Simple EMI Sensor

We are living in a world full of electricity. Even though this electricity is generated, transported and used fairly efficiently, there are always losses in the form of heat, sound or other means. One particular loss is electromagnetic fields. These fields are generated due to current flow. This means that ever device or cable generates these kind of fields. If you amplifies these electromagnetic fields drastically, you can use a LED to visually find out where the field is the strongest.

General project

This project is an extremely simple way to find out where electricity flows. It uses three transistors a few resistors and an LED. The transistors are wired as a Darlington pair, where the emitter of the first transistor is connected to the second. The result of this is that the gain of the transistors is multiplied. This circuit uses this principle twice, so the total gain of the circuit is G=G1 x G2 x G3. Since the gain of these transistors is typically 100, the total gain is around 1,000,000. This means that every signal or noise detected from the antenna will be massively amplified.

Because mains lines transfer alternating current, a magnetic field is generated around these wires. When bringing an antenna close to this field, charges will move. After amplification, a current is generated that can power a LED. Placing the antenna closer to the source will increase the amplified current and increases the LED brightness. Therefore, you can pinpoint the location where the signal is coming from by looking at the brightness of the light. Like mentioned, noise also influences the antenna, so an array of different devices will turn on the LED if the antenna is held close to it.