PICKINI - an easy to build PI detector

[F117]

hi bernard,
my board is finished :-) looks good, i think.....can you tell me, which wire gauge you use for your coils?

regards, marc

I am not a coil specialist - any standard PI coil around 300-400uH will do. Plenty of examples on the forum here.
I used 20 AWG enameled copper wire for 27 turn 20 cm coil.
best regards,
- Bernard

[Schatztaucher]

thanks:-)

[nick holas]

hi all
very interested by this MD could you adapt your hex file for an another pic like the 16f628 or 16f630 ??
a vdi can't be adapted to you metal detector (only ferrous/non ferrous display led)???
thanks for your reply.

[F117]

hi all
very interested by this MD could you adapt your hex file for an another pic like the 16f628 or 16f630 ??
a vdi can't be adapted to you metal detector (only ferrous/non ferrous display led)???
thanks for your reply.

Most Microchip microcontrollers in the 16F family with a 14 pin housing are pin compatible.
The 2 extra things to look for are (at least one) internal comparator and timer1 that can be enabled by the comparator output ("gating").
I had a quick look at the 16F630 datasheet and this seems possible.
Have a look also at the 16F1824/1825... series. They are more recent (less likely to become obsolete in the near future) , have onboard EEPROM, 32 MHz internal clock...

As for discrimination, there isn't any at the moment. You could try and sample the flyback pulse slope with the internal ADC - this is something I will implement once I have more spare time... You can see on the schematic/PCB that the analog signal is already connected both to the comparator input and an ADC input.

Best regards,
- Bernard

[nick holas]

thanks for your reply but i m noob in pic (just know putting hex in ) i ve done an lc meter and when i mesure a coil inductance , when i pass a ferrous target the inductance grow, when i pass a non ferrous target inductance reduce a little .can t this experience couldn t be used for a simple discriminative metalndetector (only ferrous/non ferrous) with 2 led display ???
sorry for my college english.

[F117]

thanks for your reply but i m noob in pic (just know putting hex in ) i ve done an lc meter and when i mesure a coil inductance , when i pass a ferrous target the inductance grow, when i pass a non ferrous target inductance reduce a little .can t this experience couldn t be used for a simple discriminative metalndetector (only ferrous/non ferrous) with 2 led display ???
sorry for my college english.

When you want to build a pic based metal detector with discrimination, go for an induction balance detector. Measure the phase shift between TX and RX + the RX amplitude. A basic PI detector has no discrimination features.

[nick holas]

thanks for all

[wheato22]

Just curious if anyone has reproduced the PICKINI design so far ?
Some feedback would be greatly appreciated.
I have built 6 detectors so far, all with 20cm coils and they all work fine...

regards,
- Bernard

Thanks Bernard,

The obvious quality of your PICKINI design and excellent online documantation makes for a compelling project to build. As a long time metal detector and general electronic hobbiest I am planning to make three PICKINI.v2 detectors as an PIC design and PI theory teaching project for me and my two grandsons. That will be me learning and then me teaching my two grandsons how to build the project. So far I have yet to decide to make the PCB's at home versus sending the Eagle file to a local PCB Fabricator. And then there is the HEX loader process I have never tried before, but that seems to be straight forward with what appears to be inexpensive USB based PIC HEX loaders available from EBay. I've wound many BFO and VLF coils in the past so the PI coil seems simple enough. Lastly, the parts list largely consists of easily located passive components ... with a few active components soldered in...... again thanks to Bernard's PIC based design. My only hitch so far is locating a supplier here in Silicon Valley for the 4.7K ohm pot and switch combo. Wow thats a first!

Thanks again Bernard, for your excellent documentation and buildable design. I too hope to begin stuffing my first board soon....

Regards,

Larry

[F117]

Hi Larry,
glad to hear that you like the project and even better: introduce your grandsons to the hobby.

My only hitch so far is locating a supplier here in Silicon Valley for the 4.7K ohm pot and switch combo.

The value of the potmeter itself is not critical. It may be 4K7 / 10K - you can replace it with separate potmeter and power switch in case it is nowhere to be found in Silicon Valley - which is hard to believe...
To program the PIC, I use the PicKit3 USB programmer
http://www.microchip.com/stellent/id...irects=pickit3

Best regards,
- Bernard

[mikejr0046]

Need help put together a pickini 2 when I turned it on I just got the welcome tone and nothing after that. Reprogrammed the 1824 many times still nothing, thought that my serial programer was not working as I just bought it at Radio shack for half price, veleman 4048 kit. I bought enough parts for two so I etched another one, measured all resisters and caps and put it together in the process I discovered that on the first one I had cut the connection between 8&9 on the pic I thought I had made a solder error. Fixed my mistake hooked a coil up turned it on and got the welcome tone,two clicks,then a constant loud tone, the pot had no change in the tone. I hooked number two up and got the same results. The coil was 27 turns 24 gauge wire 366umh,1.65 ohms unshielded at this time. I discovered by mistake if I moved the coil next to a large piece of steel under the loud tone it was picking up the metal giving a positive signal. Shielded the coil no difference. I was using a computer power supply went to an 18 volt battery pack from a drill, nothing changed. Any ideas ? Thanks Mike in snowy MN.

[F117]

Hi Mike,
Coil data looks OK - not sure about the resistance, but inductance is OK.
Make sure that the voltage at pin3 of the Opamp is 8.00V.
If you have a scope, check the signal at the comparator input = pin 9 of the PIC.
When you test it with an unshielded coil inside the house, it will pick up a lot of noise, and even when you turn on the unit and leave the potmeter to minimum sensitivity, it may have problems in getting a stable reading.
The two or three clicks you hear after the welcome tone is just a delay during which there is no comparison with a reference ( = stable reading)
Go outside away from any EMI and turn it on again.
I use 2 9V battery blocks in series to test for a short time. For longer hunting, I use 15x NiMH AA cells in series ( 3 blocks of five).

Best regards,
- Bernard

[mikejr0046]

Going outside did not help but if I touch the back of the reg and the mosfet at the same time the tone stops. It does the slow tick and if I bring a piece of steel next to the coil it sounds off with the same tone not sensitive to something small. Pin 3 is 8.000 volts. My scope has not been used for years and does not seem functional now. Why did you question the resistance of the coil ? Turning the pot does not change the ticks. Thanks Mike in MN

[F117]

but if I touch the back of the reg and the mosfet at the same time the tone stops

.
Looks like a ground problem. Is there some sort of discontinuity in the ground signal on the PCB? Opamp ground OK ?
Turning the pot only changes the number of samples that are accumulated for a valid measurement.
Also check the polarity of the 10MF coupling capacitor towards pin 2 of the opamp. When the polarity is wrong, there won't be any signal towards the opamp input - but as you have some change in tone, this is most probably correct.
Check if the damping resistor across the coil is properly soldered.
Somehow, this problem seems familiar - I had it with one board and it had to do with bad soldering, just can't remember which one.

[F117]

Please check that the signal at pins 8/9 of the microcontroller looks like this:



this is the end of the flyback decay (clipped to +/-0.6V and amplified 5000 times.

Pin 11 of the microcontroller should output a digital version of this pulse ( after the internal comparator).

At pin 13 you should have an adjustable DC between 0 and 5V (almost) with the potmeter.

Obviously, the PIC programming, timing etc is OK since you have the welcome sound and the ticks.

[mikejr0046]

Both of them act the same way. Scope not working. Pin 13 is doing 0 to 5 with the pot. All the solder joints look good under a magnifier light. Went over most of them anyway. Mike in MN