PICKINI V4 - an easy to build, self adjusting PI detector

[BC547]

Hi Nick,
Yes, the sensitivity potmeter is needed to supply a DC voltage 0...5V at the sensitivity ADC input.
I use a 4K7 linear potmeter combined with on/off switch.

Enjoy,
- Bernard

[nick holas]

Hi Bernard
Very good job you ve done.
I m going to build one for m'y wife
I cant sée the sensitivity potmeter value .is it the same than v2,v3?
Thank you.

[BC547]

Pictures of the 2 Pickini v4 builds I tested throughout last winter up to now:





The pushbutton for pinpointing is located at the top of the handle.
The coil shells are intended for an induction balanced coil. Here I use a monoloop coil in the outer circle.
Batteries = 3X LiIon 16350 3.7V are in series - placed inside the upper part of the aluminum stem ( from cheap walking stick ).

Have fun,
- Bernard

[BC547]

Hello Bernard! Is it possible to work in the non-motion mode for prolonged times?
This will enable operation with larger coil (frame coil).

Yes, there is a connector for a pushbutton that switches from motion (connection open) to non-motion (connection closed - intended for pinpointing by hovering over the target).
When you connect a switch instead of a momentary push button, the detector will remain in motion or non-motion.

- Bernard

[eclipse]

Hello Bernard! Is it possible to work in the non-motion mode for prolonged times?
This will enable operation with larger coil (frame coil).

[BC547]

what's the depth you're getting on a 1 euro coin on the beach (dry sand) and for what the diameter of the coil?
- is the detector usable in wet salty sand?
- can it see gold objects like rings or chains?

- 1 euro coin: 20-30 cm depending on coil diameter, ...
- any PI detector is usable in wet salty sand, also this one
- it can detect gold objects

[Teleno]

Hi Bernard. You project is very interesting. Some questions:

- what's the depth you're getting on a 1 euro coin on the beach (dry sand) and for what the diameter of the coil?
- is the detector usable in wet salty sand?
- can it see gold objects like rings or chains?

[BC547]

[BC547]

Pickini V4 is the 4th evolution of the Pickini Pulse Induction detector based on pulse width measurement aka temporal sampling.

Pickini V1 and V2:
http://users.telenet.be/willaert/MD/..._en/intro.html

Pickini V3:
http://users.telenet.be/willaert/MD/.../V3/intro.html

Pickini V4:

http://users.telenet.be/willaert/MD/pickini/pickini_en/V4/intro.html

The major advantage of the Pickini V1 and V2 design over the V3 version is the fact that the former 2 have a stabilized 12V power supply, while the V3 is powered directly from the raw battery supply.
When the V3 version is powered on, there is a calibration cycle that will set up the internal slicing level to measure the pulse width.
As power supply of the battery gradually drops, the internal setup gets less efficient, reducing the overall sensitivity of the V3 detector.
That is why I decided to redesign the V3 completely, including an automated setup for both the DC level of the amplified flyback pulse and the DC slicing level of the internal comparator.
This requires 2 adjustable voltages: one is the DAC output of the PIC controller and the other is a filtered PWM output with high resolution.
The Pickini design is a Pulse Induction detector based on temporal sampling.
This principle is described in the book "Inside the metal detector" on page 170 = PI design 5.
Unlike voltage sampling, the width of the flyback pulse is measured.
It has the same pitfalls as the voltage sampled detector, but then in the time domain: the closer we slice the flyback puls to the steady state return value, the more sensitive the device will be.
The major problem with this is, when sampled too close or higher than the steady state voltage, the detector will become instable.
The same rule is valid for the voltage sampled detector: the closer the sample is taken after the flyback pulse, the more sensitive.
When the sample is however taken too soon, the flyback voltage is still in the transient slope and readings will become unstable.
With Pickini V4, both the DC offset of the amplifying opamp and the DC slicing level are tuned to each other. The result is a very sensitive detector that is calibrated taking into account the battery raw power supply and coil differences.This calibration is done only once at startup, and takes about 20 seconds.
When searching for an extended period of time, it is useful to repeat this sequence by switching the detector off and back on again. This will guarantee optimal sensitivity when the battery voltage starts to drop.

Other features that were already in V1-V3:

- joyful welcome sound- continuous 1Hz Geiger tick to signal live activity
- low battery sound- coil error sound = no flyback pulse detected. Usefull mostly when first powering the board. Forgot to connect the coil, coil is shorted, bad MOSFET, ...
- sensitivity adjustment potmeter - combined with on/off switch. This will adjust the amount of samples that are accumulated for each reading. Cranking up the sensitivity is in reality only possible in a very deserted place with no radio interferences whatsoever. As opposed to trying to crank up the sensitivity indoors next to a wifi access point...
- pinpoint button, that switches the detector behavior from motion to non-motion, allowing the lucky treasure hunter to hover over the target before digging massive holes.

The PCB size is about the same size of Pickini V1/2.
The entire description can be found here:
http://users.telenet.be/willaert/MD/pickini/pickini_en/V4/intro.html

I have so far built 2 complete detectors based on V4, field tested them for over a year now and I am quite pleased with them.

Take the detector outside, hold the coil in the air - away from noise, switch it on and wait for about 20s for the calibration to finish.
After that, you should have a very sensitive PI detector.

Enjoy,
- Bernard