Replies to Minipulse Plus

[perzo]

آHi All this good pcb Dedicated to all friend

[timekiller]

Hello This is my first post in this forum.
I have 2 surf pi working machines made by me on a breadboard pcb board. All work great, and now I made my mini pulse. On the same custom board. Use modified astable oscillator and 7660 supplied 14 volts in 7809. Power in lm350 and 4 lipo batery .I have no oscilloscope, but everything went right. About 25 cm piece 1e stable recording and about 30 cm maximum .Coil turns 18 AWG 22 - 25 cm . Minipulse rev D is an excellent machine, but what is the potential ? What would improve in my case dd or balance coil ?

[LukeJ]

Hello timekiller.... Like you, this is also my first post to the forum. Thank you to all who share their knowledge and experience here !!

I recently purchased a MPP kit from Silverdog. I took my time and followed the instructions and what do you know ??? It works !!

I'm now waiting for the bits and pieces to arrive so I can attempt KRinAz's modifications. I hunt in the same types of ground....

Thank you for a well thought out project !!

Luke

[Qiaozhi]

Hello timekiller.... Like you, this is also my first post to the forum. Thank you to all who share their knowledge and experience here !!

I recently purchased a MPP kit from Silverdog. I took my time and followed the instructions and what do you know ??? It works !!

I'm now waiting for the bits and pieces to arrive so I can attempt KRinAz's modifications. I hunt in the same types of ground....

Thank you for a well thought out project !!

Luke

Well done! You are now living proof that following the instructions actually works.

If you post some pictures and a short description of your experience, I will add you to the Completed Projects thread.

[bernte_one]

helloe perzo,

can you upload pcd file (is it sprint layout?) as zipped file as Attachement here in this thread thx

[Teleno]

Anyone having Earth Field beeps in their MPP rev. D?

I've tried swinging the coil up in the air and it beeps. It does even at maximum delay. When swung slowly the beep goes away, so I thought it might not be cancelling EF properly.

Does anyone's MPP behave the same way?

[Goaty]

Anyone having Earth Field beeps in their MPP rev. D?

I've tried swinging the coil up in the air and it beeps. It does even at maximum delay. When swung slowly the beep goes away, so I thought it might not be cancelling EF properly.

Does anyone's MPP behave the same way?

I know this is an old post but did you solve this problem?
Mine is doing the same and, so far, I haven't found a solution

[kt315]

sorry but MPP is simple design for beginners for getting new experience and starting the new hobby (for you).
you have to start to do new project, maybe hammerhead, with GB tuning advantage. do not worry, you went successfully through the first stage and are ready
overcome next frontier. you are on right way amigo. we all go through the stages in our life. (ontime i did have AT286 and it was very good PC. then
i bought 386SX33 and it was better. then i bought 486DX66 and it was still better, etc. and we notice - on every stage we just wasted our money)
the most valuable for you is the experience, not gold you are trying seeking by MPP on the beaches. so Eric Foster also doing MPP at time it was good start for him and ascent in career and the ascent to understanding of the meaning of pulse induction.
then he did other detectors and went to modern ones we know. we do not have more modern his schematics to give you right now (i hope they will go).
you must understand every schematic is huge job - to buy the detector, to desolder the board, to draw the diagram, to write detailed report how-to-do
etcetera etcetera. that you repeat MPP is just your appreciation of this job.

[Wahyu]

I know this is an old post but did you solve this problem?
Mine is doing the same and, so far, I haven't found a solution

Maybe this solution http://www.geotech1.com/forums/showt...amp#post219381

[Goaty]

@ kt315

Thanks for the words of wisdom kt.
Yes, this metal detector caper has opened up a whole new aspect of electronics for me.
I have been a hobbyist/part-time instructor/ amateur radio operator/ alarm tech in electronics for close on 50yrs and still learning. Metal detector technology has turned out to be a whole new ball game!


My biggest problem nowadays is that since retiring I don’t have time to do everything I want .

I’ve built 3 or 4 different detectors but seem to spend more time building them than actually using.


BTW, my intro to computing came mid way through my teaching career when it involved marking ‘punch cards’ and then sending them off to a computing centre to be processed. The success rate with a class of 30 kids was not very high!


@Wahyu


Thanks for that link – more good info there to add to my collection.
I’m starting to formulate a plan of attack now – almost time to fire up the soldering iron.

[Goaty]

Just a (lack of ) progress report :-


After much reading forum posts and studying the MPP circuit diagram I have listed my options for dealing with this problem -


(1) Fit a low value balance trimpot between C12 (wiper) and R24, R25.


(2) Measure and match C13 & C14 (470nF)


(3) Match the parameters of Q3 and Q4 JFETs.
I’m not sure just which parameters – possibly IDSS and Vgs, and how close in value they should be.


(4) Match the ‘main’ and ‘sample’ pulse widths more accurately.


(5) Play with the value of C12 (coupling cap.) as suggested in a post by Eric. He suggested an electro up to 22uF or even DC coupling and that scoping across R10 should show a flat DC baseline. From memory, I think one of the pulses in this area showed a slight overshoot – will have to go back and check that again.


Can anyone suggest any others?

[Goaty]

I've finally found the time to start removing and checking some of the components in the sampling integrator section and would appreciate some advice on a couple of my findings -

(1) The jfets Q3 and Q4 give the following results on my component tester - Q3 IDSS 1.5Ma Vgs 1.1v, Q4 IDSS 1.5Ma 1.1V. Are these closely matched enough?

(2) R20 & R23 measure 6k25 ohms each instead of 6k8. Should I change them to 6K8 even though they match.

I have measured C13 and c14 they match OK at 450nF instead of 470nF.

Any advice would be appreciated.

[Qiaozhi]

I've finally found the time to start removing and checking some of the components in the sampling integrator section and would appreciate some advice on a couple of my findings -

(1) The jfets Q3 and Q4 give the following results on my component tester - Q3 IDSS 1.5Ma Vgs 1.1v, Q4 IDSS 1.5Ma 1.1V. Are these closely matched enough?

(2) R20 & R23 measure 6k25 ohms each instead of 6k8. Should I change them to 6K8 even though they match.

I have measured C13 and c14 they match OK at 450nF instead of 470nF.

Any advice would be appreciated.

I don't understand why you're having problems with Earth Field Elimination on the MPP. It should be working ok. As you can see from the Completed Projects list, several others have not experienced this problem.

I'm wondering whether you're chasing a red herring, and you either have a fault on your board or there's something up with the coil.
What are the details of your coil?

[Goaty]

@ Qiaozhi

Yes, I'm sure I'm missing something obvious but at least I'm learning as I investigate.

I contacted Teleno as he was having similar problems with his but he had not found a solution either.

I think I will try a more closely matched pair of jfets next before giving the sample pulse generator section another going over.

A bundle wound coil I tried earlier gave the same effect as the 3DSS I have on it now so I assumed that the coil was not part of the problem.

BTW, the resistances quoted above for R20 & R23 were 'in-circuit' values - when I pulled them and re-measured they were both 6k8.

The puzzling thing is that the rest of the circuit works quite well - the detection depth is as good, if not better that, the Surf PI 1.2.- or I could just learn to ignore the falsing and learn to swing more slowly!

Anyway, thanks again for your suggestions.

Cheers
Goaty

[Goaty]

Jfet swap (Q3 & Q4) made no difference to falsing - starting to think sampling integrator section is OK.

Tried tapping/bumping both coils - no problems.

Next!!!!????