Wednesday, February 25, 2009

New Metal Detector

I've never been as popular as I have been dead. Perhaps the recent rumour of my death had something to do with my much reduced electronics output. To mark this occasion, I have designed a new embodiment of the CCO (Coil Coupled Operation) metal detector, a new genre which I invented in 2004. I believe that 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 less than ten 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 (


jare said...

Hi Mister Thomas.CCO metal detector are very good.Sensitivity discrimination and very good, but the maximum range that I made the 150mm.What is your idea to make what kind of CCO to reach at least 300mm depth?

Thomas Scarborough said...

Thanks Jare. I'm pleased the metal detector fulfilled its promise. 30cm is an extreme depth for any metal detector. Besides, are you sure you ever want to dig that deep? ;-) Try the Geotech Tech Forum for some great free designs. I managed to push the CCO principle to more than 20cm, but that design is copyright Elektor.

jare said...

Thank you mister Thomas for the advice but CCO metal detector from Elektor-Magazine July/August 2005,detected old victorian peny at 180mm.CCO metal detector that I made.