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

[MartyJ1963]

Hi all,,,,yes, it was a bit of a headache getting it sorted, but I'm glad I perservered with it, I learnt quite a lot of new things too. Apparently not all the Mplab versions automatically update firmware. I found that out searching the net for answers and most of the problems I saw all related to the Pickit 3;- original Microchip make and the Pickit 3 clone. Mplab is supposed to load the firmware and install it for you but some versions don't. I installed about 6 different versions of Mplab before finding this out. Here is the forum page I found this information on- https://www.microchip.com/forums/m808413.aspx. I followed this to finally get it to work for me. Also, the software notified me that my target board needed 4.5v and not the normal 5v,,once I set the it to 4.5v, ticked the box and load the hex file, I pressed 'Program' and it erased the chip and programmed it with no more problems. I've ordered some more chips now to try my hand at some other projects. Hopefully my next venture with PICS and programming should go a little more smoothly,,lol. It was very kind of everyone to help me a long the way as well,,,much appreciated. Thanks. Marty

[F117]

Some pictures of a 1 hour beach hunt with Pickini v4 last Saturday, just before the game of Belgium against Tunesia:






Some old coins, a lot of tent pegs and a ww2 shell case.
Bottle caps, pull tabs,...
Unfortunately no golden earrings this time.

[MartyJ1963]

Hi everyone,,,,I finally got around to my first ever go at 'Metal detecting'! I've been building the available projects here on Geotech for about 2 years,,,and bought a T2,,,and never been Detecting until Thursday 27th, 2018. My partner and I booked a coach trip to Whitby for the day and I took along several detectors I'd built to see how they performed. The detectors I took were Minipulse Rev-E/Minipulse Rev-D/Surf PI 1.2/Barracuda/Felezjoo and the Pickini 4. I got to try them all out except the Felezjoo which will have to wait until next time now,,,not enough hours in the day!! They all performed great and I was really chuffed with having built them myself too,,apart from the Minipulse Rev-D of which Andy (Silverdog) kindly repaired for me (Cheers Andy). I'll not pipe on too much about the other detectors with it being the Pickini 4 thread but I was really amazed with the performances of all of them. Firstly, the coils I used were homemade 3DSS Coils. The elliptical coil:- 12" x 9",,320uh@3.0R,,The round coil:-11",,340uh@3.0R. I didn't find many things (limited time) or anything exciting, but finally getting to go detecting for me was exciting enough,,lol. I found a 1p coin with the Rev-D,, a 1p coin with the Surf,,the remnants of a telescopic 'Selfie' stickwith the Barracuda,,a beer cap and a boat nail with the Pickini. The beer cap was an amazing 14 inches under the sand and the boat nail was about 10 inches deep. I've got a few things to check on my Pikini like the sensitivy po,,I dont know which way round I soldered the pot but Bernard has quite kindly guided in checking this amongst other things. I can't remember off hand without my notes but the 1p coins were 12+ inches deep in the sand and I found the selfie stick in a diagonal standing position at 10 inches. I can't get to go detecting again now until the 27th of July,, in which I'll be able to try all my PI's more thoroughly because I've booked my mates caravan for 3 nights on the East coast In Aldborough,,,he's warned me though to be careful on the beach there because the military used to hold training there and they have controlled explosions there every month,,,,,Can't wait to do it again,,,Thanks again to everyone on geotech cos' theres so much more to learn (and build,,lol). Thanks Bernard for a great little detector,,I'm in the midst of building my partner one now. Regards Marty

[waltr]

Great report Marty.
These detectors do work in other places than the beach.

[MartyJ1963]

Thanks Waltr,,,,,I've got a few homemade VLF's to test out as well,,,my mate and I have finally got some farmland permission in July but he can only give us a 2 week window because he's planting again. It'll give me time though to test my T2 and home built VLF's out and see how they perform. Regards . Marty

[dbanner]

Great report Marty.
These detectors do work in other places than the beach.

Sure, if you don't mind digging every piece of scrap iron. Or if you're out in the middle of the desert.

[waltr]

I do dig every piece of iron. Four times after removing the iron there was an old coin still in the hole.
Also, I have found several pieces of iron that are 1700's table ware and other old interesting items.

Today's hunt yielded 59 iron pieces but also pewter spoon, iron fork, 4 old shot shell heads, an ornate brass something and a 1903 Barber quarter.
35 iron items are square nails. This was a very good hunt.

[dbanner]

I do dig every piece of iron. Four times after removing the iron there was an old coin still in the hole.
Also, I have found several pieces of iron that are 1700's table ware and other old interesting items.

Today's hunt yielded 59 iron pieces but also pewter spoon, iron fork, 4 old shot shell heads, an ornate brass something and a 1903 Barber quarter.
35 iron items are square nails. This was a very good hunt.

