[Dzl] starts his write up with an explanation of how most oscillator based metal detectors work. This one differs by using an Arduino to read from the metal detecting coil. The circuit starts with ...

Compared to the simple diode needed to demodulate AM radio signals, the detector circuits used for FM are ... at the zero-crossing point. Since the frequency of the modulated carrier changes ...

Therefore, a current measurement technique, especially a high frequency di/dt measurement technique ... Block diagram of the di/dt detector circuit. The bold lines represent outside devices. IP[4].