Microwave Detector

Date completed: 2014

This is another device constructed for school Physics teaching. It demonstrates well that microwaves are emitted (and a few escape) from a microwave oven and also from a mobile phone by sounding a buzzer and lighting a red LED (once the variable resistor is adjusted just above the continuous background noise.) You even hear the characteristic rhythm of the mobile phone connection: tum-tum-tee-tum!

Photo and School instructions

Design

I can't tell you much about how this works, except that it has an oscillator made from an op amp (half of a 741) and a capacitor, which can be made unstable by the adjustment of the variable resistor. This somehow then picks up any radio noise nearby (acting as a weak aerial, I suppose) and the resulting oscillations are then amplified (and saturated) by another op amp with a very high gain (no feedback.) I must have found the circuit or a similar one on the internet somewhere!

Circuit Diagrams

Tiny CAD (.dsn) file: Microwave Detector