2nd Chance PI

[dantech]

Replace ICL7660 by TL1054.
The TL has higher maximum voltage and can work with 12V gel batteries

By the way I did a lot of tests between "race trace" type coil and dedicated basket coil.
In my humble opinion the "race" is over-advertised. Works in the same way like dedicated one
but is harder to make. Both of ones have near the same natural delay mesured by automatic measurement.

[ripsdevala]

Yes, i usually use LT1054, 7660s is too hot and cant handle 12v for too long and probably will dead, but LT is very rare here I buy used one, i burn my last LT yesterday , Never heard gel battery before, i use li ion for all setup.

[dantech]

This is the example of a gel battery
http://electropark.pl/akumulatory-ze...ah-motoma.html

The size is 97x43x52mm and capacity is 1,2Ah/12V
I use it.
For less than $6 you have quite efficient power source
The 2nd Chance PI can work more than 12 hours
Gel batteries are generally used in UPSes.
Fully charged gel battery has 13,8-14,4V depending on charge method

[baum7154]

Dan tech,

I disagree with your assessment of the racetrack 3DSS coil. Firstly I think you are not searching for small gold and the racetrack coil is specifically designed to find small gold quickly by covering a wider area with its blade search field. Because of its 4" width it does give up some depth to its 8" round 3DSS cousin but the 8" round takes more time to cover a given area. 3DSS coils self shield and this is a must for operating at sample delays below about 15us.

The original/dedicated coil you use is not shielded and this is not a problem if you don't try to operate below 15us. However if you add shield to the dedicated/original coil it will lose a significant amount of its natural speed and this doesn't lead to small gold detection. Unfortunately sample delays must be in the 5 to 10 us range for small gold (1/3 to 1/2 gram) detection and the original/dedicated coil does not operate at these short delays. This means that the original/dedicated coil is useful only for what I consider large targets such as coins, cartridge cases, and hardware. By the way any closed loop like a ring of gold or any metal is a large target because its closed loop geometry sets up strong eddy currents that are easily detectable.

Just my experiences with both coils and the 3DSS design, while harder to fabricate, is superior to the original/dedicated coil for both large and small targets.

Regards,

Dan

[eclipse]

What are the specs of the firmware (min-max pulse width), (min-max sample delay), frequency?

[dantech]

I do not search gold because in my country it is the margin of field exploration

I do not agree with you regarding 3dss. I did it according to "the art". Of course I have tested one only with coins, bullets and similar object.
There is no extra range gain and automatically measured natural delay is 32us when decicated one has 30us. The o'scope confirms it.
Of course I can increase damping and get a few
additional us but is do not makes any range gain.

[dantech]

@eclypse

main pulse width:120us
main pulse frequency:100,200,300Hz (in the menu it is called coil sweeping speed: slow, normal, fast)
main pulse delay: auto or manual 3 - 99us

Power consumption in the slow, normal and fast mode: 70, 90, 110mA (if I remember well)

By default the detector is set to automatic coil delay detection mode. Position just below 3us. It works wery well

I find that frequencies higher than 400Hz and pulse width other than 100-140us in PIs has no sense.
Frequency forces coil sweeping speed only and coil should be saturated well (I mean pulse width).
Shorter pulses width make measurements unstable (especially for discrimination)
and wider pulses make increased and unwanted power consumption only

[eclipse]

Thanks for the info!

[Wahyu]

@eclypse

main pulse width:120us
main pulse frequency:100,200,300Hz (in the menu it is called coil sweeping speed: slow, normal, fast)
main pulse delay: auto or manual 3 - 99us

Power consumption in the slow, normal and fast mode: 70, 90, 110mA (if I remember well)

By default the detector is set to automatic coil delay detection mode. Position just below 3us. It works wery well

I find that frequencies higher than 400Hz and pulse width other than 100-140us in PIs has no sense.
Frequency forces coil sweeping speed only and coil should be saturated well (I mean pulse width).
Shorter pulses width make measurements unstable (especially for discrimination)
and wider pulses make increased and unwanted power consumption only

good

and what spec sample window?

[dantech]

You can find it in the menu as VDI sampling 1 and 2

[baum7154]

I do not search gold because in my country it is the margin of field exploration

I do not agree with you regarding 3dss. I did it according to "the art". Of course I have tested one only with coins, bullets and similar object.
There is no extra range gain and automatically measured natural delay is 32us when decicated one has 30us. The o'scope confirms it.
Of course I can increase damping and get a few
additional us but is do not makes any range gain.

--------------------------------------------------

What 3DSS coil did you make, 8" round or 4" X 12.5" Racetrack? It is only right to compare performance of 3DSS 8" round coil to the original/dedicated 8" round Chance PI coil each having its proper critical damping resistance. Coil diameter is primarily what gives detection depth on a capable detector. However larger coil diameter also spreads signal power over a greater area and limits small target detection. What wire did you wind your 3DSS coil with, solid conductor enamel 24ga or teflon insulated 24 gauge or something else? What feed line did you use? My oscilloscope shows the 8" round 3DSS coil flyback settling in 6us, not the 32us you mention above (see Chance PI Build post 53 photo 1). Also in this same post is a picture of the original Chance PI single stage amp output that adds 9us to the signal output fed to the A/D because the amp goes into saturation. For this reason I designed a 2 stage amp that does not saturate and is detailed in the same thread. One more thing this 8" 3DSS round coil was properly damped using a 1040 ohm resistor.

