New CCO Metal Detector

Thomas Scarborough has designed a new embodiment of the CCO (Coil Coupled Operation) metal detector, a new genre which he invented in 2004. This is the first IC design to appear on the Internet (there is a transistor design on many websites, and IC designs were published by Elektor and EPE). It took me just eight minutes to design this — which illustrates the simplicity of the principle.

OBSERVATION: On the surface of it, it may look like an IB (Induction Balance) detector — but it is not. It works on the principle of the transformer coupled oscillator (TCO), and requires an AM radio to generate a beat frequency in the speaker. This means that it (also) works on the beat frequency operation (BFO) principle. However, it is not a BFO detector either, for the simple reason that it has two coils instead of one — and it is far more sensitive. With this circuit, I obtained a one-tone shift in an AM radio speaker at 15 cm (6 inches) with a 27mm (1 inch) diameter coin. This is what you should aim for. You can find details of the construction of the (identical) coils L1 and L2 at These should be fixed to a search plate (e.g. hardboard, with cable ties). Note that the orientation of the coils matters: you might need to flip one of them over for best performance. This is an experimental design: experiment with the coils overlap, experiment with the AM radio frequency (you should tune in to a clear whistle, not a hiss, and find the “zero beat” zone), and you might even experiment with C2, or the size and shape of the coils. A screened wire may be taken to the AM radio aerial as shown — if a connecting wire is required at all. Click on the diagram to enlarge. Click on the “Electronics” category top left to follow the electronics trail on this blog.

NOTE: You may re-publish this design, on condition that you acknowledge the designer (Thomas Scarborough) and this blog

One thought on “New CCO Metal Detector

  1. Rudolf


    how much mH does the coil have and which oszilation frequency is used?

    When I place the faraday between the coils, the oszilation stopps. Is one shield maybe over both coils so they can exchange over field internaly?


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