Simple Smartphone Metal Detector Experiments

This time I will try to describe the principle of operation of a simple Metal detectors in which data is processed by a smartphone. The main principle of this detectors consists of LC oscillator which serves as a reference, and on the other side a smartphone application, which is basically a frequency meter. When we put a metal object near to the coil the frequency changes and application detect the change and signalize that there is are metal object near the coil.
The oscillator consists of a parallel LC oscillator circuit and two transistors. I also put two trimmer potentiometers instead of resistors so we can change the amplitude and partial shape of the signal to make it easier to process in the smartphone app. Let me mention that in this experiment I use the great apps of the Neco Desarrollo team "Smart Hunter" and "MFM3 Pinpointer" which are the only Android apps of this kind in the World.
Specifically, my coil consists of two windings connected in series, the larger one with a diameter of 23 cm, and the smaller one with 12 cm. Both are wound with lacquered wire with a diameter of 0.4 mm and contain 25 turns each. It is important that the resonant frequency of the parallel LC circuit is in the range of 4Kz to 20KHz so that it can be processed by the Smartphone. With "+" and "-" Buttons we can change Sensivity of the detector. To have an audio indication I connected the Power Amplifier to the output of the headphone jack.
There is another very interesting application, "MFM3 Pinpointer". This is also a Metal Detector application that can distinguish between ferrous or nonferrous materials.
Finally, let me conclude that this is a very simple version of a metal detector, so it does not have any great sensitivity, but it serves well for educational purposes. To emphasize that it is very unstable, the frequency depends a lot on the temperature, so more frequent calibration is needed. In my previous videos I have presented almost all the metal detectors by Neco Desarrollo or their variations so if you want to make one of them, you can watch them.

Detailed instructions, and schematic diagram at:
https://www.hackster.io/mircemk/simpl...

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If you are interested in this area, see the Playlist with all my Metal Detectors at:
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