Replies to Minipulse Plus

[ivconic]

SL files look nice

Makes my life much easier in process when putting components on pcb.
I use to print such picture on paper and than work is much easier.
Would be even better if i had color laser printer, by now i have only b/w laser.

[bernte_one]

SL files look nice

[ivconic]

Thanks Ivica,

I've added your files to the Minipulse REV-B thread for use by other Sprint Layout users.

Please have a look at the REV-C PCB. This contains 2 minor fixes (see MiniPulse REV-C thread) and the addition of TP10 for connecting a ground probe. If you make these changes to your Sprint Layout file, I will add that to the REV-C thread as well.

[josewashere]

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

[joop]

From what I know, the ferrite rod is composed of sintered MnZn or NiZn compositions and the RF suppression tube is made of iron powder, small iron particles glued together.

I might be able to help out in a couple of days. My detector is ready but can't take it outside yet... I am waiting for the coil cable to arrive.

[josewashere]

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

[josewashere]

Emailed you the pics

[Qiaozhi]

If it was not done in Sprint Layout; it does not exist for me!
Nobody else did it; so i had to do it, again!
Recently i had to switch on Sprint Layout 6, so this was good exercise for me.
Personally i don't like the chosen size and spacing for 470nF capacitors... but that's just me!

Thanks Ivica,

I've added your files to the Minipulse REV-B thread for use by other Sprint Layout users.

Please have a look at the REV-C PCB. This contains 2 minor fixes (see MiniPulse REV-C thread) and the addition of TP10 for connecting a ground probe. If you make these changes to your Sprint Layout file, I will add that to the REV-C thread as well.

[Qiaozhi]

Hi Guys. First time user of this forum though I have been looking here for a while. I recently completed the minipulse plus and I have been playing with coils that were leftover from my surf pi build.
I have a couple of questions.
First all my mpp spec's when viewed on a scope are as per the rev c document. I can however set my sample delay to about 7us before it drops out. I am using a coiltek 11 inch mono and a home made 8 inch mono coil. Coiltek is a commercial coil designed for use with minelab pi detectors.

Yes, that's correct. The MPP can sample at sub-10us delays. However, please be aware that (according to the datasheet) the monostables are capable of a minimum pulse width of 10us. But in general they can go lower than that before cutting out.

I changed my external sample delay pot to 100k in order to have a greater adjustment range. 7us to 32us.

That is as expected.

Does the on board trimmer need to be set to 22us delay as per the rev c document? or can I just leave it at 7us?

Setting the on-board trimmer to 22us is only for initial testing. After that you can set it to whatever minimum delay you prefer. If, for example, your coil cannot sample below 10us, then set the internal trimmer to that value. The external Reject pot simply allows the user to increase the sample delay to a higher value, and hence eliminate unwanted targets based on conductivity.

When testing the detector on green grass in my back yard I get a signal as the coil nears the ground. I get this even at the longest sampling delay and yes both coils are shielded. For test purposes I added extra shielding to my home made coil but even though it dropped the sensitivity a bit it still sounds off when the coil nears the ground. The SAT does bring the threshold back to normal if I leave the coil on the ground but of course it sounds off again if I rise the coil a bit. Is this normal behaviour for this type of detector?

If the detector is sounding off as the coil nears the ground when on its longest delay, then the soil is most likely contaminated with iron. I had a similar problem the first time I built a Hammerhead detector. Take a large ferrite core and wave it in front of the coil. If there is no detection, then the soil is iron-infested.

I haven't tested it on just soil without grass or out in the gold fields yet! Once I know the detector is working normally I want to try swapping out opamps. Currently getting a small gold ring (just detectable) at about 12 inches (30cm) and a can at about 100cm in air. (11 inch mono)

That's a good result.

Qiaozhi suggested emailing him some images of completed builds but I can see any way of doing that here.

Please send photos to [email protected]

Well done on a successful build, and doubly well done on being the second person destined for the Completed Projects thread.

[ivconic]

If it was not done in Sprint Layout; it does not exist for me!
Nobody else did it; so i had to do it, again!
Recently i had to switch on Sprint Layout 6, so this was good exercise for me.
Personally i don't like the chosen size and spacing for 470nF capacitors... but that's just me!

[josewashere]

Hi Guys. First time user of this forum though I have been looking here for a while. I recently completed the minipulse plus and I have been playing with coils that were leftover from my surf pi build.
I have a couple of questions.
First all my mpp spec's when viewed on a scope are as per the rev c document. I can however set my sample delay to about 7us before it drops out. I am using a coiltek 11 inch mono and a home made 8 inch mono coil. Coiltek is a commercial coil designed for use with minelab pi detectors.
I changed my external sample delay pot to 100k in order to have a greater adjustment range. 7us to 32us.
Does the on board trimmer need to be set to 22us delay as per the rev c document? or can I just leave it at 7us?
When testing the detector on green grass in my back yard I get a signal as the coil nears the ground. I get this even at the longest sampling delay and yes both coils are shielded. For test purposes I added extra shielding to my home made coil but even though it dropped the sensitivity a bit it still sounds off when the coil nears the ground. The SAT does bring the threshold back to normal if I leave the coil on the ground but of course it sounds off again if I rise the coil a bit. Is this normal behaviour for this type of detector?
I haven't tested it on just soil without grass or out in the gold fields yet! Once I know the detector is working normally I want to try swapping out opamps. Currently getting a small gold ring (just detectable) at about 12 inches (30cm) and a can at about 100cm in air. (11 inch mono)
Qiaozhi suggested emailing him some images of completed builds but I can see any way of doing that here.
Thank's guys!

[Qiaozhi]

Here is a little construction tip for those building the kit.

In step 6 to initially setup R6 100k for a delay of 22uS you need a CRO
however if you dont have a CRO then try this.

Before you install R6, first adjust the pot so its approx 50k between middle and outside pins
after you solder it leave the legs long.

Remove any power, and do not connect anything to PL3 .

Now useing a good multimeter adjust R6 so it reads about 64.7 K between the middle
and right hand legs of the pot, this should, if all things are correct, get you close to 22uS.

Also (as described in the Build Document) you can go ahead and complete Step 7, and then adjust R6 to give a DC level of around 500mV at TP4.
However, 6666's method will provide a more accurate setting.

[6666]

Here is a little construction tip for those building the kit.

In step 6 to initially setup R6 100k for a delay of 22uS you need a CRO
however if you dont have a CRO then try this.

Before you install R6, first adjust the pot so its approx 50k between middle and outside pins
after you solder it leave the legs long.

Remove any power, and do not connect anything to PL3 .

Now useing a good multimeter adjust R6 so it reads about 64.7 K between the middle
and right hand legs of the pot, this should, if all things are correct, get you close to 22uS.

[greylourie]

Just a thought, no need to remove outer casing, just connect the coloured wires in series to yield two leads.

Had some problems when I did that. You can see the scope screenshots. Coil was roughly 8", made up of three laps - with the wire joined in series to make one length. Had to strip out the built in shielding - it didn't have that when i made a computer patch cable a few years back. Pity, because it was a nice way to improvise a basket weave type coil. I will have to make another coil using more conventional bundle winding. And see if I get better waveforms.....

[Qiaozhi]

To what point is shielding connected?

It's connected to 0V, which is the battery positive. You can physically connect it to either PL2 pins 1/3 or PL4 pins 1/3.