Completed Minipulse Plus Projects by Geotech members

[Qiaozhi]

#1
The first member to successfully construct a working Minipulse Plus, apart from myself and Andy (Silverdog) of course, is Dean Sarelius.

He was able to detect an Australian dollar coin similar to a euro at around 15cm. Although the coil has very little interwinding capacitance, and has a measured inductance of 300uH, he feels that he can improve on the coil design.

Here are some photos of the finished detector:

[Qiaozhi]

#2

The second member to successfully construct a working Minipulse Plus is josewashere.

Here's some info on the build from Jose:

Here are some pics of my completed minipulse plus and the coils I used with it.
I fitted a divider in the detector case so I have the pcb on the upper area and a 6.8amp 12v LiPo and speaker on the bottom section. I intend to mount the detector in a carry bag rather than attach it to the shaft / coil.
The home made coil is 355uH and 1 ohm made with multistrand teflon insulated wire. I used poly spiral wrap and shielded with mylar. Originally I relied on the black graphite coating on the inside of the housing but in trying to eliminate falsing on grass I went to using mylar around the coil. The mylar shield works better than the graphite one but with slightly reduced sensitivity. I still need to fully remove the graphite from the coil housing.
On a ring size target I get about the same distance as the Coiltek but on a can size target the Coiltek is better. Gold ring is just detectable at 12 inches (30cm) if you hold your tongue just right. Both coils can sample down to 7us


I will do some opamp changes to see if I can get any improvments

Thanks for a great project!

Jose

[Qiaozhi]

#3

The third member to successfully construct a working Minipulse Plus is joop.

Here's some info on the build:

It's the first detector in the world that can stand upside down! Great if you need to swap coils.

I have used a custom case for the electronics and spend some time isolating the battery pack from the aluminum casing. After all, the case is connected to the battery plus.

The detector stem is made of a fiberglass fishing rod, the armrest is aluminum. They are connected by PVC rods. The coil is a low capacitance zigzag wound type which I found in the Chance PI thread, it is screened with mesh braid that comes from a TV coax.

Thanks for a great project!

[Qiaozhi]

#4

The fourth member to successfully construct a working Minipulse Plus is CAS.

Here's some info on the build:

Just finished my MPP and found it a pretty straight forward build. Instructions are easy to follow and the quality of the board from Silverdog is good. Its only an experimental board so I am not going to put it all in a case but I think it would definitely benefit from sheilding. In my workshop there is lots of RF interference from fluros, lots of SMPS and various other instruments so there was quite a bit of noise on most of the test points. I am also using an unsheilded, 345uH relatively high capacitance coil and running the board from a 12v 10A power supply which doesnt help. Even so, I am pretty impressed with the air tests. With a small 3mm bolt I get about 10cm.
You will have to excuse the mess on the bench as I was making it during breaks from customers and 'real' work.

regards
Pat aka CAS

[Qiaozhi]

#5

The fifth member to successfully construct a working Minipulse Plus is Chet.

Here's some info on the build:

I have completed the Minipulse Plus (rev C) kit. I am very pleased with the the kit and the results. On the bench with all the noise from in house TVs etc. it detects a Nickel at a little more than 5" (13 cm). This is with a COILTEK 10" X 5" Mono coil. The delay time is down to approximately 7 us with this coil.
I plan to do some modifications to the pulse rate and sample periods, and possibly add a ground balance before enclosing it into a case.
I followed the build procedures which are very good. A few minor suggested changes; add to Step 3, Q2 (2N3904), R9 (10k) and R5 (20k), add to Step 7, Short PL3 again, add to Step 8, connect 50k Reject pot to PL3.

Thank you for a fine project,
Chet

[Qiaozhi]

#6

The sixth member to successfully construct a working Minipulse Plus is Treasuremole,

who found a 2 gram emerald and gold ring with the MPP at the beach.

[Qiaozhi]

#7

The seventh member to successfully construct a working Minipulse Plus is KRinAZ.

This is an MPP that has been further modified to operate in high iron mineralization of the gold bearing areas of Arizona (or Australia).

Below is an overview of the modifications made by KRinAZ to his MPP (RevC). The full discussion can be found in Forums/Projects/Minipulse Plus/Getting ready to build the MPP:
http://www.geotech1.com/forums/showt...-build-the-MPP

The coil was basically as described in the Coils Forum - under Chance PI around Posts #110 -----126

General mods to suit my operational requirements:

Speaker is 32 ohm 1 9/16" (40mm) mylar flat cone.

On/off & volume control in one added, 5k audio taper pot.

SAT speed control added by replacing R29 with (1M linear pot in series with 37K resistor).

Threshold (Audio) control changed from (1k resistors in series on either side of 220k linear pot) to (68k series resistor "low" side, 133K series resistor on "high" side, with 10k linear pot) so now the full range/rotation of the control is useful and adjustment is much finer.

Sensitivity control added by replacing R33 with (5K linear pot in series with 1K resistor).

