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Offline GeremiaTopic starter
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« on: April 29, 2014, 07:05:29 am »
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Hi all,

i'm on the way of learning some metal detecting basics, i'm not good in electronic, so i took a power mosfet, 2 diodes, an opamp and hooked to an ARM board.
The concept is simple, scan a standard wave then loop-scan and point out the differences.
Basically i ended up having a metal detector + oscilloscope in one device, i can observe the decay curve difference of each material like i've read in some papers out here, and also observe my coil resonance to find out the right damping resistor value.
It's a sparetime project in early stage, i just want to show my practical implementation of pulse induction discrimination using more sw and less hw.

<a href="http://www.youtube.com/watch?v=y0eIjSEB31Y" target="_blank">http://www.youtube.com/watch?v=y0eIjSEB31Y</a>

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Offline 6666
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« Reply #1 on: April 30, 2014, 01:33:09 am »
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Wow thats a great looking project, well done,

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Offline Mudflap
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« Reply #2 on: April 30, 2014, 07:49:43 pm »
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Do you think the ARM will be able to provide a fast enough response? Will it be able to handle the switching and analysis?

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Offline GeremiaTopic starter
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« Reply #3 on: May 01, 2014, 09:52:43 am »
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Well, it depends on how much math to apply, but at first i need a less noisy and faster flyback current decay. Timings for triggering the mosfet and sampling seems not an issue.
Can someone suggest me a [cheap]commercial PI coil to use? I saw minelab commander mono and dd coils for SD/GP/GPX could be candidates, i just don't know the specs of the commander dd coil, i mean, should i use one coil for tx and the other for rx (are them equal or different?!?!) or bridge them in parallel (!?!?!?) like i saw in this pinout?
{alt}

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« Reply #4 on: May 09, 2014, 04:06:28 pm »
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Hi Geremia

I did not see your video yet as I need to get a plugin first. Any ways just wanted to tell you that for discrimination on a PI detector it is much better to use two coils one RX and the other TX. You do not need to buy a fancy coil for your project and by the way I'm working on a similar project too. You need to build your detector round your coil and not the other way round so make a coil the way that you would think it to be right for example 0.8mm copper wire 240mm diameter coil and 24 turns for the TX and 0.5mm copper wire 120mm diameter coil with 40 turns for the RX

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Posted on: May 09, 2014, 10:16:37 pm
OK well got the plugin and saw your clip, I must say that it's quite interesting are you using a DSPIC ?

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Offline GeremiaTopic starter
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« Reply #5 on: May 13, 2014, 06:50:46 am »
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Hi,

thanks for the coils tips, but i already bought 2 minelab commander coils, one DD and one mono, hoping to have less issue to take care of, hoping these are simple coils without addictional passive components.
I'm using an STM32

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« Reply #6 on: May 13, 2014, 09:17:40 am »
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Hi Geremia,

looks promising. Can you share your circuit diagramm, and maybe some parts of the code.
I got my first Arduino Uno last weekend, and first made an BFO shield.

I need some advice for programm the arduino to interact with a pi  circuit or at least measure the incoming signals.

I know the arduino is not fast enough for a super pi, but it has good voltage sensitiviti.

which you much succes

thanks

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I CAN MAKE PCBs FOR YOUR DIY PROJECT  offer only within EU

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« Reply #7 on: May 14, 2014, 04:15:39 pm »
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Hi Geremia
.
Do keep us updated with your progress that you have made and possibly some more video clips.

Regards

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So many questions so little time

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« Reply #8 on: May 14, 2014, 06:19:27 pm »
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Hi Garemia,

I find that 390µH to 400µh coil values work right. Dampening resistances of 500 to 600 ohms. Use a scope to be sure, unless you have a few hundred mosfets laying around. Pulse repetition rates of 100 to 400 Hz with 4% duty cycle pulse. I like 160 Hz with 250µS pulse width. If you want the same sensitivity of your primary coil, then use the same values for your secondary, only make the secondary smaller, so that you can detect small and large targets with the same sensitivity.

golddustcarl

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A bad day at gold prospecting or metal detecting is better than a good day at work.


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« Reply #9 on: May 16, 2014, 07:23:58 am »
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No big progress so far, i need to build a new pcb with less noise with separate TX/RX coil, as you can see actually it's quite spartan :Smiley
The minelab monocoil does not like to be damped, most because i'm not expert in electronics. In most schematics there is a damping resistor around 500ohms, then there is another resistor in series with the 2diodes, sometime around 500ohms too, some times 2,2K, some other 30k ?!?!?! I think i should play accurately with this second resistor.

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