Keep note, the signal produced here comes from the natural ability of the coil and the capacitor across it, and hardly needs any other components.
The tuned circuit (a coil plus a capacitor across it) formed here generates a smooth sine wave signal. The single turn (1T) feedback coil (L1) is routed to the base of Q1 via C2, and base of Q1 is biased by R1 while end of the coil (50T) wired directly to the collector of Q1.
Following is a very concise explanation, so this session is best read along with the tutorial Both items together will help your understanding of the metal detector circuits.Īs pointed out earlier, the sensor-head of the circuit is a 50 turns (25T top + 25T bottom) ‘printed’ coil tapped at first turn. The working principle of the non-contact metal detector module is not very hard to understand. This is the photograph of the second version (I don’t have one handy yet): In this near-identical design, you can see an annunciator LED too. Next is the schematic of another version of the metal detector module that has a circular coil etched on the printed circuit board. Here is the basic schematic of the metal detector module.
The sounder in the module is a standard active piezo-buzzer, and there’s also a small trimpot to fine-tune the circuit. Pretty nice!Ī handful of commonly available discrete components remain including three bipolar junction transistors, a few resistors, and capacitors. The coil starts at the top side of the double-sided printed circuit board and makes square loops towards the center, A via in the center of the printed circuit board takes the coil to the other side of the printed circuit board and the same set of tracks are on the bottom side. a single coil with a precise tapping at one turn. If you look very carefully at the printed circuit board, you can see that the rectangular coil is tapped at one turn i.e. The clever part of the design is the single rectangular coil made by etching one continuous track on the printed circuit board. In this concise primer you will have the schematic and all other details you need to know if you want to make a simple metal detector on your own.
The cheap module I received from China had no instruction manual or circuit diagram, so I had to do a lengthy Google search in order to get its basic schematic. A while ago I bought this non-contact metal detector module from an online store to see how it functions, and what I need to build it.