Added MUR460 diode in series with search coil after the MOSFET to speed up the search coil flyback recovery. (Note - this is already included in the REVD layout).

Swapped U5 (NE5532) with LM4562 for better sensitivity.

For U8 & U9 use TL071/2 instead of TL061/2 for better sensitivity & noise rejection.

Timing changes to enhance detection of very low TC targets:

TX freq at 5000 pps via 50k trimmer pot (which replaced R8 [from the project spec of 1000 pps]).

TX pulse width at 30uS via 3K3 trimmer pot (which replaced R7) (from the project spec of 56uS).

Sample pulse width at 22uS via 50k trimmer pot (which replaced R11) (from the project spec of 48uS).

EFE (secondary) delay at 140uS via 33k trimmer pot (which replaced R10) (from the project spec of 160uS).

Primary sample delay adjusted to minimum of 6uS (from the project spec of 22uS).

Detection depth (air tests) also included below:

[Qiaozhi]

#8

The eighth member to successfully construct a working Minipulse Plus is Olof N,

Here is the feedback from Olof:

I´ve just finished my MPP Rev D.
The build document was quite easy to follow but the sample delay in step 6 confused me a bit at first, I didn´t understand that the main sample pulse started on the falling edge of the signal seen at TP5. But at least I´m not alone, I´ve seen others with the same problem as me.
I built a coil as seen in the Chance PI coil thread. It measures 296 uH and R1 is set at 180 Ohm. Works really great!

Next step is to let a friend of mine make a housing for the coil with his 3D-printer

Olof N

[Qiaozhi]

#9

The ninth member to successfully construct a working Minipulse Plus is pedrete,

Here is the feedback from pedrete:

Sorry for poor pictures quality.

You folks can see the solution for a PVC pipe extension of a crutch and that problematic power line with a switch between battery and connection jack.

More to say, that my new Inductance meter, recently arrived from Hamburg (there it come from China), say 1mH (1000uH) and 2.4Ohm. It have 25 turns (5x5 spider coil from this forum) of 0.5mm enameled cooper wire. The coil is 22.5cm between coil centers. ...it works good.
It is dry summer here in Europe this year and many times i´am lazy to dig so deep.

Nice kit.

[Qiaozhi]

#10

The tenth member to successfully construct a working Minipulse Plus is geoscash1,

Here is the feedback from geoscash1:

Coil tests - Detection with 7" inch round 24awg magnet wire bundle wound coil is:

US Quarter - 7"
US Nickel - 9"
14k gold wedding ring - 7"

Thanks for a great little project, much happier this time around...
Geo

A blow-by-blow account of the project build can be found here -> Rev D Build #2 Started

[Qiaozhi]

#11

The eleventh member to successfully construct a working Minipulse Plus is godigit1,

So here it is, Im calling it the Mini pulse "Magnatrol" wader.

DSCN2138.JPG

DSCN2144.JPG

Its mounted on PVC shaft with the battery pack built into the shaft.
I'm using a Whites Arm cuff and a clamp on bicycle grip for the handle.
Garrett AT water prof headphones and a TDI Dual Field coil.
The controls are magnetic, I put roller bearings on the pot's and I just keep a rare earth magnet on my scoop to adjust them.

DSCN2180.JPG

Here is the small Jewelry coil I built for it but still have some packaging to do to it.
I used a needlepoint frame for the pattern and laminated a skin on for the case that will eventually be gel-coated.

4" 3/4"x 9" Oval Basket coil!
26 awg solid tin plated copper wire.
320Uh and 3.1 ohms resistance.

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Here are some scope shots!
DSCN2187.JPGDSCN2186.JPGDSCN2185.JPGDSCN2183.JPGDSCN2184.JPG.

I've had it out for one quick test where I made a little video and two 4 plus hour hunts so far and I have to say I,m very pleased with the depth and sensitivity using the TDI coil. I kinda don't want to take it off.
So far Im hitting nickels decently at 12 inches and hitting items small enough their hard to find with my TDX pointer.

Here is the video I did its not to good I was holding my headphones to the camera and that didn't go to well, so when I actually could hear it it hit the nickel very well you just cant see the sweep. But Here it is anyway!

https://www.youtube.com/watch?v=tEb7qhybrXw

Thanks to everyone at the forum for covering things so thoroughly I hardly have to ask a question and especially to George and Carl for their great projects and devotion to the forum.

Best Regards.
Digit

[Qiaozhi]

#12

The twelfth member to successfully construct a working Minipulse Plus is LukeJ,

Here is the feedback from Luke:

This was my first detector project. I am quite happy with how it turned out !!

I have to give a lot of credit to the thoughtful craftsmen who engineered the project. Well Done.

The way the board was populated and each step was more or less confined to it's little section of the board was great. This feature also made the soldering easier I believe.

I don't have, up till now, any experience with this level of electronics projects. I do however have more than a decade of manufacturing experience. Specifically, Machining.

