Let's made a PC-base metal detector with usb interface !!!

[Aziz]

Hi sled,

I personally do favour the least amount of work & effort (I'm lazy *LOL*), the KISS-principle and the poor man's solution. IMHO, there is really no need to develop another USB sound card. The USB sound cards these days are really nice and cheap ($5 - $50) and will satisfy the requirements.

You could setup a kickstarter project and get eventually paid for your costs (see www.kickstarter.com ) . There hasn't been any metal detector projects registered yet. You need a lot of "backers".


You could try your ideas with Netbook/Tablet/Laptop + USB sound card first before starting an embedded systems project. That would make things easy and fast. Just a so-called proof of concept.

Anyway. Your project is very interesting and I'll set it to my "watch-list".
Cheers,
Aziz

[Silver Dollar]

This thread got me fired up to use a USB sound card interface so I bought one of these to play with;

http://www.ebay.com/itm/261376624605...84.m1439.l2649

It's only 16 bit but $10.67 and a bit of room in the box to experiment. Now to find a good cheap (free!) compiler
to work with....

Oops I bought too soon this one is even cheaper ($10.07)!
http://www.ebay.com/itm/USB-6-Channe...76624605&rt=nc

[greylourie]

Nice thing about PC soundcard is that you can record stuff. And there are loads of programs for experimentation....audacity ZLCR etc etc

[sled]

This thread got me fired up to use a USB sound card interface so I bought one of these to play with;

http://www.ebay.com/itm/261376624605...84.m1439.l2649

It's only 16 bit but $10.67 and a bit of room in the box to experiment. Now to find a good cheap (free!) compiler
to work with....

Oops I bought too soon this one is even cheaper ($10.07)!
http://www.ebay.com/itm/USB-6-Channe...76624605&rt=nc

nice! you should be able to get some results even with 16bits - most sound cards accept a 1Vrms as full scale input, so you can (theoretically) measure down to 0.015mV, but in reality I'd assume that the effective number of bits you get is about 12bits, makes 0.24mV. If needed, add a low noise pre-amplifier

One important thing to mention is, that you should open your sound card and trace the output back to the chip, make sure there is some current limiting resistor in the path, a low impedance coil could short or overload the output. Most sound card work well with a load impedance of 32 ohms

I can recommend the following utilities to get started with (they are all cross-plattform so your application should work on windows/linux/osx):

- Eclipse IDE or CodeBlocks IDE (both free, cross plattform)
- Qt for the GUI
- Qwt for plotting
- Jack Audio to interface with your sound card in real time

You can either use C/C++ or Python with all the above, although I'd recommend to use C/C++.

Here are some resources:

https://github.com/jackaudio/example-clients (sample applications for jack audio, best to start with the simple_client.c example)
http://www.acoustics.hut.fi/~aqi/software/QTjackDemos/ (there's a link to the source code somewhere in the text)
http://qt-project.org/doc/qt-4.8/gettingstartedqt.html (simple Qt tutorial)

[Silver Dollar]

Thanks for the links! That JackAudio looks good!
I'm leaning towards FreeBasic as that's the language I'm most comfortable with.
It's supposed to be able to talk to C libraries so that should help. I may even
just squeeze a DSP processor into the box and ignore the USB part. There's a
lot of potential timing problems with all the layers involved.

I have some 30F4011's and 4012's around that might make for a good MD.
I'm thinking no display. The computer or a handheld terminal can do that
to set it up. Then it would be sound output only.

I probably should have bought 2. One to build into a MD and one to use
for algorithm testing on the computer.

[sled]

If you're on windows there might be a chance that you could use the ASIO interface for real time audio
I'm quite sure your sound card uses the CM6206 chipset (http://www.steila.com/USB4IO/CMedia/...asheet+1.7.pdf) they even recite the feature list 1:1 on ebay from the datasheet.

Regarding the dsPIC, it's much easier to use an audio codec that has an I2S interface that you can hook up directly to your dsPIC. The Minelab X-Terra Series uses the WM8731 audio codec with a DSP (TMS320VC5402).

