Replies to Minipulse Plus

[Qiaozhi]

I just finished my copy of MPP.
Switched it ON and it is working... awfully !
It is acting opposite; when i close up any metal to coil : audio fades !?
Audio is chatty and dirty, lot of "weh-wah".
Coil is 300uH.
Voltages are alright.
I tried to adjust Reject Sample Delay with trimmer and pot, all possible positions, no good results.
All components are checked and good.
I only haven't put brand new J113 there, had 2 old from a scrap and used them.
But those seems to be alright too.
I haven't exactly followed whole this topic and read all the posts, is there any already posted video with good working MPP?
Anybody made video? Anybody posted it?

Did you carefully follow the instructions in the Build Document? ->

---------------------------------------------------------------------------------------------------------------------
If you go through the following steps carefully, and in order, you will have a greater chance of
ending up with a detector that actually works. Do not proceed to the next step until you have solved
any problems encountered in the current step. If you get stuck at any stage during the build, then
seek help in the Geotech forums before moving on. Do not simply populate the whole board;
discover it doesn't work (which will be the most likely result) and then post in the forums: “I've
built the Minipulse Plus, and it's not working. What's wrong?”, as you will receive little sympathy
from other Geotech members.
To reiterate:
Please follow the instructions step-by-step.
---------------------------------------------------------------------------------------------------------------------

I suspect you've been a bad boy and populated the whole board before testing. If so, I would suggest reading each step now, and follow the test procedure. This should help to isolate the problem.

Regarding the threshold. It has been mentioned previously that the sensitivity is set to maximum, which means it does move from a position of slow ticking to a faster tick quite rapidly. If you want to adjust this, then you can try increasing the value of R35. Have a look at the original MiniPulse schematic. There was an internal trimmer between the opamp and R35, and a fixed resistor that's normally connected to -5V when the battery warning circuit is inactive. This trimmer allows adjustment of the threshold sensitivity

The "chatty" behaviour will only become evident if you have the threshold set to something higher than a very slow ticking. However, you won't miss any targets, as the tone increases very rapidly.

[josewashere]

Hi.
Mine does sound a bit chatty if I advance the threshold toi much but works fine otherwise. I will try to make a quick video for you tomorrow if I have time.
I do feel that the threshold needs a tweak. The point were it goes from a ticking sound to a low frequency tone sounds like its getting interference.
Best sensitivity seems to happen at the lowest threshold setting say one or two ticks per second.

[ivconic]

Qiaozhi, as author; do you have good working MPP copy to show how it is functioning?
Can you record at least 2 minutes where you gonna show plain detection, without too much detail on other things?

[ivconic]

I just finished my copy of MPP.
Switched it ON and it is working... awfully !
It is acting opposite; when i close up any metal to coil : audio fades !?
Audio is chatty and dirty, lot of "weh-wah".
Coil is 300uH.
Voltages are alright.
I tried to adjust Reject Sample Delay with trimmer and pot, all possible positions, no good results.
All components are checked and good.
I only haven't put brand new J113 there, had 2 old from a scrap and used them.
But those seems to be alright too.
I haven't exactly followed whole this topic and read all the posts, is there any already posted video with good working MPP?
Anybody made video? Anybody posted it?

[josewashere]

That's good to hear! Thanks for letting me know. I will try mine out in the field soon, maybe on a beach too. I love the handle you made for your detector, looks great. Iron I guess is always going to be a problem with a PI, being rusty in the ground makes it look like a bigger target too!

I really like this detector. The ground balance mod will really be a great addition when it becomes available. So far I have built 2 surf pi's, the chance pi, a TGSL vlf and this minipulse is my favourite for sure. One of my surf Pi does match this one on detecting distance in air. The TGSL is also very sensitive.

I remember building VLF detectors back in the 80s, we are really spoiled these days with these great designs and ease of getting them in kit form from silverdog.

[Qiaozhi]

Joop's MPP is now in the Completed Projects thread, and is the third successful build. It seems like the Build Document is doing its job!

This MPP [open-source / FREE] project has taken a lot of time and effort to get to this stage, and it's really pleasing to see your completed detectors.

How many MPPs can be constructed before the end of 2014?
I know others are currently soldering away, so don't be shy. Let's see the final results.

[Qiaozhi]

Boy, is this detector sensitive to iron!

That's why PIs are good on the beach (salt water rejection) but rubbish in a ploughed field (unless you're a relic hunter).

