DIY Voltage Detection Pen

What is a voltage detection pen?

A voltage detection is exactly as it sounds. The pen will light up when voltage is present. You can use a voltage detection pen to test if wires have voltage in. This is useful in the electrical installation industry as a quick check to see if there is any power on wires that electricians may want to work on.

How it works

A voltage detection pen works by sensing small magnetic fields around wires. All wires have a small magnetic field around them when current is flowing the magnetic field depends upon the type of current passing though it.

The pen can only detect AC voltages as DC has static fields that do not induce a current where as AC voltages do induce a current.

The circuit works by using a small coil of wire that will pick up the small magnetic field, the coil gets induced with a small current and activates the transistor. The circuit uses 3 transistors as the small amount of current though the first transistor is not enough to light the led. The current increases thought the second resistor due to the gain of the transistor. The transistors I used were the 2n2222 these have a gain of roughly 300 this data can be found in the datasheet.

The emitter of the first transistor goes to the base of the second transistor then the emitter of the second transistor into the base of the third transistor.

Build your own

To build your own you will need three NPN transisors I used 2n2222 transistors, 1M, 100K, 330ohm resistors, an LED and a battery. You may wish to add a switch to save the battery when it is not being used.

I build the project on a small piece of perfboard, so all you have to do is solder all the parts on to the board by following the schematic.

To make the coil for the antenna I wound a small piece of single core wire around a tip of a screw driver but you could use anything that is roughly 4mm in diameter.

I designed a 3d printable enclosure for the pen if you wish to use it. But please bare in mind that I have not printed the case my self as I am doing the project as a proof of concept but if you wish to use the finished product I would recommend making an enclosure for it. The parts should simply clip together, I have attached a STL file if you want to use it.

How to use the pen

To use the voltage detection pen all you need to do is press the button on the pen (if you added one) and bring the tip of the pen near to a conductor and if voltage is present the LED will light up.

Acknowledgement

I thank PCBWay & LCSC Electronics for the partnership.

PCBWay Is a cheap reliable service where you can get your PCBs manufactured. All the PCBs are high quality and the engineers are very helpful and will resolve any problems you may have quickly. Sign up today and get a $5 welcome bonus. Check Out PCBWay Hackster page.

LCSC Electronics Is China's leading Electronic Components Distributor. LCSC sells a wide variety of high quality electronic components at low prices. With over 150, 000 parts in stock they should have the components you need for your next project. Sign up today and get $8 off on your first order.

Website

Check out more of my other projects on my website.