18-11-2020, 12:20 PM
41
Re: Foxy's Latest Project.
Originally Posted by OldGreyFox
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You're a star Besoeker.....
I've always thought that you and me had a lot to talk about.....
I have a bunch of resistors, mostly 0.5 ohm 5%, a few wire wounds, some ICs, some caps, scope leads. I also have a 100 MHz real time Tektronix oscilloscope and a few 1:1 and 10
robes.I have a clip on current probe. It's a HEME 1000 Ammeter, a fine piece of kit. Probably not a use for you but if you want it that's OK.
18-11-2020, 12:21 PM
42
Re: Foxy's Latest Project.
Before setting about building the circuit it was necessary to construct the search coil. I had already made a coil winding apparatus for construction of the mark 1 detector, so with a little modification was able to use it for the MK2 coil as seen in the photo....This coil is very different to the ones I have wound previously. It is larger (200mm dia) and must be covered with aluminium foil. As you can see, the coil has now been wound and is being covered with an insulating material before the application of the foil. I will figure out how this can be tidied up and attached to a supporting ring fitted to the end of the shaft later.
There are some specialised items required for this model, and rather than forage around in my extensive collection of recycled components, I decided to remove any doubt as to their ability by purchasing some new bits......They arrived yesterday.....
These is not a complete list, and there are still some capacitors and assorted hardware required that I might already have in stock, but if I have, the whole lot has only come to less than twenty quid...
18-11-2020, 12:31 PM
43
Re: Foxy's Latest Project.
Originally Posted by Besoeker
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OK Foxy.I have a bunch of resistors, mostly 0.5 ohm 5%, a few wire wounds, some ICs, some caps, scope leads. I also have a 100 MHz real time Tektronix oscilloscope and a few 1:1 and 10
robes.I have a clip on current probe. It's a HEME 1000 Ammeter, a fine piece of kit. Probably not a use for you but if you want it that's OK.
18-11-2020, 12:50 PM
44
Re: Foxy's Latest Project.
Originally Posted by OldGreyFox
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Yes sorry Mart, I forgot to label 'IC 1'...And the detecting end of things is the coil marked 'L1' next to the diode....The dotted grey line separates the first stage from the second stage. The first stage is an oscillator based on a 555 timer chip and sets up a pulse frequency that is sent into the ground through the coil L1. When the pulse returns it is collected in the coil as a magnetic disturbance created by any metal it has come into contact with below ground. The magnetic disturbance is separated by the MOSFET and passed on to IC2 which is an operational amplifier which also acts as a comparator and sends the signal on to a final stage of amplification provided by Q3, which can be heard in the speaker....
The pot looks as though it sets the feedback for the op amp and therefore the sensitivity of the detector. Is that right?Edit: How many turns does the coil need to have?
18-11-2020, 02:20 PM
45
Re: Foxy's Latest Project.
Originally Posted by OldGreyFox
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They sound great Besoeker, although the 1000 Ammeter might be a little overkill for small electronic circuits. How much do you want for the items, because the oscilloscope won't have come cheap....
There is also a CEN-TECH multi meter. Volts, Amps, Ohms, NPN/PNP meter.
Yes, I didn't think the Ammeter would float your boat............
Nor the 4.5 kV scope probes...........
18-11-2020, 04:01 PM
47
Re: Foxy's Latest Project.
Originally Posted by mart
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I've still got my dual-beam scope but no probes. I was offered £200 for it when I stopped work. I thought I might need it but never have. Should'a took the money.
18-11-2020, 09:21 PM
50
Re: Foxy's Latest Project.
Originally Posted by mart
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Thanks I sort of understand that ..well, maybe as much as anyone can who hasn't looked into metal detectors before. The pot looks as though it sets the feedback for the op amp and therefore the sensitivity of the detector. Is that right?Edit: How many turns does the coil need to have?
The coil was made up of 25 turns of 24 SWG enameled copper wire, and should be covered with Aluminium Foil.
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