Minipulse Plus Rev My time has come!

[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

[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]

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

[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]

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?

[mushaba]

As for the extra 6us I believe is the time that the ic goes from a level to another,can it be tweaked to be accurate?

[green]

Some scope pictures adjusting damping. Two different Tx coils, scope lead clipped to Tx hot lead insulation.

[mushaba]

Some scope pictures adjusting damping. Two different Tx coils, scope lead clipped to Tx hot lead insulation.

Thanks green for the usefull info.I used TP3 (I think) for the damping procedure,my waveform looks mostly like the o e down at right...
Tommorow I will try to dump again and measure from the "Hotpoint" of the resistor...Thanks again for your response!Do you think with better coil I can achieve more precise timmings?

[dbanner]

Just out of curiosity, which 4538 chips did you use? I mean the whole name. The small discrepancies could be result of which type used.
CD4538, hcf4538, rca4538, mc14538 etc, then bp, bcp, etc. Don't know for sure, but try swapping out for different manufacturers if you have any in stock.

[mushaba]

Just out of curiosity, which 4538 chips did you use? I mean the whole name. The small discrepancies could be result of which type used.
CD4538, hcf4538, rca4538, mc14538 etc, then bp, bcp, etc. Don't know for sure, but try swapping out for different manufacturers if you have any in stock.

Thanks dbanner for your reply,currently I'm at work tommorow I ll be at my homeshop and I will look it for sure.I bought the kit (pcb+parts) from diydetectors cause TME was out of stock to some parts..I also believe that timmings issues are due to ic quality..We should use cmos ic's ...I've checked on arrival all parts except the ic..

[dbanner]

I'm not expert, but difference between 10uS and 15uS is sooo small.
I feel that different solder quality and fluxy residues on PCB could steal a microsecond or two.
Clean board from flux. Nice and clean.
Also, I never considered the effects of sockets vs directly soldered chips.
I never worried much about soo small sample delays.
Just thinking out loud some things that might be considered when dealing with such tiny margins.
Also what kind and how long wires to delay pot. Don't really know, but not sure what effect if any these things mentioned might have on depriving you of a few microseconds here and there.
Otherwise tweak the component values to get the results you want.

[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.

Thanks godigit1,took me sometime,learned a lot of things and come down to some conlcusions.As for ringing the only time i saw on the scope "ringing" i was monitoring TP3,a very helpfull image on green's post took measurments at hot side of the coil.

As far as the gain pot .
Maybe there is a resistor or pot not right??

Happy happy happy!!!!!!!!!!!!I dont know if it is correct but i cut one side of the pot and bang!

[mushaba]

Just out of curiosity, which 4538 chips did you use? I mean the whole name. The small discrepancies could be result of which type used.
CD4538, hcf4538, rca4538, mc14538 etc, then bp, bcp, etc. Don't know for sure, but try swapping out for different manufacturers if you have any in stock.

Unfortunatelly i dont have stocked another 4538...Mine is the HFC type by St came from diydetectors.co.uk within the kit.


As i see from image below its a "faster" type than MC14538BCP ..

[mushaba]

Some scope pictures adjusting damping. Two different Tx coils, scope lead clipped to Tx hot lead insulation.

Well here are mine readings (this time dumping resistor 1610Ohms)




How do they look??Comparing to the photo you've sent me mine has a steep rising edge with something weird on the top left edge..

[mushaba]

I'm not expert, but difference between 10uS and 15uS is sooo small.
I feel that different solder quality and fluxy residues on PCB could steal a microsecond or two.
Clean board from flux. Nice and clean.
Also, I never considered the effects of sockets vs directly soldered chips.
I never worried much about soo small sample delays.
Just thinking out loud some things that might be considered when dealing with such tiny margins.
Also what kind and how long wires to delay pot. Don't really know, but not sure what effect if any these things mentioned might have on depriving you of a few microseconds here and there.
Otherwise tweak the component values to get the results you want.

Yes will do that,i will clean flux ....I should be able to take the correct test measurments and after that i will make a very nice construction and housing for a finish.