Metal detector power supply

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Metal detector power supply

Postby Harry Dalek » Wed Jan 01, 2014 10:40 am

Hi a bit off the normal topic here is a circuit thats pretty popular The Hammerhead Pulse induction metal detector

I changed the power supply part using a MC34063 instead of the ic used and did away with the 7805 regulator ..but still using the 7905s as i had these handy .

My Question to any one that wants to have a look at the original here is i find the power supply part a little messy with 5 power rails ...i have simplified the circuit and a little dubious about why it needs 2 negative supply rails..apart from perhaps it using more batteries and keeping the 79s cooler .i just find it messy .

Happy New Year :wink:
Attachments
HHc2 (5).pdf
The hammerhead metal detector
or one of the many versions
(344.38 KiB) Downloaded 209 times
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Postby Steve Anderson » Mon Jan 06, 2014 10:16 pm

I've had a cursory glance at the circuit, I agree it is a mess. However without a reasonably detailed explanation of how it is supposed to work I really can't offer much help. Why the author used gas-guzzling 555;s and 5534's in a portable device is beyond me.

It also requires 12V. If using AA/C/D cells, split them in two (±6V) then two low-dropout regulators...if the supplies need regulating at all. Better still, get it to run on a single +6V rail, this isn't so hard.

There's a whole load of variable/trimmer pots, indicative of poor circuit design.

Good luck, if I can help I will...

Steve A.
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Postby Harry Dalek » Tue Jan 07, 2014 9:11 pm

Steve Anderson wrote:I've had a cursory glance at the circuit, I agree it is a mess. However without a reasonably detailed explanation of how it is supposed to work


Hi Steve bit late but happy new year.

Okay The hammer head pulse induction metal detector has a pdf i will post
a link here for the reason below !
http://www.geotech1.com/cgi-bin/pages/c ... /index.dat


Its a pretty popular one from reading about DIY ones .

Trouble is also its not just one version !

I did a point to point soldering job on it and the number of power rails bound to make a mistake which i did ...

I just redid the power supply over the weekend i didn't end up using the transistor rail splitter in this drawing i just used 2 4.7k and 2 caps in a floating ground before the regulators and that voltage converter ic ...
I suppose i could of just used a 7805 to replace the converter chip...


I really can't offer much help. Why the author used gas-guzzling 555;s and 5534's in a portable device is beyond me.


Well Steve what i have noticed the metal detecting crowd do not have a Steve Gary or Klaas ! to put it nicely i think evolution has not caught up to NBTV standards

He says you should use cmos ics which is good ,but i was wondering what you would make of it as even at my lack of electronic knowledge i could see it looks a bit messy .
I have never come across a power supply like that lucky most use hes
circuit board.
I was told the reason for the 2 7905s was to isolate the analog from the
digital perhaps theres a noise problem but if its traveling via the power
rails why wouldn't it find another path .

It also requires 12V. If using AA/C/D cells, split them in two (±6V) then two low-dropout regulators...if the supplies need regulating at all. Better still, get it to run on a single +6V rail, this isn't so hard.

Well Steve when you ask they seem touchy about it and you get an answer but i would rather believe you ...why a voltage doubler chip and then regulating it to 5 volts seems pointless to me .

There's a whole load of variable/trimmer pots, indicative of poor circuit design.


I am still wondering how thats VCO 555 at the end works without a
resistor between pins 7 and 8 ...most i have seen use pin 5 as the control
input.

Good luck, if I can help I will...


Thanks Steve if you have a look at the pdfs i am using the one posted last time
and as you see there are a few slightly different versions of it .

I may as well post some pictures up of my build here see what i am up to .
Attachments
harryspowersupply.JPG
I lost voltage after the regulators so didn't use the trany rail splitter part
harryspowersupply.JPG (103.47 KiB) Viewed 3897 times
2.JPG
Using this old shf pay tv down converter case for the metal detector circuits
2.JPG (144.56 KiB) Viewed 3897 times
5.JPG
That B of a power supply and 555 transmitter and ic6 part of the circuit
5.JPG (157.04 KiB) Viewed 3897 times
6.JPG
6.JPG (192.48 KiB) Viewed 3897 times
10.JPG
second board just the VCO is not built yet
10.JPG (166.09 KiB) Viewed 3897 times
11.JPG
second board fits good !
11.JPG (157.45 KiB) Viewed 3897 times
22.JPG
The VCO built to the schematic ...but i am a bit iffy about it
22.JPG (158.89 KiB) Viewed 3897 times
33.JPG
Hooking the boards up
33.JPG (192.5 KiB) Viewed 3897 times
40.JPG
Well clock and tranys 1 and 2 work after replacing the 10k with a 100 ohm
on Q1 mmm
40.JPG (145.89 KiB) Viewed 3897 times
scope.JPG
With coil on transmitter circuit on Q3 i am told this is the correct waveform now to debug the rest of it !
scope.JPG (207.24 KiB) Viewed 3897 times
13.JPG
Next photos are of the arm idea using old crutches both types
13.JPG (200.8 KiB) Viewed 3897 times
14.JPG
bit of old pvc pipe for arm rest
14.JPG (141.06 KiB) Viewed 3897 times
19.JPG
cut out the arm rest and used a old drill handle ..
19.JPG (181.34 KiB) Viewed 3897 times
21.JPG
21.JPG (199.36 KiB) Viewed 3897 times
23.JPG
My first idea was this type of crutch but could not find them after my work it turns up ! wouldn't you know it !
23.JPG (215.98 KiB) Viewed 3897 times
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Postby Klaas Robers » Wed Jan 08, 2014 5:09 am

