Matchless metal detector

[nick_f]

Hi Guys,

I played with a Matchless metal detector circuit, designed by Rev Thomas Scarborough.
I modified a few things and it started working better. It is far away from the performance of Hammerhead, but I bet it works better than some other metal detector projects.
I uploaded a (poor quality) video on youtube, you can have a look at it here: http://www.youtube.com/watch?v=tBdBsYcVlS4
I hope that soon I will upload a better quality video, plus the modified diagram.
The coils are not built according to the specifications, I grabbed two CRT coils that rotate the image (the small round coils close to the neck of the CRT tube). They have approx 14.5mH, while the original design would use something like 1.5mH.


Regards,
Nicolae

[WM6]

Congratulation Nick.
I build one in past with max depth 5cm (2") on coin in soil.
Waiting on your mod schematic.

[nick_f]

Congratulation Nick.
I build one in past with max depth 5cm (2") on coin in soil.
Waiting on your mod schematic.

Hi WM6. Here is the new diagram. Not much was changed, but the operation improved significantly. My conclusion is that the original design could have not worked too well with a transistor with high amplification factor (such as BC549C). Having a potentiometer between base and emiter allows a better adjustment of the voltage in the colector of the transistor, which should be around half the power supply voltage. Unfortunately the power supply has to be stabilized, otherwise the detector will require readjustment very frequently. I suppose there can be a few more improvements added to the diagram, such as an R-C group in the emiter of the transistor (maybe a 1kohm resistor and a 10uF tantalum capacitor) and the pot should be lower value, surrounded by some resistors. Maybe I will do some more testing later.

I uploaded a new video for the Matchless detector on youtube. I better give you the channel, because I might delete it again later. http://www.youtube.com/user/nick1f

Regards,
Nicolae

[mikebg]

Nicolae, for more sensitivity you need more amplification of RX signal, ie instead transistor you should use an opamp.

For the present try attached transistor circuit with better stability of operating point relative to threshold of comparator. When battery voltage changes, it will maintain better collector voltage as half of supply voltage.

You can also increase TX power. For this purpose you should use NE556 instead ICM7556 and should reduce resistance connected in series with TX coil.

[taliesin]

hi Nicolae,
nice video .it works well.i don't know if it's my computer or what.but i couldn't hear too good the volume is very low for me anyhow.nice component boxes in the background byt the way.i will have to invest in some.
tal

[nick_f]

Nicolae, for more sensitivity you need more amplification of RX signal, ie instead transistor you should use an opamp.

For the present try attached transistor circuit with better stability of operating point relative to threshold of comparator. When battery voltage changes, it will maintain better collector voltage as half of supply voltage.

You can also increase TX power. For this purpose you should use NE556 instead ICM7556 and should reduce resistance connected in series with TX coil.

Hi Mike,thanks for feedback. I initially tried the circuit the same way you have drawn it. But you will soon see the insane value of the base resistor required to bring the voltage to approx Vcc/2 (which is over 30 Megohm!). I have done a Spice simulation and although the voltage on colector still varies.

You can see how by adding the resistor betwen base and emiter, the base resistors have decent values and also it seems the voltage on colector is more stable than in the first case.

I also simulated the circuit with a RC group in emiter. Even if it does not seem to be as stable as image 2, I think it will improve the behaviour when temperature variations appear.


Regards,
Nicolae

[nick_f]

hi Nicolae,
nice video .it works well.i don't know if it's my computer or what.but i couldn't hear too good the volume is very low for me anyhow.nice component boxes in the background byt the way.i will have to invest in some.
tal

Hi Tal,
Thanks for feedback. I noticed the sound is a bit low, but it was working fine for me (using a pair of headphones). When I use active speakers, the level can be adjusted to a higher degree. At the moment I don't know how to adjust the sound volume, I only started doing videos. In the next videos, I will try to correct this issue.

Regards,
Nicolae

[WM6]

Another project from Thomas Scaraborough. Coil can be DD or OO type ( RLA can be replaced by buzzer):

[solomon]

I need link for Complete Details

am sorry
I need link for Complete Details and tested to work for Metal Detecting depth like one meeter
or half for gold or metal

v. thanks

[wallker]

Another project from Thomas Scaraborough. Coil can be DD or OO type ( RLA can be replaced by buzzer):

Jel moze neki pdf sa ovim projektom.
Pozdrav.

[Qiaozhi]

Jel moze neki pdf sa ovim projektom.
Pozdrav.

Please make your posts in English.
http://www.geotech1.com/forums/showthread.php?t=10526

[Carl-NC]

I see the Rev Scarborough has a new design in the latest EPE.

[WM6]

Jel moze neki pdf sa ovim projektom.
Pozdrav.

Here you can find original "Matchless MD" project in different resolution and colour presentation.

Ovde mozes naci originalni projekat u razlicitim resolucijama i bojama prezentacije:

http://www.geotech1.com/cgi-bin/pages/common/index.pl?page=metdet&file=/projects/matchless/index.dat

[der_fisherman]

I see the Rev Scarborough has a new design in the latest EPE.

Can you post it for us here?
Thanks
Andy

[maikl]

At this link free download "Everyday Practical Electronics March 2012" http://www.pdfmagazines.org/magazine...arch-2012.html there is the latest design of the Rev Scarborough (55 str.)... called "LRC Beat Balance Metal Detector"...