Have not played with the delay setting or reject knob yet.

Turning the Reject knob to a higher delay will progressively reject silver foil and then pull tabs. You'll probably need to use a 100k Reject pot (as per josewashere) to knock out the pulltabs though. This is due to the ability of the MPP to use a much lower minimum delay setting.

@Qiaozhi, will send pics of the detector tomorrow.

Thanks. The Completed Projects list is starting to grow.

[joop]

@josewashere: I have taken the detector out into the field. No problems as you have described, both on sandy soil and grass....

Boy, is this detector sensitive to iron! Been at a sweetwater lake where people go for a swim and spend one hour in the sand. Here's a finds picture:
Have not played with the delay setting or reject knob yet.

@Qiaozhi, will send pics of the detector tomorrow.

[Qiaozhi]

Qiaozhi,

I believe you want to focus on using what are known as "soft ferrites" to prevent them from being detected when used as the core of a PI probe. I have used some ferrites made of manganese/zinc with good success on a PI probe. Most cores used on DC to DC converters use soft ferrites. This tip was initiated by Eric Foster many years ago. Look up "soft ferrites" on his web site. Here is the web link: http://www.findmall.com/read.php?34,...915#msg-135915

Here is a good web link: http://www.intl-magnetics.org/pdfs/SFG-98.pdf

I used ICH ROD7.5/50 with good results on my PI machine.http://www.surplussales.com/Inductor...s/FerRods.html

Joseph Rogowski

Hi Joe,

This discussion on ferrites was started when josewashere found the MPP and both his Surf-PIs were responding to the ground on his lawn. I suggested the cause was iron contamination in the soil, and that an air test using a ferrite pot core (as a target) would prove this, as it would not be detected at higher delay settings. It was found that a ferrite core and a ferrite ring are easily detected due to their composition and shape. We were not actually discussing using the ferrite as part of the coil, just as a target.

[Davor]

Actually, even with a proper material the problem remains with the core geometry, as most of the cores have some conductivity, and thus a ring core has a pronounced eddy current that is detected as a target. E-shaped cores are OK.

[bbsailor]

Both a ferrite rod and a ferrite ring will produce an audible response from the detector, but a ferrite pot core will not.

Qiaozhi,

I believe you want to focus on using what are known as "soft ferrites" to prevent them from being detected when used as the core of a PI probe. I have used some ferrites made of manganese/zinc with good success on a PI probe. Most cores used on DC to DC converters use soft ferrites. This tip was initiated by Eric Foster many years ago. Look up "soft ferrites" on his web site. Here is the web link: http://www.findmall.com/read.php?34,...915#msg-135915

Here is a good web link: http://www.intl-magnetics.org/pdfs/SFG-98.pdf

I used ICH ROD7.5/50 with good results on my PI machine.http://www.surplussales.com/Inductor...s/FerRods.html

Joseph Rogowski

[Davor]

My lab under the stars is not producing - it is very rainy. And mosquitoes are a murder.
Soon.

[josewashere]

Ok thanks I see what you mean by pot core. I don't have one here but can get one easily enough. I will try it.

[Qiaozhi]

Hi Joop.
That would be good. I might take mine out on the weekend to see how it behaves in various types of soil. Both my surf pi's and my minipulse plus do the same thing on my lawn so it could well just be my backyard but I did the tests with the same coils. Ultimately I want to be able to use it on our gold fields here. Our gold fields are very mineralised and some have high iron levels so probably it wont work so well.

I'm still very happy with it though and will be happy if it works fine on beaches.

Regards to you from Australia

Jose

For the gold fields in Australia you will need to add a ground balance circuit, and even then you'll have problems if the ground matrix is non-homogeneous. Perhaps you'll be able to field test Davor's GB solution when he publishes the design.

[Qiaozhi]

Thanks for all the info. I tested it with a ferrite rod 8 inches long by 3/8 in diam. (200mm x 10mm diam) The type you would find in a large transistor radio and it will detect that at about 4 inches (100mm) at all delay settings though a bit less at the longer settings.
Using a ferrite tube about 1.25in long by 3/4 in diam with a 3/8 hole (30x18mm with 10mm hole) the type you use on cables for suppression it does not detect that or its just detectable when touching the coil.

thanks

Both a ferrite rod and a ferrite ring will produce an audible response from the detector, but a ferrite pot core will not.