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

[Aziz]

Hi Simonbaker,

quite awful wiring on the back side. But there is some order. It is not optimal but does the job at the moment. Digital control lines are made with thin magnet wire (solderable).
Aziz

[Aziz]

Hi friends,

I am getting into trouble. I need more than 15 I/O lines. I would like to have some more user interface lines for experimenting. Using external crystal oscillator does not make sense to get an additional I/O line. The external oscillator consumes 15 mA at 5 V. The ATtiny2313 itself needs 20 mA at 5V for full speed. So why not use two of ATtiny2313? And I will have more I/O lines than really needed and can extend the platform with some more user interface. I don't want to use the ATmega (16 MHz clock). I would like to have a minimum 20 MHz clock. And the ATtiny2313 is really cheap and easily available than a particular ATmega type.

There will be two of ATtiny2313's:
One for user interface (master)
One for PI control (slave).

A two-wire mode operation costs only total 2 I/O lines on each micro. One of the micro could provide the clocking for the other one. The user interface could run independently from the PI control (real multi-tasking/multi-processing).

The digital power supply delivers sufficient current for two micros. Due to the more flexibility, there can be realized more different and very interesting operating modes.

Aziz

[simonbaker]

Hi Simonbaker,

quite awful wiring on the back side. But there is some order. It is not optimal but does the job at the moment. Digital control lines are made with thin magnet wire (solderable).
Aziz

Thanks Aziz -- it is good, shows me what can be done.

Another question: when you use the magnet wire, do you need to strip the enamel with a knife or something, or does the heat melt and expose the copper for the joint?

Regards,

-SB

[Aziz]

Hi Simonbaker,

Thanks Aziz -- it is good, shows me what can be done.

Another question: when you use the magnet wire, do you need to strip the enamel with a knife or something, or does the heat melt and expose the copper for the joint?

Regards,

-SB

the enamel is melting during soldering. The wire is destined for this purpose. So it isn't a common magnet wire. But makes the digital wiring fast.

Aziz

[simonbaker]

Hi Simonbaker,



the enamel is melting during soldering. The wire is destined for this purpose. So it isn't a common magnet wire. But makes the digital wiring fast.

Aziz

Thanks Aziz. I would like to get some wire like that. Is there a specific name or brand?

Regards,

-SB

[Götz von Berlichingen]

I use Magnet Wire, too. It was advertised as "solderable".
Well, my old simple Iron was too cold to solder it,
so i had to buy a (cheap) Soldering Station that goes up to 450 C.

[simonbaker]

I use Magnet Wire, too. It was advertised as "solderable".
Well, my old simple Iron was too cold to solder it,
so i had to buy a (cheap) Soldering Station that goes up to 450 C.

Interesting, I'll experiment with my magnet wire, see what happens.

Regards,

-SB

[Aziz]

Hi all,

I did not tell you yet about the control signaling from the PI board to the laptop software. The signaling is necessary to tell the laptop software, what is going on with the PI board and what the software should do. Any user interface events have to be signaled to the laptop software and the software will react on this. This is a pure remote control interface to the software (audio interface).

A DTMF coding (dual-tone multi-frequency) will be used for this (very likely). So any user interface events will be overlayed to the modulator output going to the sound card. To produce less noise, the signalling will be switched on on action only. The software will "detect" DTMF coding automatically (GB button, pin-pointing, mode changes, calibration, ...).

The DTMF coding uses a quite low frequency range from 697 to 1633 Hz. It will not overlap with the modulator frequency (much higher). 4 bits can be coded by one trasmission pulse. Successive codes must be transferred for more information (DTMF protocol).

This step will be done very very late. Once the laptop software is started, no more adjustments should be made on the laptop (software could be put in autostart). The laptop can be put into the backpack for operation (it also runs with closed display). This is the only way, which makes the usage of this laptop detector reasonable. The mode settings will be loaded automatically from the hard disk (configuration file).

It seems to be complex but it isn't.

Aziz

[Aziz]

Hi all,

I had an excursion into coil modelling again (PI coils). It will take some time and is quite interesting. This project will be delayed for a while.
No, not really. I am focusing to convenient and high performance PI coil for this project. See GoldProspectinginOz forum.

Aziz

[Aziz]

Hi all,

it seems, we have found an impressive improvement for bigger PI mono coils. Bigger coils suffer from the sensitivity to small targets while the bigger targets were detected on large distances pretty well.

From the point of magnetic field simulation results, we can combine the advantages of both different sized coils. The improvement will even outperform equal sized mono coil. This improvement will have a good response both to small targets and to long distance targets.

Just working on magnetic field simulations, which take quite long time to calculate.


Aziz

[Aziz]

Hi all,

I am not happy with selection of micro controller yet. I need a digital communication interface to the PC not to overload the analog interface with further noise. I am thinking of using either RS232 or USB-1.1. The latter one can be realized with software and less hardware overhead (two zener diodes and some resistors ).
Look at:
http://www.obdev.at/products/avrusb/index.html
http://www.xs4all.nl/~dicks/avr/usbtiny/
http://www.harbaum.org/till/i2c_tiny_usb/index.shtml

A bi-directional digital communication would be very very fine and flexible to the design. It makes some features possible (auto calibration, loading of timings and other parameters, bi-directional user interface and much more).

I will very likely not use the ATtiny2313 anymore. Probably the ATmega16 would be much more flexible and convenient (more I/O lines and memory). It could also support a basic stand alone version (without laptop).

I will think of how to go on. Not decided yet.
Aziz

[Aziz]

Hi all,

I have found the convenient micro controller: the ATmega16 is a good choice enabling the most flexible system design with low power consumption (almost as cheap as ATmega8, ~6 EUR). Firmware updates could also be done easily. I will use the asynchronous RS232 interface for the communication, as the application does not demand any high-speed data exchange possibilities. It also makes the software coding very easy.
I think the 16kB program memory is big enough for the whole application. If not, the ATmega32 could be used (pin-compatible) with minor changes in the firmware.

The laptop needs an additional USB port for the RS232 interface (USB <-> RS232 converter). So the total number of USB ports for the application will be at least two:
- external 24-bit USB HD sound-card
- RS232 converter
- GPS module (optional)

I will start with the microprocessor module next week. I have a sample of ATmega16 and ATmega32 already at home. Also the MAX232 line driver for the RS232 interface.

Aziz

[Götz von Berlichingen]

I wonder where you buy your ICs, Reichelt sells a ATmega 16-16 for 2.20 Euros.
Only free Samples are cheaper, i never tried this at Atmel.

[Aziz]

Hi Götz,

I wonder where you buy your ICs, Reichelt sells a ATmega 16-16 for 2.20 Euros.
Only free Samples are cheaper, i never tried this at Atmel.

Thanks! That was a really good idea.
I have bought my last AVR micros from Conrad. You know, Conrad is a bit expensive.

I see, the ATMEGA 644-20 PU is also available there (20 MHz and pin-compatible!). I will prefer the 20 MHz variant, if I can get them. Otherwise the 16 MHz ATmega16/ATmega32.

Regards und mit freundlichen Grüssen,

Aziz

[Aziz]

Hi all,

the mentioned DTMF encoder and decoder will not be implemented anymore. It is obsolete now. But the algorithm for the DTMF decoder is quite attractive to speed the whole channel decoding up. It is much faster than the FFT algorithm and decodes only on one frequency, whereas the FFT for the whole spectrum calculates. The algorithm is called Goertzel algorithm (seeWikipedia). The multiple harmonics must be decoded each individually. They all will be faster than the FFT calculation and the block size need not to be power of two. This will make the laptop software faster and save more battery.

Aziz