Small inductance changes on the order of 0.01% can easily be sensed over a wide range with a simple circuit connected to a serial port (see the figure). Using a classic Colpitts oscillator interfaced ...

We’ve read a lot about oscillators, but crystal oscillators seem to be a bit of a mystery. Hobby-level books tend to say, build a circuit like this and then mess with it until it oscillates.

This is a common emitter Colpitts oscillator. R1 and R2 form a voltage divider to provide base bias. the emitter resistor R3 also provides some bias. R4 is the collector resisotr across which the any ...