Metal detector
Archiver
Posts: 46,084
Greetings all,
I'm interested in designs for a metal detector that can be read
by a BS2. A recent issue of Circuit Cellar (May I think) had an article
by two Russians that appears to have lost something in the translation.
The web sites listed aren't much help unless you can read Russian.
This design uses a 555 timer as an oscillator and measures the
change in average pulse width as opposed to changes in frequency. The
example formulas used are confusing as different variables appear to be
used in the text when showing examples. It looks like an interesting
idea. I'd like to read more about this approach, can anyone give us some
comments or point us to some additional references.
Thanks, Theron Wierenga
I'm interested in designs for a metal detector that can be read
by a BS2. A recent issue of Circuit Cellar (May I think) had an article
by two Russians that appears to have lost something in the translation.
The web sites listed aren't much help unless you can read Russian.
This design uses a 555 timer as an oscillator and measures the
change in average pulse width as opposed to changes in frequency. The
example formulas used are confusing as different variables appear to be
used in the text when showing examples. It looks like an interesting
idea. I'd like to read more about this approach, can anyone give us some
comments or point us to some additional references.
Thanks, Theron Wierenga
Comments
Leroy
Theron Wierenga wrote:
>
> Greetings all,
>
> I'm interested in designs for a metal detector that can be read
> by a BS2. A recent issue of Circuit Cellar (May I think) had an article
> by two Russians that appears to have lost something in the translation.
> The web sites listed aren't much help unless you can read Russian.
>
> This design uses a 555 timer as an oscillator and measures the
> change in average pulse width as opposed to changes in frequency. The
> example formulas used are confusing as different variables appear to be
> used in the text when showing examples. It looks like an interesting
> idea. I'd like to read more about this approach, can anyone give us some
> comments or point us to some additional references.
>
> Thanks, Theron Wierenga
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
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Web address is skif.net/~ykol
This is for one of the Russian authors.
Regards, Theron
I read the CCI article with great interest as well. I'm especially
interested in the matched filter algorithm, which I don't understand (yet).
The author's assertion that beat-frequency metal detectors inherently
suffer from poor sensitivity is false. Adequate stability and isolation
between oscillators is not achieved without effort, but many commercially
successful single-loop metal detectors have been designed this way and
continue to give excellent service.
Two multiple-loop design approaches are also popular:
[noparse][[/noparse]1] Induction Balance, where two co-axial transmit loops are fed out of
phase, causing total signal cancellation in a third receive loop located
between the transmit loops. Nearby metallic objects upset the balance,
yielding a sharp increase in signal output from the receive loop.
[noparse][[/noparse]2] Transmit/Receive, where a single transmit loop is oriented at right
angles to the receive loop, causing total signal cancellation unless nearby
objects warp the magnetic field. The two loops may be widely separated,
giving increased ground penetration capability.
It is generally possible to distinguish iron from other metals by measuring
relative frequency or phase of detector output. This information came from
an old library book whose identification I've unfortunately lost (all I can
tell for sure is that chapter five contains the relevant details). There
are many simple metal detector designs in electronic circuit cookbooks...
> I'm interested in designs for a metal detector that can be read
>by a BS2. A recent issue of Circuit Cellar (May I think) had an article
>by two Russians that appears to have lost something in the translation.
>The web sites listed aren't much help unless you can read Russian.
>
> This design uses a 555 timer as an oscillator and measures the
>change in average pulse width as opposed to changes in frequency. The
>example formulas used are confusing as different variables appear to be
>used in the text when showing examples. It looks like an interesting
>idea. I'd like to read more about this approach, can anyone give us some
>comments or point us to some additional references.
Mike Hardwick, for Decade Engineering -- <http://www.decadenet.com>
Manufacturer of the famous BOB-II Serial Video Text Display Module!
as a controller? Looks like it would be plenty fast enough.
Jon