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Hi guys,
I've built the Baracuda I bought as a kit from Silverdog and have spent quite some time making a control box, shaft and coil for it. At first I almost gave up on it because it wouldn't detect anything; just made annoying beeps until I spotted on here where someone had asked if it should work on 9V or 12V. Since the kit came with a PP3 battery clip I thought it should use a 9V supply, but when I connected a 12V battery it all worked fine.
After turning the circuit board into a fully functioning metal detector, I took it to the beach today for its first test run. I immediately discovered that it was giving false signals all the time. I'd set the Threshold pot to the point where there was *just* a discernible tone and found that it beeped every time the coil bumped into a ripple in the sand or the direction of the coil changed at the end of a swing. I couldn't stop it from doing that unless I turned the Threshold right up, and even then it would still do it on occasions.
In trials at home I was able to detect my gold wedding ring in air at 20" (very faint, but definitely there,) a £1 coin at about 18" and smaller clad steel coins at various distances, so I was quite pleased with that. I'd done the voltage setting to zero thing (but with a different coil) but lacking the equipment couldn't set the Delay pot so I set it for best range by empirical means.
I did find today that by moving the coil slowly I could lose some of the noise, so attached my wedding ring to a length of paracord, dug a hole about 18" deep and buried it in the sand. By pulling on the paracord I was able to move it up in the sand until it was being detected at about 9", but that was with the Threshold set high.
I carried on detecting for a while but found only iron - an 18" length of rebar (reinforcing rod,) a child's metal spade and a bottle cap but there's no saying that there was anything else there. If there's nothing there that's exactly what I'll find . . .
So the Baracuda shows promise, but requires some work to make it a viable beach detector, and I would be grateful for any advice on how to achieve that.
I made my coil housing from 16 bar uPVC 20mm dia pipe bent into an 11" circle, joined with a cemented tee. I threaded about 75' of 0.5mm enamelled copper wire though it down the branch of the tee, 'fishing' it round with a small nut on a length of string attached to the free end, and a powerful magnet pulling the nut round from the outside. Don't ask me how I kept the kinks out of the wire - I'm trying to forget . . .
When that was done I connected my LC meter to it and found that the inductance was 600uH, so I removed one turn at a time until I got it down to 463uH and about 5pF, with a DC resistance of 1.5 ohms, so it's in the right ballpark electrically. I then soldered a length of RG-58 coax to it and filled the coil housing with expanding foam from an aerosol can to stop the wire from moving inside the housing. The coax has a PL259 plug on the end which fits an SO239 socket on the control box so I can use different coils easily. The coil isn't shielded because it's impossible to shield it inside a sealed circular housing, but I do have an un-housed 11" shielded coil I made - but I need to make a housing before I can try it and see if it makes a difference.
One question that does occur to me is if it's possible to shield the existing water pipe housing on the outside? I have some self-adhesive aluminium tape which I could apply and then bind it with bare copper wire which I could then connect to 0V *somehow*. I don't really want to scrap that coil as it's taken a lot of making - even to the extent of a friend having a specially designed bracket 3D printed to suit . . .
Any and all advice welcome and gratefully received. TIA
I've built the Baracuda I bought as a kit from Silverdog and have spent quite some time making a control box, shaft and coil for it. At first I almost gave up on it because it wouldn't detect anything; just made annoying beeps until I spotted on here where someone had asked if it should work on 9V or 12V. Since the kit came with a PP3 battery clip I thought it should use a 9V supply, but when I connected a 12V battery it all worked fine.
After turning the circuit board into a fully functioning metal detector, I took it to the beach today for its first test run. I immediately discovered that it was giving false signals all the time. I'd set the Threshold pot to the point where there was *just* a discernible tone and found that it beeped every time the coil bumped into a ripple in the sand or the direction of the coil changed at the end of a swing. I couldn't stop it from doing that unless I turned the Threshold right up, and even then it would still do it on occasions.
In trials at home I was able to detect my gold wedding ring in air at 20" (very faint, but definitely there,) a £1 coin at about 18" and smaller clad steel coins at various distances, so I was quite pleased with that. I'd done the voltage setting to zero thing (but with a different coil) but lacking the equipment couldn't set the Delay pot so I set it for best range by empirical means.
I did find today that by moving the coil slowly I could lose some of the noise, so attached my wedding ring to a length of paracord, dug a hole about 18" deep and buried it in the sand. By pulling on the paracord I was able to move it up in the sand until it was being detected at about 9", but that was with the Threshold set high.
I carried on detecting for a while but found only iron - an 18" length of rebar (reinforcing rod,) a child's metal spade and a bottle cap but there's no saying that there was anything else there. If there's nothing there that's exactly what I'll find . . .
So the Baracuda shows promise, but requires some work to make it a viable beach detector, and I would be grateful for any advice on how to achieve that.
I made my coil housing from 16 bar uPVC 20mm dia pipe bent into an 11" circle, joined with a cemented tee. I threaded about 75' of 0.5mm enamelled copper wire though it down the branch of the tee, 'fishing' it round with a small nut on a length of string attached to the free end, and a powerful magnet pulling the nut round from the outside. Don't ask me how I kept the kinks out of the wire - I'm trying to forget . . .
When that was done I connected my LC meter to it and found that the inductance was 600uH, so I removed one turn at a time until I got it down to 463uH and about 5pF, with a DC resistance of 1.5 ohms, so it's in the right ballpark electrically. I then soldered a length of RG-58 coax to it and filled the coil housing with expanding foam from an aerosol can to stop the wire from moving inside the housing. The coax has a PL259 plug on the end which fits an SO239 socket on the control box so I can use different coils easily. The coil isn't shielded because it's impossible to shield it inside a sealed circular housing, but I do have an un-housed 11" shielded coil I made - but I need to make a housing before I can try it and see if it makes a difference.
One question that does occur to me is if it's possible to shield the existing water pipe housing on the outside? I have some self-adhesive aluminium tape which I could apply and then bind it with bare copper wire which I could then connect to 0V *somehow*. I don't really want to scrap that coil as it's taken a lot of making - even to the extent of a friend having a specially designed bracket 3D printed to suit . . .
Any and all advice welcome and gratefully received. TIA
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