Question about frequency counting metal detectors

[Mr Eastwood]

hi, i read an article on "All About Circuits" where someone had built a crude detector using an Arduino by counting the coil osc. frequency, is this method ever used in commercial detectors?

As i understand the Colpitts osc. feeds the freq counter to the Arduino, and then it basically just compares the delta count of the coil osc. (with metal present) with a (no metal present) baseline count and, if there is a difference, it flags as metal detection.

Article here..
https://www.allaboutcircuits.com/pro...-with-arduino/

thanks in advance.

[BC547]

I don't think a reference oscillator is needed.
Just count the number of periods during a fixed interval.
Store these values through a running average array and detect anomalies = target presence.

[Mr Eastwood]

I don't think a reference oscillator is needed.

the count reference is just the osc. in the microcontroller counting the coil osc.

[waltr]

As described in that "All About Circuits" article this is basically a BFO type metal detector.
The only BFO MD's that might still be made and sold would be toys.

They have been superseded since they are not as sensitive nor can they discriminate metal types.
Very neat idea using a microprocessor to measuring the No metal frequency then when the frequency changes indicate metal detection.
Probably not a great detector but a good learning project.

[Mr Eastwood]

thanks waltr

well, i did a bit of BFO googlin and just found and read Carl's excellent paper on BFO. http://www.geotech1.com/pages/metdet...theory/bfo.pdf

The reason i asked was i'm currently just enjoying playing around with the microcontroller BFO idea as a first MD project, and i'm just curious as to how sensitive I can make it.

[Carl-NC]

A good way to get started. Have fun!

[kt315]

interesting but not new in our world. this is KOSCHEY-FM detector. http://www.metdet.ru/FM.htm
http://www.metdet.ru/CC.zip
Chtchedrine A., Kolokolov Y. Frequency meter metal detector// CIRCUIT CELLAR. 2001, N130.

[kt315]

[Mr Eastwood]

interesting but not new in our world. this is KOSCHEY-FM detector. http://www.metdet.ru/FM.htm
http://www.metdet.ru/CC.zip
Chtchedrine A., Kolokolov Y. Frequency meter metal detector// CIRCUIT CELLAR. 2001, N130.

extremely helpful thanks! I was really quite disappointed with the range of the one in the article, even with the 0.1uS sampling time it was using which is close to my PIC based design. I think even if you went to town on it you'd not get much back for your effort.
I think my next project will be a PI design.

[kt315]

also you can look p/p MALYSH FM of Eddy71. http://www.geotech1.com/forums/showt...2150-Malysh-FM