Minipulse Plus Rev My time has come!

[mushaba]

Im glad you figured it out.
Almost every question we can has been ask before its just a question of finding the posts.
There is a thread where Tepco If memory serves put a short film of the damping resistor adjustment. Its a old thread so I havent been able to find it.
You want to adjust your damping pot to you see the ringing then adjust it until the ringing just disappears.
As far as the gain pot .
Maybe there is a resistor or pot not right??

Yes exactly,I put the first resistor network (resistor parallel with resistor+pot in series) as I read with 1.2k resistors and I couldn't see it..So I put a 4.7 pot I had laying around and the ringing effect was clearly visible.If you find the video or if you have a thread in mind please post because as I see correct damping is 50% if the building success..

As for the gain pot ,when I replaced the R35 with a fine trimmer I double checked the r32 c18 and c19 values are correct...I should look it up further..

I'm reading post about the basket coil...why they call it 3dss?

[godigit1]

Im glad you figured it out.
Almost every question we can has been ask before its just a question of finding the posts.
There is a thread where Tepco If memory serves put a short film of the damping resistor adjustment. Its a old thread so I havent been able to find it.
You want to adjust your damping pot to you see the ringing then adjust it until the ringing just disappears.
As far as the gain pot .
Maybe there is a resistor or pot not right??

[mushaba]

Now its time to answer to myself (probably the beggining of madness

Think i found the root of my problems..

At first i dumped my coil near 990 Ohms

After spending sometime reading older posts, came out my coil is piece of junk,it damped with 2400 Ohms resistor.. I will try to build a basket coil.

Now,at Step 6 says 1ch at TP2 and 2ch at TP6.According to Fig.10 there should be a delay (Main Sample Delay) of 10us.As you see from the photo below the two curves have no delay between them...Thats probably why i dont sample gold right?

[ATTACH]45909[/ATTACH]

Totally misunderstood..The sample delay PULSE (TP6) is 10us,i was looking for 10usec delay between main pulse and sample delay pulse..

Also between main pulse (TP2) and delay pulse EFE (TP there is a 10usec spacing.The thing i thought i was doing wrong was very clearly written on top of page 6 of instructios about rev e "EFE=100us+main sample delay" This correctly is 110us (i mseasure 116us where those 6us comes from..????)

My wrong measurment at TP9 corrected by replacing R35 with a fine 5k trimmer (i saw an older post George made such a suggestion),so my readings at TP9 and TP10 are identical 10us.

My timmings dont follow George's instructions.Step 5 i dont see voltage drop .

My bad,i see voltage drop...

The only thing thats left is that with the gain pot i go from 10us to nearly 30us not 52us as written on instructions,should i blame the coil??

Your thoughts gentlemen

[mushaba]

Yep, something about the Links in chain. It's like a small circular Transformer Coil Cancels out the Eddy Currents . If the chain has any type of Fob or Charm they show up way better then just a small chain alone.

Homefire great to hear from you in here!!

[mushaba]

Your coil Is under damped a bit.

How did you figure that?Im still not getting the "damping" precedure right...I put the resistor and pot network i've mentioned above and tried to smooth out the curve (TP3) when going down to 0 V.Do you have a post in your mind that expains the coil damping for dummies??

One reasone you are not seeing gold beacuse you are using a small chain. Even a good VLF has a hard time with this target. A metal detector only sees one link in the chain and the one closest to the coil.

My chain has also a cross near to a gramm or more..

Your coil is 20 guage wire thats a bit thick in my opinion

The wire is AWG 24 (0,50mm metric) coil aprox 200mm diameter.

This video from another member Tibuck19 shows how minute the voltage change is at the integrator for gold. its hard to see.
Your can is huge that is why you see a full response and the gold is invisible.
https://www.youtube.com/watch?v=OyS8sfv0XJ0&t=302s

Thats a great video should help me compare some scope readings..Dont you think something else is wrong?? My timmings dont follow George's instructions.Step 5 i dont see voltage drop .Step 6 shorted PL6 both widths are 15us not 10 us.Pot adjusts from 15 to 30us not 10 to 57us.Is that coil damping related or due to parts accuracy ??

Also you should hook your coil up directly you test cable is way too long.
Good Luck

Ok,i will shorten that,its an RG58 military grade

[homefire]

Yep, something about the Links in chain. It's like a small circular Transformer Coil Cancels out the Eddy Currents . If the chain has any type of Fob or Charm they show up way better then just a small chain alone.