I'm certain these skills made the project flow with little to no problems. I also just took my time. Wanting to get it done right more than just get it done.

I would highly suggest to anyone who wishes to build a MPP that they buy the kit the first time around. Then, once you have the kit, read through each step and put all the correct parts for that step in a sandwich bag. Number the bags for each step. This way you can verify much easier that you do in fact have all the parts and they have been correctly identified before assembly. Double check each component with a multi-meter as well. I used this method. It helps quite a bit.

I used an oscilloscope that I bought used for $50. It's an older analog model. I had little experience with it as well. There were a few steps that when finished, I wasn't sure I had done it right. Turned out, each time, it was how I was operating the scope or my understanding of what the scope was trying to tell me. By the time I got to the end of KRinAz's modifications, I was pretty familiar with the oscilloscope. It was a great learning experience.

The coil is a 7.25" OD basket coil. The picture shows 30AWG that I used to proof the winding pattern. I cut that stuff off and re-wound it with 26AWG Teflon insulated silver-plated stranded wire. It's 30 turns, 2.3 OHM, 290mH. It works really well. In fact, I found a couple nuggets with it and my White's SPP a couple weeks ago !! The basket wind is covered in two layers of medical paper tape and one layer of medical cloth tape. I went ahead and shielded this one since one I had made previously was still hearing the ground too much in a spot I've been hunting. Spiral wrapping the silver plated conductive tape seemed to solve the issue and didn't have any measurable negative effects. I've used this method of shielding on several bunch wound mono coils with favorable results.

The coil housing is a one of a kind. I watched some YouTube videos and made myself a little vacuum forming box. Then I made two molds, a top and a bottom, from 1/4" MDF. The bottom mold was made such that it would have a protruding lip that would accept the top piece. It took a few tries with the plastic temps but eventually I got one of each that I could trim up and fit together. Turned out much better than I expected.

I would like to additionally thank, Reg Sniff. He is a wealth of knowledge and experience and had quite a bit to do with helping me get started in winding my first mono coil. He pointed me towards this forum and the article "Making a Fast Pulse induction Mono coil" by Joseph Rogowski. Excellent article. Thank you !!

So here it is, my homemade metal detector.

Luke

[Qiaozhi]

#13

The thirteenth member to successfully construct a working Minipulse Plus is Teleno,

Here is the feedback fromTeleno:

I'm using a MineLab compatible DD coil by DETECH with the following characteristics:

Tx coil: 580 uH, 1 Ohm. Damping: 470 Ohm.
Rx coil: 500 uH, 5.4 Ohm. Damping: 1KOhm

Modifications.

The induction balanced DD coil has a very short transient and I can sample at 6 us. This increases sensitivity to gold.
Some modifications are necessary for making the best of this coil:

- R3 (3.3 Ohm) shorted to get maximum Tx current.
- Tx pulse increased to 100us: R7 (1K2) increased to 2K2.

These changes allow the coil to peak at 1.1 A.

- Minimum sampling delay set to 6us via trim pot R6.
The coil is 18 cm x 15 cm, so the expected detection depth is about 16 cm, which matches the tests.
The PCB and power pack are crammed into a general purpose housing. The power pack has 8 x AA Ni-MH, Panasonic BK-3HCCE, 2450 mAh.

https://www.youtube.com/watch?v=r-1_EDF6T5g

[Qiaozhi]

#14

The fourteenth member to successfully construct a working Minipulse Plus is Tibuck19.

MiniPulse plus Rev-D

Electronics:
I am by no means electronic savvy. Nonetheless, following carefully all steps with very well explained build guide (thank you George) and visual reference https://www.youtube.com/watch?v=OyS8sfv0XJ0&t=302s
I was able to assemble the board and have a working Minipulse. I replaced R5 with a 5K trimpot and R8 with a 50K trimpot. I also routed the TX/RX pins to a 3-way switch for an on-board pin-pointer, that is connected to a 1K trimpot to match the main coil waveform, and prevent a noisy screech when switching from main coil to pin-pointer.
1K-volume control for the headphones.

Hardware:
Board housing and faceplate are 3D printed out of ABS. (photo3 & board)
Battery pack is also 3D printed to use 3X 18650. (photo -battpack)
Coil connectors are IP68 waterproof. (photo4)


Coils:
10-inch mono-loop coil: made with 22AWG magnetic wire, 362uH.
All parts are 3D printed and resin filled.
6-inch Spider coil, also 3D printed.
Pin-pointer: the core is from a recycled AM radio with 150 turns of 30AWG magnetic wire.
Housing is a ½ inch PVC pipe with 3D printed coil cap and wire cap, using a old telephone wire to connect to the board via an IP68 connector.

[Qiaozhi]

#15

The fifteenth member to successfully construct a working Minipulse Plus is hecbom.

I did the KRinAz mods and my unit runs great. I am using a Miner John's 6" coil and the sensitivity is almost as good as my friends TDI SL!