My New Pi Metal Detector (ATTiny 25)

[jon-ecm]

Ok, Confirmed I used a different adc input on my board, It should be no issue as I can fix it in software. That would explain why the pot isn't changing the pulse and why the pulse is different on the second chip. I will fix the hex on the website this afternoon if all goes well. I am on vacation right now so I have no way to test but I will do my best to get it right, If you use avr-gcc I can send you the c code if you want to play with it.

[6666]

Hi Jon
thanks for the offer,
would be interesting to have a look at to see if I can learn anything
from the code.

I burnt another attiny25
this one has a positive going pulse
.5ms wide and about 2ms between pulses
the pot has no effect.

the first tiny25 had a positive going pulse 4 milliseconds wide and about 16 milliseconds between the pulses, the pot had no effect.

I only burnt the flash and fuses on both chips all seemed to verify.

For the moment if you can post your latest hex that would be very helpfull
thanks
cheers

[Vermeer111]

hallo jonecm please can you post the newest details incl.the newest hexfile from you wonderfull tpimd detector here or on your site i think many people waiting for this update thank you grettings from the harz montains

[its]

posting sources would be handy if you can email me a copy it would for me be very nice..

i came across this design on the web and its nice to see some others on a forum to
share ideas and experiences with

many thanks for your work so far and keep it up
i can help making schematics and pcb design if needed

[jon-ecm]

If the voltage is changing properly on that pin it's probably a software issue and I will be more than happy to fix it for you, also that hex code on the website is pretty outdated, In later versions I fixed it so the TX would be on for only twice the off time which seemed to work better although it put more drain on the batteries.

If you know how to program in c I would be happy to share the code with you

[6666]

I tried burning my first ATtiny25 with Jons code for the TX.
and it seems to have worked, sort of.

I used a simple Bascom parallel port burner , its the same as the Dontronics DT006 burner
and the software was AVR-Burn-o-mat which is a GUI for Avrdude.

The Hex and fuses all verified, so I am happy about that .

The result was a positive going pulse 4 milliseconds wide and about 16 milliseconds between the pulses, but by varying the pot which goes to pin 2 does not alter the frequency of the pulses, so got to figure that out.

[jon-ecm]

It has manual GB but right now the presence of a target is indicated in a tone frequency difference not sound level which has advantages and disadvantages.
I had good success with using a pwm dac and sending the capacitor averaged output to a VU meter. the only disadvantage being that the meter would bob up and down if it was not held still.

Basically I've run out of resources on this chip. As it stands now I have been able to hit a nickle at over a foot with a 8" coil in 50% black sand but the lack of proper sound modulation leaves it more of a noisy hybrid pin-pointer.

This is what has caused me to move to the XPI platform. This new board uses a 16 bit ADC and averages 12 samples taken during the flyback period as well as providing the capability of varying TX length and TX Voltage. Although these features will not be available in anything I release due to patents. The source-code (c) will be made available to encourage development / modification (Although patents must be kept in mind when doing so) at your own risk.


Jon

P.S.
Out of date info on XPI here

http://www.miymd.com/index.php/projects/xpi/

[mario]

Hi jon-ecm,

did you get the ground balancing working on your unit?

[6666]

Received my chips, now waiting for burner
also

the tx pulses at around 100khz to 500hz

[6666]

Hey all
just heard from Jon
ATTINY25-20PU is the right chip to get

[6666]

Hi Jon
great project
on your website you have a video
that shows the decay wave form and reference,
where on your schematic did you have the cro connected
might have to learn about these avrs
which is the correct ATtiny 25 to order ?
ATTINY25-20PU ATTINY25V-10PU

thanks

[golfnut]

how do you select the comparator level?

steve

[der_fisherman]

Timing on your metal detector

You need someone here who knows the "timing" needed for a PI detector to give you some tips. My guess is that is the only thing holding you back.
Basically, the better a metal allows current to flow (gold is very good for example), the shorter and quicker the Rx pulse back is.....and therefore the more difficult to catch.
Maybe you should consider adding eventually the VDI circuit to tell you which metal has been detected, though not all designs can use it......
I must add that I have not built a PI for many years, nor have I built the VDI circuit either, so both suggestions may not be valid.......but there are so many here with up to date knowledge, I am sure they will help you further...
I am sure its a timing /adjustment problem only as obviously your basic design works great on some metals already, but not all.
Its refreshing to see that such a small digital design has such obvious good value, well done.
Regards
Andy

[Vermeer111]

Have anyone build this detector an can say about the "specs" from this (Detecting Deep 1 Euro, and so ) have anyon modified the Program for the chip (Diskrimination, reading with a PC ) and can i run this detector with a Big coil 0,5 m 1m thank you

[simonbaker]

Thanks for the info!
I'll add it to the pcb I'm working.

On my current pref board (mess of solder) for testing I do have a several hundred uf cap about 1" away from the chip but you know how pref boards are... **sigh**



I always thought that when it came to noise reduction bigger was always better. Is that wrong?

It depends on the frequency of the noise. For power supply ripple (usually low freq), the big ones are good, but usually only needed at the power supply. Sometimes you have a high current component like a speaker amplifier that would create voltage fluctuations on the supply "rails", and so a big capacitor across it can help reduce audio frequency cross-talk on the supply "rails". IC chips often create current/voltage spikes, very high frequency transients as they use power, and can affect each other. Big caps I believe have significant inductance and don't soak up these really fast spikes, so the tiny caps do better there.

-SB