[godigit1]

Also you should hook your coil up directly you test cable is way too long.
Good Luck

[godigit1]

Your coil Is under damped a bit. One reasone you are not seeing gold beacuse you are using a small chain. Even a good VLF has a hard time with this target. A metal detector only sees one link in the chain and the one closest to the coil. Your coil is 20 guage wire thats a bit thick in my opinion
Ive found chains but always by the clasp the chain porblematic.
Use a ring to set up.
This video from another member Tibuck19 shows how minute the voltage change is at the integrator for gold. its hard to see.
Your can is huge that is why you see a full response and the gold is invisible.

https://www.youtube.com/watch?v=OyS8sfv0XJ0&t=302s

[mushaba]

Also found at Step 5

[mushaba]

Think i found the root of my problems..

At first i dumped my coil near 990 Ohms

Now,at Step 6 says 1ch at TP2 and 2ch at TP6.According to Fig.10 there should be a delay (Main Sample Delay) of 10us.As you see from the photo below the two curves have no delay between them...Thats probably why i dont sample gold right?

[Qiaozhi]

What do we mean by "damp"????Not so good with this term

If you remove the damping resistor and look at the pre-amp output, you will see lots of oscillations that will gradually die away. The damping resistor "damps" these oscillations so that the pre-amp output transitions smoothly from saturation to 0V. The key thing here is to achieve "critical damping". If the signal is slightly under-damped, it will overshoot the 0V line before settling back down. If the signal is over-damped, the exponential curve will move to the right. What you are trying to do is remove the huge signal induced by the flyback when the MOSFET opens in the most efficient way, leaving enough time to sample any target signals before they disappear.

In my case i do not see this happens,am i right?

Try fitting a higher value damping resistor, such as 2k. You should see it then.

Taking measurements again and following the steps i've noticed two things:

1) At Step 6 TP2 pulse level is -12V and pulse goes to 0 ... TP6 level is at -5V and pulse goes to 0,is this correct?

Yes, that's correct.

2) At Step 7 TP4 the DC level goes to 0 when a target is near the coil , this is clearly wrong..

That's not correct.
I would suggest comparing the pulse widths at TP9 and TP10. They should be the same width, but occur at different times.
Do you have Q1 and Q3 inserted correctly?

[mushaba]

Try rotating your coil to see if the noise on the pre-amp output signal changes. The noise is usually lower when the coil is in a horizontal (rather than vertical) position.

Ok

You need to adjust the damping resistor to critically damp the signal.

What do we mean by "damp"????Not so good with this term

The noise you can see on the scope is not the "ringing" you are trying to eliminate. After the pre-amp comes out of saturation, the signal will exponentially decay towards the 0V line. If the damping resistor is too small, this signal will overshoot the 0V line before settling down. This is what's called ringing.

In my case i do not see this happens,am i right?

To reduce the noise pickup, you also need to shield your coil.

Im waiting foe a cooper tape i ordered,i only have a shinny type and i read that its not suitable for the faraday shield.


Taking measurements again and following the steps i've noticed two things:

1) At Step 6 TP2 pulse level is -12V and pulse goes to 0 ... TP6 level is at -5V and pulse goes to 0,is this correct?
2) At Step 7 TP4 the DC level goes to 0 when a target is near the coil , this is clearly wrong..

[Qiaozhi]

Try rotating your coil to see if the noise on the pre-amp output signal changes. The noise is usually lower when the coil is in a horizontal (rather than vertical) position.

You need to adjust the damping resistor to critically damp the signal. The noise you can see on the scope is not the "ringing" you are trying to eliminate. After the pre-amp comes out of saturation, the signal will exponentially decay towards the 0V line. If the damping resistor is too small, this signal will overshoot the 0V line before settling down. This is what's called ringing.

To reduce the noise pickup, you also need to shield your coil.

[mushaba]

There is a lot of noise or ringing,is that because my coil isnt damped as it should?


Try turning off any florescent lights anywhere near or other electrical equipment maybe.

Yeap,the coil is not properly damped because i dont know how it looks the output waveform on TP3.I'm gonna try put instead of the R4 the damping resistance setup i found on "Making a Fast Pulse Induction Mono Coil" by Joseph J. Rogowski.



Also the specs of my coil wire are:

.

Before i do the damping i tryed turning off the florescent lights as godigit1 suggested and the noise became smaller



Also the detecting lenght of a soda can increaed from 40cm aprox. to 60cm..

A short video presenting the build so far (with lights on)

https://youtu.be/fPpfm3D6Jqo

A video after i turned the lights off

https://youtu.be/_hjVybY9ZmU

Im pretty sure im doing something wrong with the timmings

Any help will be appreciated

[mushaba]

What is the correct way to damp the coil.I saw a schematic with 1,2Kohms in parallel with 1,2K and 4,7k in series,this should make it flat?
It detects a can of soda at 40cm,the weird is that it can't detect anything gold..