would like to build my own metal detector have a few questions

I would like to build my own detector. I wont have any problems putting one together, as far as soldering etc. My questions  are about which one to build? I know I want to build a PI type. I have seen diagrams to a few of them. I have not yet seen the goldscan yet. I still need a few more posts to download stuff. In the meantime tell me which one you think is the best homebuilt highly sensitive detector. For detecting general purpose use or high class type with bells and whistles. I only plan on looking for coins, gold. I don't have a lot of time to build anymore so would hate to waste my time building something only to find out there is a better circuit that will produce better results. I usually end up modifying whatever I build, so starting off with a good circuit helps. I know about the fast loops etc. I am just interested in the electronics. For the fun of it I want to try a new loop design. I know you have heard that before. doesn't matter that's the fun of building your own stuff, you can do whatever you want, within reason of course. So just for reference I am asking these questions with an 8 inch coil in mind. Once again your opinion counts here. Which homebuilt is the best, most producing detector? Is it the frequency it operates on or why  do you think it is? Is it by experience from actually trying one of those homebuilt ones?
Thanks


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Take a look in here:

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This guy puts kits together based on documented projects on the forums.

Your lucky if you can come up with the parts for the prices he ask.  The boards are GOOD quality.

PM him here and he will give you the Dollar amount.     User Name Silverdog.   I sent him cash and it got here in two weeks.  

Not Bad, Eaaa?

I got the Surf PI Kit from him and If I had the funds would get a second.

All info you would need is documented here or on the other major builders site.





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I think I have what I need now. From what I can tell the PI circuitry is all about the same, same style. The one that intrigues me I guess is the Blind Squirrel. Simply because he took and got rid of the two 555 ics found in other units and used a single ic for that and another single that would have taken another two 555's. Comparing to the two coil unit I saw that was popular. had about 4 555 timer ics. what I will be doing is modifying the circuit. Don't ask why, just because. Cant say it will be better but I have to try. First I will change the IC U3 to another flavor hopefully for improvement. The 318 has a slew rate of 70v/µs and as high as 150v/µs. voltage gain of 200. The one I have chosen will have a slew rate of 600v/µs a voltage gain of about 10,000 or about 80 db. I Will tame it down a bit in my circuit but I will make it variable until I find the sweet spot. There is a voltage difference though, the lm318 will output much more voltage but then again it will need more to operate. The one I have chosen to try is the OPA2846 which operates off of 5 volts. It is a dual unit so I will have to op amps to play with. I plan on eliminating the cd4536b in the circuit and use a simple variable generator with variable frequency. That way I am not tied down to just a few frequencies. I have chosen a simple frequency readout which I have already built which will show me the exact frequency I am using. It does bring up the cost slightly. I have a few other ideas but I think the important thing is to get it up and running first then I will further make add ons for it.  One of the further improvement will be in the coil design, and I know you heard it all but that's part of the fun of building. I would like to design a coil that will act like a 2 inch coil by itself a 6 inch and say an 8 inch. For the bigger plug in coil say 8 inch -10 inch -12 and 14 inch all in one. Each coil working independently of the other at the same time, well almost. I would like to hear what you like in a metal detector that really doesn't exist? Also If you just have any ideas or thoughts let me know. I just like to experiment. cant say I can build this overnight cause I am limited on time but given a month or two I think I can. The hard part is the coil design and switching circuitry. This should prove interesting. I will keep going until it works. Have to start with one coil first to get unit working, but I will include the circuitry for all coils. Don't ask for the diagram yet as that has to be determined by the final design that works. I don't have one put together yet, only in my mind. I am a beginner metal detector hunter but I am not a beginner at electronics. So input from you is valuable in the help of what one might want from a detector. This is a PI type I am building. It will have a few bells and whistles others don't only to be able to see the effect of what it might do. It is necessary for me to do so to come up with a final circuit that will more basic. I am out to make a sensitive detector that you can control. One that is sensitive up close and at a distance. One that gives me more control over the circuitry and one that has something unique about it that everyone will want to try.

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http://www.thunting.com/smf/index.php/topic,25626.msg182205.html#msg182205

Good looking build there SvenS!   Thank you.  What Connector did you use for the coil?

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http://www.thunting.com/smf/index.php/topic,25626.msg182227.html#msg182227

Nice work there SvenS

Regards xavier

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Xavier