Someone build this, and tell how well it works.

[Elie]

http://www.electroniq.net/other-proj...r-circuit.html

[dfbowers]

http://www.electroniq.net/other-proj...r-circuit.html

Looks like it could make a very compact pin pointer if it works..

[Elie]

The coil can be made by winding 140 turns of 18 gauge (AWG) around a 6 inch form, but the coil is not used with a core.

[chemelec]

It goes Down in Frequency for Ferrous metals and Up in Frequency for Non-Ferrous.

Works OK, but Not greatly Sensitive.
A Coil wound on a Ferrite Pot Core will give a Narrower Detection Field.

[Elie]

It goes Down in Frequency for Ferrous metals and Up in Frequency for Non-Ferrous.

Works OK, but Not greatly Sensitive.
A Coil wound on a Ferrite Pot Core will give a Narrower Detection Field.

Thanks!
I neglected to add that the coil which I specified (I got the specifications from another metal detector circuit) does not have a core, but the coil specified in the schematic for this circuit does. What kind of coil did you use? Can you post a picture of the detector?

[chemelec]

Thanks!
I neglected to add that the coil which I specified (I got the specifications from another metal detector circuit) does not have a core, but the coil specified in the schematic for this circuit does. What kind of coil did you use? Can you post a picture of the detector?

Sorry No Picture.
I Just Breadboarded it, to test it out, than took it apart.
And I made 2 different coils, that I Quickly wound just for testing it.

I Didn't actually make a Ferrite Core one, But I could do one up and do some further testing.

[dfbowers]

Thanks!
I neglected to add that the coil which I specified (I got the specifications from another metal detector circuit) does not have a core, but the coil specified in the schematic for this circuit does. What kind of coil did you use? Can you post a picture of the detector?

I breadboarded one as well. It works. I used a straight ferrite slug though. It had a range of about 1" for coins and rings.

[Elie]

What I am wondering is what the range would be for a 6 inch or bigger coil. Also, I found the original circuit, and the power supply is 6-12 volts, and the speaker is 8 ohms.

[Pepe LeMiau]

I'll test it later today, I have a 24cm (around 9,5") and 16cm (6,2") coils which should be close to 10mH. These are leftovers from my experiments with Hartley's oscillator in the CM 2TRDX.
I hightly doubt that it will work any better with larger coils.

The oscillator in CM 2TRDX basically works the same way, any metal object near the coil changes the frequency of the tone, because the TX coil is a part of the oscillator LC circuit (and the 2TRDX's receiver is just an audio amplifier).
From the tests I made earlier it looks like larger coils are more sensitive only to larger objects. While a 3" coil reacted with audible changes of frequency for reasonably small objects (like coin size), 9.5" coil just ignored these. I bet there was a frequency change, but nothing I could hear.

I'll repeat the test with 555 generator just because of curiosity, I'll try it anyway because I'm looking for a simple pinpointer. Any ideas on how to "guess" the winding inductance on 10mm ferrite core ? I've read somewhere about calculating the coil without any core and then adding 20-30%, is it good enough ?

[Pepe LeMiau]

I've tried it, it's even worse than I expected.
With ferrite core coil, 1050 turns at 8mm core I got the base frequency at around 800Hz.
It reacts very well to medium and large targets, for ferrous metals the frequency goes down to around 200-300Hz at close range. However, the detection range is very poor, a couple of inches at most.
For non ferrous metals it's even worse, forget about coins and other small object because the detection range is almost non existent.

The second coil has 3 layers of 60 turns, 180 turns in total at diameter 160mm. Doesn't react at all to small objects even if they're thrown inside.

And I thought I'll have a nice, simple pinpointer
Perhaps this thing could be useful for locating metal structures in walls, but that's all.

[Elie]

Thanks for checking that out. I do not know how to figure the inductance difference for a coil with a core, but someone here must.