.

Q1 (R1) Collector Resistor:

For red LED resistor R1 connect with LED and Q1 collector.

It control the current for LED and keep it safe between 10 to 20 mA.

Use ohms law to find R1:

R1 = (Vcc − VLED) / ILED

where:

• Vcc is 9V battery.
• VLED is LED forward voltage drop around 1.8V for red LED.
• ILED is current for LED like 10 mA = 0.01 A.

These formulas help to understand better and improve circuit design.

It depend on what components we have and what our project needs.

We can also change values a bit after testing and based on parts we use.

How to Build:

Below are the steps to build a Simple Non Contact AC Mains Voltage Detector Circuit:

• Put three BC547 transistors on the PCB.
• Connect collector of all transistors to positive supply with resistors.
• Other side of resistors connects to 9V battery positive side.
• Connect emitter of Q1 to 9V battery negative side.
• Connect emitter of Q2 to base of Q1.
• Connect emitter of Q3 to base of Q2.
• Connect collector of Q1 to LED cathode short leg.
• Connect anode of LED long leg to positive supply.
• Connect base of Q3 to antenna wire or metal.
• Connect 9V battery positive to PCB positive line.
• Connect 9V battery negative to PCB GND line.

Testing:

• Power the circuit with battery.
• If AC voltage comes near the antenna then LED will blink.

Important details:

• Always check transistor pinouts two times and be sure they connect right way.
• Choose resistor values based on LED and transistor need.
• Try different antenna size and position to make it more sensitive.
• This circuit is simple but resistor values may change based on parts we use.
• Better to look at datasheets for correct details of our components.
• Be careful when working with electricity its always good to follow safety rules.

Conclusion:

This Simple Non Contact AC Mains Voltage Detector Circuit can find AC mains voltage without touching wire.

Antenna catch AC signal from air.

Signal connects through 3 transistors and then LED will blink if AC voltage is near.

This type of non-contact AC voltage detector help to find live wire or power source without touching.

References:

AC Mains contactless detection with DIGITAL