There are already some shields out there with the WM8731- commercial ones and DIY ones

The commercial shields (without any processor):

http://www.mikroe.com/add-on-boards/...o-codec-proto/
http://microcontrollershop.com/produ...oducts_id=4229

An interesting DIY signal processing board with a dsPIC, inlcuding some sample code for the dsPIC:

http://ebrombaugh.studionebula.com/s..._sp/index.html

[Silver Dollar]

Hey I just found the Datasheet for that CM6206 chip. I'm pretty sure that's what's in that box.

That dsPIC board looks great! I wish he was selling bare boards it would take a bit to get one
made even with the gerber files. Maybe I can slip it in when they make some pcb's at work?

I had look at the codec sheilds at one point but went off to other things maybe one of these days...

[sled]

this might be interesting too: http://www.daqarta.com/dw_ggnn.htm

[Silver Dollar]

There's an interesting schematic on the libstock website but I think they expect you to connect several pcb's to make it.
http://www.libstock.com/projects/vie...wm8731-example

It would be nice to have a board with the dsPIC and WM8731 on it for development...

[sled]

Hi,

Another starting point is the schematic/PCB of the codec shield, it has the essential components/wiring (on Page 3): www.mikroe.com/downloads/get/1463/acodec_manual_v100.pdf

One thing that is important is to avoid the MIC IN and use the LINE-IN.

I've just DIP-ified the WM8731:

[Silver Dollar]

Funny I just got two of those 28 pin adapters to test some eproms at work and then found out
the eproms are 20 pin! So I guess I could use them for a WM chip. Where'd you get the WM?

The schematic I was referring to is this one;


I noticed the Mikroe bd uses the Mic input. What's up with that? Of course I'd use the line in's.

I have a 30F4011, with the dip adapter you could use this board to make a MD;

http://www.ebay.com/itm/271316189992...84.m1423.l2649

[sled]

I got the WM8731 from Mouser (Part# is 238-WM8731SEDS/V) they sell it for 2.44$ + shipping costs (they're based in the US). Shipping to Europe was a pain, I had to order parts for ~80$ to get "free shipping" and paid another 10$ for customs clearing by FedEx + taxes

[Altra]

Check this out. I bought one last year. Have not played with it yet

Lots of code for Auduino, like vco's, delays/echo. Open source pcb. Could be used on a Uno32 with a little jumper or two.
Or make your own motherboard. All pins have pads, so it's not like the Mikro codec board.

http://www.openmusiclabs.com/projects/codec-shield/

[sled]

Yep, I've seen that board - it's among the best as it provides "bare" access to the codec and uses the LINE-IN instead of the MIC-IN Schematic, Gerber Files can be found on the Wiki page here: http://wiki.openmusiclabs.com/wiki/AudioCodecShield

My goal is to create some kind of motherboard with an ARM Processor on it with enough juice to bridge the I2S audio over USB to the host PC (the board will pop up as external sound card, no drivers required). Then I can implement and test all the algorithms on my computer and later on port it to the ARM processor directly, power it from batteries and take it to a field test.

Another important factor is the I/O with the coils, the board will only provide some RCA connectors for the coils, nothing more. The whole pre-amp (RX) and power-amp (TX) can be developed on your own board and connects through pin headers.

[Silver Dollar]

Oh ya that is a good one. If you look in the store there you can get the bare PCB for $5 too!
http://www.openmusiclabs.com/store1/...-shield-store/

I just got an order from Mouser, their prices are cheap (even in 1 - 2's) and they have the $5 shipping option.
I think they are catering to home builders to drum up a bit more business. I priced one chip at one of the other
suppliers and it came to $15 Mouser had it for $8.

The asian companies on Ebay have a WM for $10 you can get it from Mouser for $7.44 it seems the tide is turning.

Those ARM processors can be powerful but they are like desktop processors. I got two tablets with ARM processors
one flys as it's like a quad core, the other is slow as its a dual core (I think). What language do you use on the ARM?

One thing keeping me away from the dsPIC's is that it is easiest to program them in C. I do Basic and assembler but
never fully learned C. It seems easy to make mistakes with the terseness though with a bunch of libraries available
it's probably easy to do the complex stuff like USB.