I am trying to clarify for followers of this thread needing a gold detector what it will take to make the '2nd Chance' of this thread into a gold detector as very much effort has been spent in the original 'Chance PI Build' thread to achieve this goal. It would be a shame if others are building this 2nd Chance thinking it will detect small natural gold, as it will not.

I appreciate the firmware changes you are making but it seems that you are disregarding the previous work that has been done to make Chance into a gold detector and that starts with a different coil and damping. Perhaps we need to have two Chance PI versions, one for artifacts and one for gold. I have found though that the improvements and modifications made to detect gold also improve detection of other kinds of targets. If you don't have small natural gold to use as a test target a 6mm square piece of the sidewall of an aluminum soda can is a very good simulator. My Chance PI with v1.2.1 firmware sees this target using a 3DSS racetrack coil at 2.75" with the coil resting 3/4" over soil. The 8" round 3DSS coil sees it at 1" farther than the Racetrack. My original/dedicated Chance Pi coil does not see it at all. If the 6mm square AL target is not detected a 1cm square of the same material is easier to detect.

Best regards,

Dan

[dantech]

I did 11x33 cm racetrack 3dss, copper wire 0,8mm , insulated by painting (like in trafo). I have tested different dampings also. Total resistance is exactly the same like dedicated coil. it means 1 ohm. Feed line is simetric in both cases. I do not find that concentic feed line is better - also tested. I have tested also your 2 stage amplifier and gain was .... hmmm... -3 to 4 us. Nothing significiant for artifact. Like I said I do not use 2nd Chance to look for gold. So I am totally not interested to optimize 2nd Chance for it. I do not have even conditions to test it.
Gold resources in Poland are rather poor. 1 square cm can wall is detected from 5-6 cm in both cases. Personally I do not believe in so quick decays, I did too much tests.

General target for me is metal discrimination for and artifacts

Did your try v016 in your environment? I am very interested to know the results.

[baum7154]

--------------------------------------------------

I am trying to clarify for followers of this thread needing a gold detector what it will take to make the '2nd Chance' of this thread into a gold detector as very much effort has been spent in the original 'Chance PI Build' thread to achieve this goal. It would be a shame if others are building this 2nd Chance thinking it will detect small natural gold, as it will not.

Perhaps we need to have two Chance PI versions, one for artifacts and one for gold. I have found though that the improvements and modifications made to detect gold also improve detection of other kinds of targets. If you don't have small natural gold to use as a test target a 6mm square piece of the sidewall of an aluminum soda can is a very good simulator. My Chance PI with v1.2.1 firmware sees this target using a 3DSS racetrack coil at 2.75" with the coil resting 3/4" over soil. The 8" round 3DSS coil sees it at 1" farther than the Racetrack. My original/dedicated Chance Pi coil does not see it at all. If the 6mm square AL target is not detected a 1cm square of the same material is easier to detect.

Best regards,

Dan

-----------------------------------------------

To clarify from my last post:

"I am trying to clarify for followers of this thread needing a gold detector what it will take to make the '2nd Chance' of this thread into a gold detector as very much effort has been spent in the original 'Chance PI Build' thread to achieve this goal. It would be a shame if others are building this 2nd Chance thinking it will detect small natural gold, as it will not. "

HOWEVER...Chance PI will detect small natural gold with the proper coil and damping to allow it to operate in the range of 10us and below. Other modifications such as the 2 stage amplifier will allow the detector to operate with sub 10us sample delays. The firmware modifications that Dantech has made should be very useful in operations below 10us as well. Original Chance firmware did not allow sampling below about 9us but Dantech has changed firmware to allow sampling to begin in the range of 5us (with a very fast coil and critical damping) and this is significant for very small natural gold targets.

I have not yet installed V016 in my Chance PI but I am anxious to get it done as soon as time permits. I will post results of the firmware upgrade here.

Dantech have you tested discrimination on a common bottle cap, otherwise known as a Crown Cap (a rusty one would be the best test)? This target is notorious for discriminating as Gold/Aluminum/Nickle at low signal levels but does discriminate properly as IRON at high signal strengths. I'd like to know how the new firmware handles this target.

Dan

[dantech]

No I did not test Crown Caps. I understand that is the brand of beer unavailable in my country site.

But I have tested 2nd Chance on the beach when there were a lot of caps and if I remember well caps were on 3-4th position on the VDI. There was kind of caps on 1-2nd segment.

Probably those caps were made of thinner plate. Generally there was not any problem with caps distinguishing.

I find that v016 is very stable (original v121 was not) and is one fully compatible with old hardware, so if you state that you have some good results with two stage amplifier and 3dss coil you do not have to affraid that v016 will not work

[dantech]

v017 is released. Cosmetic change