Wow, didn't realize it could be that productive.
I tried my pulse machine one time and it was almost useless. Every little piece of anything iron from tiny rusty nails to wires to whatever else. I found couple of old coins and a spoon!
From there on, I always use VLf discrim.
I guess it depends on the field one is hunting.

[dbanner]

The 35 nails you mentioned represents 35 holes dug. My back wouldn't last that long.
The non ferrous objects you found may have as well been found with a discriminator.
But the nicest thing about pulse machine is that it doesn't leave much behind.

[Rick]

Good Morning Guys,
I've built on perfboard a pickini V4, it detects a 2 euro coin at about 11cm in free air with the sensitivity set to maximum.
As damping resistor I use five resistor 100 ohm (1W) in series for a total of 500 ohm 5W. The coil is 25cm diameter, 500uH and shielded with aluminium tape.
I've measured the DC offset bias and is 11.38V with a Voltage supply of 12.55V is it correct?
I've also attached the wave coming out from the op-amp because I don't know if it's correctly dumped



Picture:https://ibb.co/nyJb0K

Could anyone helps me? It's my first metal detector

Thank you so much Riccardo

[MartyJ1963]

Hi Rick,,,,The best person to ask your questions to is F117 (Bernard) who actually designed the Pickini 4,,,he's a great guy and I'm sure he wil give you all the help you need as he's helped me plenty with the 2 x Pickini 4's that I've built. Did you build the Pickini 4 to the specifications that Bernard provided for this project? I followed the whole build from Bernards webpage, IE:- I etched the original board, I used 1% resistors, all components were to Bernards spec's etc, and I have 2 x perfectly working Pickini's (Thanks again Bernard). I think your coils inductance is bit too high though at 500uh,,,I use 300uh 3dss Monocoils with both my detectors and they both detect a 1 Euro at 14 " Inch with the sensitivity up about 80%. Also, I didn't add any other parts in my build (5 x 100 ohm resistors??). If you build a 3dss coil around 300uh I'm sure you will have better results and you'll find you won't need to shield the coil either,,,I've never had any problems with interference etc using a 3dss. But of course, the man to ask would be Bernard. All the best for a successful build. Marty

[Rick]

Hi Marty,
thank you for your response. I've built the Pickini as close as the original I was able to but I hat to use some different components:
I've used a OPA1612 because I cannot find the LM318, the 2n7000 and the BC547 and I've used 5 100ohm resistor instead of two 1K in parallel so that should not be a problem I think. The Coil I've built is from the instructions on the Pickini web page, could you please tell me what is a 3dss coil and how to wind it?
I've also seen the voltage table and instead of 6.8V as DC offset I get 11.5V and that should be a problem but I don't know how to fix it

Thank you

Riccardo

[MartyJ1963]

Hiya Rick,,,,I think the two 1k resistors are to do with the Audio section of the detector because I remember others asking Bernard how to raise the volume of the speaker and I think he replied to them telling them to lower the value of these two resistors,,,I know it's somewhere on this thread. The 3dss coil takes quite a while to make as you will need a lot of patience to wind it, but it has the advantage of not needing to add a 'shield',,,I don't know fully how the 'Self shielding' works but I think it has to do with the Geometry of the coil. Basically, you decide what size coil you would like, eg:- 10" Diameter,,,then you cut out a circle of 10" diameter from material such as 'Lexan' or stiff plastic (I use 1/8" thick MDF board) etc,,,You then measure from the outside of the circle 'inwards' about 1 and 3/4" inch and draw another circle. You then divide the outer circle's circumference into 37 segments or increments and 37 segments on th 'Inner' circle's circumference. There is a thread on how to wind the wire on this kind of form in the Coils section of the forum,,look for 'Chance' coil,,,or 'Racetrack' coil,,,but there is quite a lot of information available on the 3dss coil on Geotech. I only use 3dss coils now on all my PI's because they are really fast and don't need the tedious job of shielding etc,,,I'll see if I can find out what I have on them for you and I'll post them for you to download. I would send F117 a private message about trouble you're having with the DC offset,,I'm sure he won't mind helping you cos' he's a great guy. Here's two PDF files with some templates to give you an idea. I'll see what else I can find for you. Marty

[Rick]

Thank you so much for the help Marty!
I'll download and try to build this kind of coil, I have some MDF but after using it as a support I can leave it or I have to remove it from the complete coil?
Wich diameter and number of turns you suggest me to use?
Thank you again for the help!

[F117]

The 2 x 1K in parallel over the coil is the damping resistor of 500 ohms. There are 2 resistors of 1K in parallel to reduce the dissipation per resistor. If you use 5X100 ohms in series this should give the same result.
You should be able to detect a 2 euro coin at 25-30cm with an 8 to 10 inch coil.
The differences will probably relate to the different opamp you used.
LM318 is quite common and should be easily obtainable ?
BC547 is also very common and is used to set the DC level of the amplified flyback signal.

What is the 2N7000 ?

The wave form you are showing is not correct. Probably because you did not use the opamp that was designed in.
It should look more like this: