Crystal radios are famous for doing something almost magical: picking up broadcast signals with nothing more than a diode, an antenna, and a pair of headphones. They’re the simplest RF receivers you can build — and a brilliant way to learn how radio waves become electrical signals.
In this post, I’m taking that idea into the modern world. Using just two components — a high-speed Schottky diode and an LED — you can build a tiny “crystal detector” that responds to 2.4 GHz Wi-Fi, Bluetooth, and even microwave oven leakage. Unlike classic crystal radios, it doesn’t rely on a nearby AM transmitter, long wire antenna, or earth ground. Just the diode, the LED, and a small piece of metal for an antenna.
Despite the simplicity, it’s surprisingly effective. Bring it near a phone, router, laptop, or microwave oven and you’ll see packets and bursts appear as quick flashes of light. It’s easy to demonstrate in a classroom, easy to experiment with, and a great hands-on way to show how rectification and RF envelope detection work at microwave frequencies.
This circuit has a very minimal bill of materials, and does not require any soldering to complete, making it a great fit for a class-room activity.
Parts you’ll need
1× 1N5711 Schottky diode (AliExpress | Amazon)
(AliExpress | Amazon) 1× Red LED (AliExpress | Amazon)
Assembly Instructions
Bend the LED legs so they extend horizontally in opposite directions. These form the antenna.
so they extend horizontally in opposite directions. These form the antenna. Place the diode alongside the LED , with its legs parallel to the LED legs. Make sure the diode’s cathode is next to the LED’s anode .
... continue reading