My Pulse Oscillation detector project.

[WM6]

Hi Teemo. Congratulations on this inventive design.

On your web site you say: "There is no discrimination between metals."

But this is basicaly intermitent BFO, and BFOs are able to distinguish between Ferro and NonFerro (by changin oscillator frequency Up or Down). This is very interesting potential of your design in comparison to equal PI uC solutions. Why you would not take this very interesting advantage / potential of your design?

Expecting your next firmware with Ferro NonFerro distinguish capability.

[Teemo]

Hello everybody.

I got feedback from Andy who has built the project from my website.
He has made the video about testing it.
With his permission I share the link for the video :http://xyolater.bplaced.de/?Videos:Metalldetektor

Best regards,
Teemo

[Teemo]

Hi

No replays, and no feedback to the computer connection topic. I guess it got too messy. Nobody wants to hook up so many wires.

So now I release new version firmware (1.26). This makes the circuit adapting even better to various coils and mosfets. Now it has automatic adjustment of the comparator reference voltage. When connecting power supply the PIC automatically adjusts the voltage treshold level for comparator.

I add new firmware as attachment to here also.
And picture of PCBs on my table:


Best regards.

[Teemo]

Connecting to PC

Hello everybody!

I have made new special firmware for my project. This time it is for connecting the circuit to computer.
Link to the page:http://digiwood.ee/en/metal-detector...ter-connection
I also attach connection schematic and firmware directly to here.PO_metaldetector125.zip

[Teemo]

Hi Teemo,
So far I have uploaded hex to the pic.(my programmer finally arrived..xmas delay?)
I have also etched and drilled the pcb drawn by APberg.
Still collecting parts.
Having a few problems with a 7.5mm spacing for C1 etc in that value.
I can find 'greencaps'.
For a proto..would they be suitable?
Also I noticed on your site, a comment about the coil specs.
I have mainly home wound coils to suit surf p.i. etc
around 400uh.
I see you recommend changing C1 value. above 110uh
Can you advise what parameters for C1 value to suit different coil uh's?
Or maybe in software .
Cheers
John

Hi,
I have multiple mounting holes for C1 in my PCB layout, to mount 10mm, 15mm, or 20 lead spacing.
Of cource you can try using 'greencaps' but make sure that the voltage rating is at least higher than mosfet's. 250V rating maybe. But the stability with greencaps may be not good, there may be drifting as the capacitor warms up, so when testing give it couple of minutes to stabilize.
About the coil inductance, the bigger inductance is not actually problem if coil resistance is higher also. I have not specified the coil resistance values yet. But I guess I must compile a table of coil incductance, resistance and C1 values.
About my recommendation about changing C1 value to larger I changed my mind-- use the same value capacitor as cpecified. I will try to update my website about that also. I have found out that running the circuit at lower frequency decreaces its sensitivity to smaller objects. Frequency depends only on coil inductance and C1 capacitance. So when coil is larger inductance already then to increase C1 shifts frequency down even more, and that is not good.
Only potential problem with higher inductance is that the energy stored in coil during coil charging pulse may go too high, and then resulting flyback voltage may go too high. Anyway nothing bad happens even then, mosfet will not burn, it will only work in the avalance, and dump the exess voltage. You may notice mosfet getting hot then.
So John, if you already have coils, do not be afraid to connect those to the circuit and try out how they work.

Teemo

[johnandles]

Hi John,
There is nothing special about programming the hex. You may experiment with the parameters in asm file if you wish to tune: the sensitivity and compref(comparator reference voltage).
Looking forward to hear how you are doing.

Hi Teemo,
So far I have uploaded hex to the pic.(my programmer finally arrived..xmas delay?)
I have also etched and drilled the pcb drawn by APberg.
Still collecting parts.
Having a few problems with a 7.5mm spacing for C1 etc in that value.
I can find 'greencaps'.
For a proto..would they be suitable?
Also I noticed on your site, a comment about the coil specs.
I have mainly home wound coils to suit surf p.i. etc
around 400uh.
I see you recommend changing C1 value. above 110uh
Can you advise what parameters for C1 value to suit different coil uh's?
Or maybe in software .
Cheers
John

[Teemo]

Hi John,
There is nothing special about programming the hex. You may experiment with the parameters in asm file if you wish to tune: the sensitivity and compref(comparator reference voltage).
Looking forward to hear how you are doing.

[johnandles]

looking forward to build this project.
Just waiting for my programmer to arrive.
I have the Pic12f...
Anything I should be aware of about programming the Hex ?
Cheers
John

[Teemo]

Hello.
I made some tests today to see how my circuit works with different capacitors for C1. I just got some new Wima MKP4 47nF 630V- polypropylene capacitors today.
And it turns our that differences are HUGE. Oscillation lasts much longer with good quality capacitor. With polyester (MKT) capacitor (47nF 400V), not sure what brand, I had first the circuit detected about 64 oscillations before the oscillation decays under the treshold. But with the new WIMA cap it detects 96 oscillations. So it really matters. And the decay value (t_result in assembler program) is twice with WIMA, than it was with the other cap. Frequency did not change much.

So it is essential to have a good capacitor for C1.

But also this was too good, for the circuit to work, because oscillation from the last pulse is not decayed yet when the new pulse is coming on. So with too good C1 and low resistance coil circuit may not work at all.

Teemo

[Teemo]

Thanks for pointing out, I corrected the link now. Sorry, about that.

Happy holidays,
Teemo

[joop]

Hi Teemo,

I noticed an error on your website, the link on your firmware page called metaldetector110.asm is pointing to the file metaldetector100.asm

[ApBerg]

Hello Teemo

Nice! a update from the software, next week hope to test it. The led I used is a low current one, I think only some 2mA..
Well see if I have an other fet.....from the IFR730 I have plenty, so it is a first to use in experiments..

Best regards

Ap

[Teemo]

Hello
I made new experimental version of firmware code, asm and hex available: http://digiwood.ee/en/metal-detector/firmware-page
It now uses frequency information also. Much less reaction to the ferrite.

AP, your current consumption is so small that, it is a miracle it works. 20mA, Only the LED takes half of that, and other half goes to the microcontroller and coil. This new version code might not work with that mosfet.

All the best,
Teemo

[Teemo]

Hello Teemo,

Yes the current is only some 20mA..I like that, with your fet how high is then the current ?
The detected ferrite is giving more sound when it is removed from the coil, can it be that I have the wrong working freq.?

Found that the circuit can use many coils.. it works at many different one's. The last I used (on the photo) has a ferrite in it, by shifting that ferrite different uH 's can be made ,the circuit alway's works..

It is a nice circuit and if it can reject the ferrite,( ground effect) it is a good pinpointer, again thank for sharing !

I have not much testing done, the room were my scope stands is not heated...

Best regards,

Ap

Thanks Ap,
With my mosfet K2134 average current draw is about 64mA.

[ApBerg]

IRF730 may not to be the best MOSFET for the job. According to the datasheet it needs pretty high gate to source voltage. So it is probably limiting current.

Hello Teemo,

Yes the current is only some 20mA..I like that, with your fet how high is then the current ?
The detected ferrite is giving more sound when it is removed from the coil, can it be that I have the wrong working freq.?

Found that the circuit can use many coils.. it works at many different one's. The last I used (on the photo) has a ferrite in it, by shifting that ferrite different uH 's can be made ,the circuit alway's works..

It is a nice circuit and if it can reject the ferrite,( ground effect) it is a good pinpointer, again thank for sharing !

I have not much testing done, the room were my scope stands is not heated...

Best regards,

Ap