PICKINI V3 - an easy to build PI detector

[bernte_one]

can it give Problems to connect a 5v piezo buzzer for Audio without the pre-resistor 2K2?

build the next v3 pickini with spiral flat coil and get good 5cm on 0,4gr Nugget in air
measured all parts before soldering for best tolerance
maybe this Weekend it find out the correct damping value for my coil

what i can say from my experience with pickini
coils with low L coils will not work good (Surf pi range 250-320µH)
coils with heavy copper shield will also not work good (Mirage pi coil)

pickini works best with simple monoloop of yv wire or litz wire (over400µH) and bigger Diameter 35-45cm for good depth
for example 50-60cm in air for small copper pcb 100*60mm with 45cm monoloop coil, tested indoor

and with flat spiral coil of litz wire for good Gold hunting (max 20cm Diameter) very sharp pinpointing at middle of the spiral

good luck for all

[BC547]

Dabbo,
the pulse you are seeing is the amplified flyback pulse of the coil when switching it off.
This has nothing to do with the hex file.
There is something wrong around the front end stage: mosfet, diode voltage limiters or polarity of the coupling capacitor. Check the components and traces around the opamp.
Also the virtual ground = the second opamp that provides half of the power supply as virtual ground voltage.
When you get the welcome sound, your PIC microcontroller is programmed correctly.

Adjustment of the trim potmeter may be dependent on the battery voltage: apply the optimal voltage = 12V and readjust .

[Dabbo]

good morning to all, today i tested my pickini v3. i still have the same problem. target sensitivity is very low. gold ring 9 gr at 15 cm. i think that square pulse is too brief ... 10 microseconds approximately. when i put a target near to the coil, flyback current changes in oscilloscope but audio tone begins tardively. i think that the curve is not correctly analyzed in my pcb. the square wave in pin 3 of pic, that i see in pickini v3 internet site is 50 microseconds. it is possible that file hex is corrupted? thanks to all. greetings dabbo.

[Dabbo]

yesterday i had a supply of 12,4 volt. I measured 5,8 volt on pin 3 of pic 12F1840. i dont reach 5,3 volt turning trimpot. thanks to all dabbo

[bernte_one]

@Dabbo
the trimpot on pcb has how much Volts at your pcb?
(as i remind my best results are with nearly 5,3V)

[BC547]

Dabbo,
what is your supply voltage ?

Optimal performance is with 12V.

[Dabbo]

[Dabbo]

i mounted a second pickini v3 pcb and i think it's ok. i utilized the pickini v2 coil but the recognition distance is lesser respect to pickini v2. gold ring of 9 gr at 6 cm.....respect to 35 cm of v2. I record on pic Pin 3 a square wave of 10 microseconds of duration. the square wave must be longer? Thanks to all, regards dabbo.

[BC547]

Bernte_one,
Thanks for clarifying this with a diagram.

The connections to the potmeter are exactly like you describe.
The green wire in your diagram is the +5V, the blue one is the potmeter wiper [ 0 .... 5V ] and the red wire is the ground connection.
Have a look also at the picture at the bottom of this page:

http://users.telenet.be/willaert/MD/pickini/pickini_en/V3/electronics.html

Here, I used a red wire for the 12V, another red for the 5V to the potmeter, orange for the wiper and green for ground.

[Dabbo]

Thanks bernte-one. I make another pickini v3. in this way probably I will find the trouble. thank to all. regards dabbo.

[bernte_one]

i think Bernard means this way

[Dabbo]

i have the welcome sound and the search sound but l78l05 is too hot. i use 12 volt battery but pickini response is battery discharged. tomorrow i will check the pcb lines. tankyou very much. dabbo

[BC547]

A couple of remarks at first sight:

1/ You only have 2 connections to the sensitivity potentiometer. The missing one is ground. The potmeter is just a voltage divider between 5V and GND. Connect the free pin of the potmeter to ground. This connection is the same as the battery minus.

2/ Battery connection is OK. But for a 9V battery ? The optimal supply voltage is 12V.

3/ Maybe a short circuit at the copper side ? Do you get the welcome sound when switching the board on ?

- Bernard

[Dabbo]

[Dabbo]