My New Pi Metal Detector (ATTiny 25)

[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?

[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

[bernte_one]

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

[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.

[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]

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!

[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

[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 ...

[mehdi]

Hi joa-ecm
thanks for reply, surely this is my next project.

all the best
mehdi

[jon-ecm]

@mario
Currently the adc is only used for measuring the voltage divider that controls sensitivity.
noise is still an issue with it though so I make sure it returns 20 consecutive readings of the same value before changing the sensitivity threshold.


@mehdi
I don't have an inductance meter but when testing with a 8" coil wrapped out 50' of 28 guage wire single strand teflon insulated.
I can hit a penny at 8",
a 0.8 gram lead pellot at over an inch.

[mehdi]

I put up a list of components on my site here

Hi jon-ecm
good job
what is the detection depth for your detector?

all the best
mehdi

[mario]

Thanks for getting back to me!
...
If we pick it up as voltage we have alot more sources of noise,
A. amplification (not necessary on a time based solution)
B. delay time (inaccuracy in the delay time produces noise)
C. ADC Noise, Error and Resolution (if applicable)
D. Noise (Lots more noise)


I purchased the LT1016, I'll see how it dose for an external comparator, it will connect to the coil with the same bi-directional diodes and compare it with a variable reference voltage (equivalent to delay time on a conventional unit)


Thanks guys!

I'm not sure about the A->D conversion using Attinys, but with my atmegas, for proper conversion, Aref pin requires a .1uF Cap to grnd and Avcc requires a filter using a 10uH choke for noise reduction. I don't see these two pins on the Attinys?

ADC is really awesome with the @megas. Most have 10 bit resolution (although 8 bit is appropriate for most applications IMHO)!

The best way ( I have found) internal noise is to poll a persistent ADCH value to lcd.

uint16_t adc_value =0;
adc_value = ADCH;
printf("%d", adc_value);

You need 8bit mode lcd though, and I dont' think attinys have enough pins. When noisy, that adc_value is unsteady...

In other words, from my limited experience with ADC, you're probably right about your noise issues

[jon-ecm]

BT1

There are some differences,
First of all his uses the attiny12, this chip is has a max timer speed of 1.2mhz (.83 us) to get around that he decided to use the cpu to delay a predefined amount of time and then test to see if the comparator output is high or low, the max cpu speed is 8mhz (.125us) and the cpu is from my experience, horrible at counting time precisely.
mine uses a pll clock that is set at 64mhz (16ns) so it obviously will detect a smaller change in decay time

the front-end amp is a great idea though and I have plans to implement it into the next version!
also plan to convert the front-end to moistly analog and looking at the possibility of multiple comparators, less noise and simple disc.

[Tepco]

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.

[jon-ecm]

components

I put up a list of components on my site here