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Originally Posted by Fred
I hope that by finishing reverse-engineering and possibly simulating the circuit we will be able to understand more about its function.
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There isn't much to reverse engineer. When you have an accurate circuit diagram, you can make a clean schematic that will be easy to understand. The hard part is the missing search head design. There are two problems with this:
1. You don't have a clue what components are in the search head, or the values of those components.
2. If you did know the components and their values, I would think you could not build a copy that works unless you are lucky. The reason is because I suspect there is a tuning procedure needed in order to make the circuitry operational. With any luck, if you had the components for the search head connected to a working circuit, the pistol may give some sort of reading. If it does, then you can further tune some of the components for better response, or even use test equipment if you know what you are trying to tune for. I have a feeling the physical positioning of the coil and other apparatus in the search head may be critical, similar to how the physical positioning of some conventional search coils is (ie: DD coils).
The real missing info is about the theory of circuit and how it interacts with the coil and other search head parts. It would be good to to first have an understanding of what property of the target you are basically searching for, and how the search head components respond to these properties. If you first know these things, then you will find it much easier to tune a similar pistol detector. At present you are playing with a puzzle even if you have all the circuit data.
In any case it looks like an interesting project to experiment with. I have also read other reports of some of these pistols getting some medium range signals which are better than a conventional metal detector.
Best wishes,
J_P