Build an AC Current Detector Using a Pair of Transistors and Junk Drawer Items
The Wireless AC Current Detector was designed using several transistors, a ballpoint pen spring, LED, and a 9V battery.
It’s incredible what can be made with things we usually have just lying around, more so when you can make useful tools out of them. That’s the idea behind maker New Pew’s Wireless AC Current Detector, who used some transistors leftover from a previous project, along with knowledge about their properties. In this case, it’s known as the Darlington configuration, which is when a circuit includes a multi-transistor configuration in a compound structure made by a pair of bipolar transistors. The transistors are connected in such a way that the current amplified by the first transistor is amplified further by the second (*more on this in a bit).
New Pew created the AC current detector using several transistors, including a pair of BC547 transistors, a 220 Ohm transistor, a ballpoint pen spring, an LED, and a 9V battery. New Pew details how the detector works, and the Darlington configuration comes into play. “In this circuit, an antenna (spring) is connected to the base of the first transistor. When we place this antenna near an object that is AC energized, a small current gets induced into the antenna due to electromagnetic induction. This current triggers the first transistor. Output of the first transistor triggers the second. The second transistor switches on the LED, indicating that AC voltage is present.”
New Pew’s design is simplistic, but it works, and it works well for its intended use. The setup is self-contained on a removable battery clip, so it can be attached to a new battery when needed, making it easy to use. New Pew has uploaded a detailed walkthrough on his project page for those who would like to recreate his build.