Harry, it looks to me that this is one of those designs that uses as many circuitry as possible, to maximize the income of the electronic shop. I cannot understand that so much electronics are needed for this simple tasks....
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Postby Harry Dalek » Wed Jan 08, 2014 7:05 pm

Klaas Robers wrote:Harry, it looks to me that this is one of those designs that uses as many circuitry as possible, to maximize the income of the electronic shop. I cannot understand that so much electronics are needed for this simple tasks....


Hi there Klaas

I got interested in making a metal detector for a bit of fun when we go to phillip island .........they have a nice beach there ,bit of coin hunting :wink:

I was going to make this design i found it very simple and elegant but asking every one told me its to simple you need a complex design ,i sort of looked into it and there is a problem with simpler metal detectors when using on Mineralized Soil....i think.

Still i don't think the DIY ones do have a Ground Balance control which lets you adjust it to the type of soil your using it on any way .

Not sure how that works /

I think how this pulse induction metal detector works it has a transmitter and a receiver i gather the transmitter sends a pulse via the coil into the ground then the clocking switches between the transmitter to the receiver
to pick up any thing, but has me wondering why the receiver ic is before the switching as wouldn't that ic get a very strong pulse all the time from that Mosfet switching after or not could not be good for the ic ?.

OH well i will plod on with it and see if i can make it work mess of a thing it is .
Attachments
matchless300bw[smallpdf.com] (1) (2).pdf
556 cmos metal detector
(858.08 KiB) Downloaded 192 times
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Harry Dalek
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Postby Steve Anderson » Thu Jan 09, 2014 5:06 pm

I'm kinda out of my knowledge base here. Correct me if I'm wrong (probably) but most metal detectors require the object to be at least partly Ferrous, containing Iron (e.g. Steel etc). Coins and the like are non-Ferrous, often Nickel, so how they work I'm not sure.

I'll have a look at the linked file and come back..

Steve A.
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Postby Harry Dalek » Thu Jan 09, 2014 6:44 pm

Steve Anderson wrote:I'm kinda out of my knowledge base here. Correct me if I'm wrong (probably) but most metal detectors require the object to be at least partly Ferrous, containing Iron (e.g. Steel etc). Coins and the like are non-Ferrous, often Nickel, so how they work I'm not sure.

I'll have a look at the linked file and come back..

Steve A.


Yes so was i and still a bit to say the least ...

On Metal detectors its like Golf and different golf clubs you just about could used a different design for different soils and or what metals your looking for ....when you are talking the high end high dollars can do it all ..the rich get richer isn't it always the way ! :evil:

OH no Steve Both ferrous and non ferrous ....i find it confusing too and again it depends on the metal detector design there must a fair few different types of metal detectors (golf clubs)
:wink:

I used to think it was like radar its using the VLF type i wanted to try first
so at ULF and VLF you can transmit right through the earth so i thought well it hits metal and bounces back. its using radio waves ?

Well when i pointed that out i was told wrong boy its the magnetic field is inducing a magnetic field in the metal object which the metal object is sending back before its tiny induced field collapses which the coil receives.

I am told i need a PVC plastic the bottom section of my metal detector shaft even the brackets and bolts should be nylon or plastic .

The coils wrapped in foil which seems to increase the magnetic field ?

I am having problems with the simple floating ground works then doesn't i think i will just use 2 9 volt batteries this split rails driving me nuts .

I have the circuit going up to ic 6 pin 6 seeing the waveform and placing a metal object near the coil i can see a reaction on my little scope ,so this is a good thing ,i might as well hook the rest of it up see what happens .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Harry Dalek
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Postby Harry Dalek » Sat Jan 11, 2014 10:59 am

Well hooking every thing up it seems to work .

There are as Steve says far to many trimmer controls a nightmare to adjust
making it hard to case up as i need to make sure i have adjusted it right before i do which is a real pain .

I am going connect the detector coil via a coax for now so i can get it away from the table which has metal so i can adjust it at a distance it doesn't detect any thing till i let it .

Oh well the hard bits over what a pain of a circuit that was .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
User avatar
Harry Dalek
"Fester! Don't do that to 'Thing'"
 
Posts: 4084
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