picoDetector

[6666]

This may not be the right place for this post

Here is a nice "little" project for people who like pics

called the picoDetector and it works

http://www.micro-examples.com/public/microex-navig/doc/076-picodetector.html

[kt315]

for ivconic - IT IS NOT MINE, PLEASE DO NOT BE ABUSE ME NOW!







http://vrtp.ru/screenshots/2448_MetFM.zip

[6666]

1250uH
thats a big coil

[Eddy71]

Not big coil - about 80 turns copper wire 0,2mm on 70mm circle.

[PaullyG]

http://vrtp.ru/screenshots/2448_MetFM.zip

I have a few 12F PICs floating around and am tempted to do a little experimenting with this for a simple pinpointer that I can just throw on a strip of proto board. So if anyone is able to post the source for this one, I'd appreciate it greatly.

Going off this topic on on md4u.ru it seems the last revision is 0.5f and is linked to here

I need to be registered to download from what I can gather and google translate wasn't much help with the registration form.

[Eddy71]

[PaullyG]

Thanks Eddy71, for the source and the project.

[Qiaozhi]

I have a few 12F PICs floating around and am tempted to do a little experimenting with this for a simple pinpointer that I can just throw on a strip of proto board. So if anyone is able to post the source for this one, I'd appreciate it greatly.

Going off this topic on on md4u.ru it seems the last revision is 0.5f and is linked to here

I need to be registered to download from what I can gather and google translate wasn't much help with the registration form.

If you examine the datasheet for the PIC16F629 and the PIC16F675, you will see that the common functions associated with pin 6 are GP1 and CIN. Likewise, for pin 5 they are GP2, TOCK1, INT and COUT.
The most likely candidates for this application are the comparator input (CIN) and output (COUT). So it appears that the comparator is being used as an LC oscillator. As metal approaches the coil it causes the inductance to change, thus altering the oscillator frequency.
I would not expect this design to be very sensitive, but please keep us informed of your results.

[PaullyG]

If you examine the datasheet for the PIC16F629 and the PIC16F675, you will see that the common functions associated with pin 6 are GP1 and CIN. Likewise, for pin 5 they are GP2, TOCK1, INT and COUT.
The most likely candidates for this application are the comparator input (CIN) and output (COUT). So it appears that the comparator is being used as an LC oscillator. As metal approaches the coil it causes the inductance to change, thus altering the oscillator frequency.
I would not expect this design to be very sensitive, but please keep us informed of your results.

12f675 is most likely what I'll be using, if I remember correctly what's in my parts bin. I don't expect I'll be putting it together for a little while, but I'll come back and dig up this post when I have and make some general comments. I'm not really going in expecting a lot out of it but with the low parts count there's not too much to be lost in having a play.

[Tepco]

I built this thing some time ago (675 PIC) for pinpointer, and it works quite well. Only important thing is that coil +2 caps must resonate @ 18.5kHz (as i remember), this is the "mid" value expected by software, so different coils and cap's within some reasonable range will work. Exactly as stated, something like 7cm for coin whit 7cm coil.
I tried whit larger coils, range is about 1/3 of "normal" detector, best that this FM type devices can do. You need to shield the coil, and use high quality caps for C6 & C7. After some warmup time, zeroed whit S1, stability is quite good. Nice, low part count, low consumption, and physically very small pinpointer. Add transistor output if you use magnetic transducer instead piezo.And this little toy have discrimination! Have a fun whit it, PCB is not needed...

[Stefano]

MalishFM

Hello,
I've built this nice pinpointer just one week ago. Despite the author said he didn't test it with a ferrite coil, I made it that way.
It seemed to perform quite well with rather good sensitivity on the bench, but once the I arranged everything in a suitable box, it turned out as completely unstable.
It was something more similar to an electronic compass instead of a pinpointer...
I tried with both shielded and unshielded coil, but it was the same.
Just before give up with it, I've decided to try also with a coil wound on a 8 mm plastic rod, so something that could go inside the plastic pipe used as probe.
Well, the sensitivity is of course much worse, probably little less than 1 inch for a standard coin on the probe top, but now the circuit is very stable.
Discrimination seemed to work well with the ferrite coil, but now with the new coil isn't that good: iron is often detected as "colored" metal.
Not tried to make a medium size coil like Eddy suggested because I had already made a box for it in the standard pinpointer probe fashion, but I'm quite optimistic that detection depth could be much better than mine.

Stefano

[Tepco]

Same thing happened to me. Entire assembly, not only coil, must be shielded like battle tank (graphite or something) to minimize capacitive effects, FM stuff is very sensitive to it. I never tried ferrite core, but whit normal coil discrimination problem exists, as expected. Magnetic, but highly conductive objects (bottle caps, steel tools etc) will exert two different effects on the coil, one is increasing inductivity (and lowering frequency) due to magnetic properties, and another is decreasing it due to conductivity (acting like short ckt. winding in the coil). So most junk, except ferrite and very rusted iron will be accepted as colored metal unfortunately. And, yes, in presence of even slightly mineralized ground, this will act more like compass, not pinpointer. Fate of FM detectors...