My New Pi Metal Detector (ATTiny 25)

[smity]

Something conceptually similar is already appeared on this forum:

http://174.132.129.189/%7Emoreland/forums/attachment.php?attachmentid=7989&d=1236810600

In this version whit front-end preamp (badly needed), good coil etc may be useful info. Good luck whit this project.

Tell me, who built the BT-1? Respond brothers! Interested in results, and difficulties in the manufacture ...

[taliesin]

PCB obviously the way to go when you're design's perfected, but have you ever tried "carving" one with a hobby knife to get the benefits early on?

I take double sided FR4 and trace out "lands" for parts then cut narrow strip channels to isolate them. Make two parallel scores about 1mm apart, lift the copper with the blade then grab with tweezers and pull up to remove. It usually comes away like magic! Drill through lands to link to the back side (ground plane) and then surface mount parts on the lands. DIP packages can have legs splayed out (or DIP sockets) and proper SM or leaded components can be added at will. I find this a great way to knock up simple(ish) circuits for development while retaining low-impedance ground and switching paths.

Attached Photo shows Mosfet and driver front-end for rapid test and development on a carved PCB as described. 0.1" header goes off the bottom edge on to breadboard for more circuitry in groups of two or three for easy carving

i like to use a bur ball bit in a dremmel

[AdrianM]

How easy is it to follow a line with that taliesin? I wish I'd bought a real Dremmel rather than a cheaper clone - the bearings and motor are so noisy!

[jon-ecm]

How easy is it to follow a line with that taliesin? I wish I'd bought a real Dremmel rather than a cheaper clone - the bearings and motor are so noisy!

For larger stuff I had no trouble but when it comes to putting a trace between, for example a dip socket, I had trouble following the line closely enough.

If your not setup for toner transfer or it's a fairly simple board, I'd give it a try, otherwise buy a laser printer and do toner transfer (It's all in the right paper and a hot enough iron)

I'm working on getting pcb's made for this.

[AdrianM]

I haven't tried the direct toner transfer method - I always use pre-sensitised copper clad boards, inkjet transparencies and a UV exposure unit. With this I can make boards for 0.5mm pitch LQFP's - but the price of laminate and ink-jet cartridges is getting ridiculous. I'm doubting that toner would give enough resolution although it would be a cheaper and quicker way to do it.

[bernte_one]

i use "pnp blue" transfer film in connection with an easy laser printer

[Götz von Berlichingen]

Did you add the usual decoupling Capacitors to the ATTINYs yet ?
I suggest 100nF between VCC and GND, very close to each IC.
It should make the Circuit more stable. Try and see, it cant hurt.
Your bigger Elkos are no replacement for these,
because Microcontrollers make switching Noise in the MHz Range.
http://en.wikipedia.org/wiki/Decoupling_capacitor

[jon-ecm]

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**

Your bigger Elkos are no replacement for these,

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

[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

[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

[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

[golfnut]

how do you select the comparator level?

steve

[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

[6666]

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

[6666]

Received my chips, now waiting for burner
also

the tx pulses at around 100khz to 500hz