chance pi build

[dantech]

I would like to inform that diodes HER208 can be replaced by UF4007 (recovery = 75ns, 1A, 1000V)

[baum7154]

Yes, the UF4007 is better as at 17pf, it has only about half of the junction capacitance of of the HER208 at 4 volts.

Thanks,

Dan

[baum7154]

@baum7154
I was thinking about shortening of main delay only whilst using faster coils than dedicated ones.
You have to take into account one potential problem.
When you overclock Atmega you will get proportional delay in the whole process.
But we have to remember that
there is 2nd series of 16 pulses and 2nd constant delay. That 2nd pulse series and 2nd delay is used to distinguish metal and balance ground.
So using fast coil and shortening main delay only we can
impair and even lose metal distinguishing and ground balancing features.
Entire process in Chance PI is still optimized for dedicated coils.

So, you have to verify the issue with v164.
I do not have faster coil than dedicated one and I do not have 2 stage preamp also.

____________________________________________

My purpose in using a faster clock was to get CHANCE to operate at 7us when set at the lowest limit of '10' with the V1.2.1 firmware. However since you have opened the Guard Interval (Sample Delay) in your firmware all the way down to a setting of '1' (maybe 5us) overclocking is no longer necessary.

Thanks,

Dan

[dantech]

Here is v165.

There are two different and alternating one by one cycles. Odd cycles measure main pulse and show signal strenght bar. Even cycles measure ground and kind of metal. In the previous versions the delay time from menu was changed only for the odd cycles. Even cycles had contstant delay = 30us.

Now in the even cycles delay is also depending from menu setting. In my opinion it is more right than constant value regading different speed of coils.

I need reports from field how my release work

[baum7154]

Thank you dantech,

I have read the translation of your entire Polish thread translated by Google.

One thing I see is you report that the detector and coil have difficulty with Guard Interval (Sample Delay) settings below perhaps a value of '20' because you believe the detector is possibly picking up ferrites. Initially I too had this problem with the V1.2.1 firmware but it is not ferrites. It can be corrected by proper coil damping and this will allow the detection of small gold of about 1/4 to 1/3 of a gram. A good test target to simulate this is a 6mm square cut from the side wall of an aluminum can, not the thicker top or bottom of the can material. The 3DSS coil in the CHANCE PI COIL thread at a value of 328uh would be properly damped with a resistance value of about 1060 to 1100 ohms and not the original 390 ohm or even the 680 values of the redesigns. A 1cm square of this same material is a much easier target to detect if necessary. These types of targets have been somewhat accepted as standards for detection sensitivity on these forums. Proper coil damping allows the quickest dissipation of coil energy and consequently the shortest possible sample delay settings.

Best Regards,

Dan

[dantech]

@baum7154
What do you mean by "ferrites"?

[baum7154]

Typically iron compounds such as magnetite, black sands, etc.

[dantech]

Hmmm. I test delay period in the air. Eg. I set 28 us and than approach object to the coil. Every 10 segments of signal bar are lit and overdive signal is audible. Then I set 27 us and make the same procedure but suddenly shall we say on 8th segment od 10 ovedrive signal is audible. This is sign that natural delay of coil is reached. When I set 26us I see and hear full sinal strenght . It means that ADC probes unuasable range of coil response.

So, I do not uderstand where is the ferrite issue?

[baum7154]

Perhaps I am referencing an earlier comment in your thread before the current V1.6.5, but still for a very fast 3DSS coil critical damping must be performed in order to get below 10us delay necessary to see very small gold as this small fast metal decays in well under 20us. Have you tried to detect the 6mm square of aluminum can side wall yet? I am anxious to try out your new firmware but don't have a setup for programing the Atmega chip. I do have a spare Atmega chip with the old V0.8.3 that could be reprogrammed.

Thanks,

Dan

[dantech]

Forget about v083 and v121. There were a few significiant software bugs (eg. in the digital filtering process). So there is no common sense to modify hardware for firmware with bugs.
There is huge difference between v08x and v12x. These are quite different programs. My releses are also quite different now.


Would you describe me damping resistors selecting process?

[baum7154]

[QUOTE=baum7154;220762]Perhaps I am referencing an earlier comment in your thread before the current V1.6.5, but still for a very fast 3DSS coil critical damping must be performed in order to get below 10us delay necessary to see very small gold as this small fast metal decays in well under 20us. Have you tried to detect the 6mm square of aluminum can side wall yet? I am anxious to try out your new firmware but don't have a setup for programing the Atmega chip. I do have a spare Atmega chip with the old V0.8.3 that could be reprogrammed.

Thanks,

______________________
dantech
I am sorry, the posts are very early on page 2 of your Polish thread starting at post #14 is a discussion of the ferrite but it is not relevant to version V1.6.5.

Dan

[baum7154]

Would you describe me damping resistors selecting process?[/QUOTE]
---------------------------------------------------------------------------------
The process requires an oscilloscope connected to the preamp output and set to display the coil discharge after the last pulse. There will be ringing on this discharge curve that can be eliminated by replacing the 390 ohm resistor R13 with one of proper value. To determine the proper value a network of 2-1200 ohm resistors and one 5k potentiometer is constructed and placed in place of the R13 resistor. The network looks like this: ___1200_______5k Pot_____.
----------------------------------------------------\________1200________/---------------------
In use the pot is adjusted to just eliminate the ringing as seen on the scope and the value of the network is measured. A resistance of that value is permanently installed as R13.

For a better explanation of this please see 'Making a Fast Pulse Induction Mono Coil' by Joseph J. Rogowski

Regards,

Dan

[dantech]

Thx,
I did quick test replacing 390 onto 1k ohm. The difference is only -2us. Detection range is the same.
I have to look onto oscilloscope

[baum7154]

Thx,
I did quick test replacing 390 onto 1k ohm. The difference is only -2us. Detection range is the same.
I have to look onto oscilloscope

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

Yes I have built the original coil and was not able to get it to any lower than a Guard Interval setting of 16. Since that time years ago I began building the 3DSS coils and they will go as low as 6us with a value of 328uh. It is quite possible that the 1000 ohms was too much damping resistance value for your coil. However I did just run some rough numbers and you might try R13 resistance values from 750 to 1500 ohms for your coil.

Thanks,

Dan

[dantech]

I was looking on the osciloscope and with 1k ringing was visible. 390 is good for dedicated coil