Replies to Minipulse Plus

[6666]

Hi Davor
so you are going to build your 4017 project, was looking at trying it this weekend but will wait for you to debug.
One thing I dont understand is why the clock goes to the reset.

[greylourie]

- wolfs' procreation area (only largely without actual wolfs). If that is what you seek - you'll find it here. A stone house with open fire and all commodities 1700's style - no problem. A distant island - no problem at all. Diving? Paradise.

Sounds like paradise.

[joop]

...

So who is detecting?

[joop]

The original Minipulse coil is 8" diameter. Also, try moving the coil into different orientations and watch if the noise level changes. It may all be external noise.

I can now confirm it is the environment that produces the noise at TP3 in my case. I made a new 8 inch coil and this time added a shield. Noise is about 10 times lower. Also replaced the coil with a 1 Ohm non-inductive resistor, the noise is totally gone.

Thanks for helping out. My build is finished and working. Next I am going to put it in a box and make a complete detector.

[Davor]

Hi Davor
so you are going to build your 4017 project, was looking at trying it this weekend but will wait for you to debug.
One thing I dont understand is why the clock goes to the reset.

Don't wait for me - I have a room to paint before my summer shack start producing. I can't say when I'm starting. Off the bat I can tell you that R1 C1 time base is too short with the values presented, and better ones would be 10k in series with a 25k pot, and 3n3 capacitor.
Clock goes to reset to restart counting. 4017 then counts till Q9 goes high, and then the U3/U4 oscillator just stops ... until 555 sends a pulse to reset a counter that turns Q9 low and U3/U4 start oscillation again, and they oscillate till Q9 goes high etc.
A PNP transistor is just a clamp that limits voltage at C1 and thus dictates duration of a first transition. It is a delay till a first sample and thus GB is adjustable. With this setup sample durations are at constant ratio against the delay, so GB once set is valid for a wide variation of sample durations.

[multieagle]

Hi greylourie, if you have heaps of cat5 cable, spend the time and remove the outer insulation and split into the 4 pairs then get one length and undo it so
you have a single strand then wind your coil with it ( I have done this before, but be aware it could take 1/2h or so to do).

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

[Qiaozhi]

I can now confirm it is the environment that produces the noise at TP3 in my case. I made a new 8 inch coil and this time added a shield. Noise is about 10 times lower. Also replaced the coil with a 1 Ohm non-inductive resistor, the noise is totally gone.

Thanks for helping out. My build is finished and working. Next I am going to put it in a box and make a complete detector.

Good work! Please email me some photos of the complete build, and any comments you want to make. I will then add them to the completed projects thread. At the moment, other members are either slow in constructing, or too shy to show their results.

By the way, I forgot to mention that I've been using the original Minipulse coil, and this is shielded; which is most likely why the noise level was a lot lower.

[joop]

Okay, will do so until the complete detector is ready. It will take about a week or so....

[WM6]

By the way, I forgot to mention that I've been using the original Minipulse coil, and this is shielded; which is most likely why the noise level was a lot lower.

To what point is shielding connected?

[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.

[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.....

[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.

[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.

[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!

[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!