chance pi build

[green]

.[ Has anyone built a similar two stage op-amp using two of the OP37 chips and a nominal +12V & -12V supply?]

The answer is no but I would try a simple modification to what is there. If it works then add the second stage. Using the input resistor as R damping saves a couple of usec. Remove R13, add diode across R25, change R25 to 20k, adjust R16 for R damping.

[baum7154]

Did a bit more scope time in the CHANCE PI with an 8" fast spider coil today. Measured the time it takes for the OP37 to come out of saturation on the flyback signal at various gain settings. The coil itself measured at the protection diodes decays in 6us. With the designed gain of 470 the OP37 amp takes right at 16us to come out of saturation and smoothly back to zero with proper damping. Dropping the gain to 43 the amp settles to zero in 8us. Further dropping the gain to 21 allows the amp to settle to zero in about 6us, virtually the same as the coil itself. I took pictures of these test measurements for future reference.

I intend to build a 2 stage op amp, 1st stage inverting with a gain of 20 to 25, and the 2nd stage non-inverting with a gain of 20 to 25 to allow better/faster sampling for small gold targets. Has anyone built a similar two stage op-amp using two of the OP37 chips and a nominal +12V & -12V supply? No sense re-inventing a good wheel!

I appreciate any responses.

Dan

[baum7154]

Beautiful picture of Waikiki and Diamond Head. I miss snorkeling at Hanauma Bay!, but not the Lion fish I met there!

[Waikiki_Sweep]

Yes I was wondering why you were trying to move your coil in water at 5ft/sec with CHANCE PI in your discussion on hydrodynamic drag.

Because of size of the area.
After government replenished sand on the beach and then sand has been washed back to the ocean
submerged sandy area has increased three times over that you can see on this picture:
It was huge. Now it is endless. Also number of tourists has decreased several times.
So now I am walking over several football fields finding only few targets. With speed 1ft/sec I will find one penny a day. I wish I cal fly.

One Italian guy has searched that area with Whites Dualfiend for 90 days day by day to find only three silver rings this winter.
Problem was that he can only push that bulky coil forward, he can not swing it in water because of huge drag. As result 0.05% of area has been searched.

I remember the time when real gold rush was here. Now I am practically go outside for exercising and listening music with MP3 player installed into my Surf PI waterproof box.
Some good stuff probably remains in corals but I need a target id machine (Chance?) to dig from corals only good targets.

[baum7154]

Yes I was wondering why you were trying to move your coil in water at 5ft/sec with CHANCE PI in your discussion on hydrodynamic drag.

Yes the low tone is the same as for a gold ring or small piece of aluminum. The low tone for iron nails happens for me too at low signal levels but as the signal level increases the discrimination becomes more defined and the melody tones begin for copper, silver, and iron at the right end of the VDI scale.

The very low tone you see with large Iron targets is raspy and lower than the low tone for gold and aluminum. That very low tone indicates signal strength is saturated or overloaded.

Regards,

Dan

[Waikiki_Sweep]

Thank you! Now I have a data for comparison.
For my tests with longer delay (Guard Interval) results are more stable.
Looks like my Chance works properly because it shows similar behavior.

Also I see Chance is not a "motion detector". I have a habit to swing target near coil after years of use of Surf PI.
With Chance you can just keep a target near coil and get the tone. Shaking target makes things only worse.

That tone you call "low" is the same tone you have for gold ring? Because in my case I have a low tone for gold rings is same as for iron nails.
For very big iron targets (screw-bolt) I have a "very low" tone sometimes. May be it is iron signal or overload signal. Too bad author has left no notes.

[baum7154]

I'll try to answer your question the best I can. With my 8" 335uh spider coil and the Guard Interval set to 10, a 12 penny iron nail pointing directly at the coil gives a high pitched tone much like the response to silver. The same nail presented broadside to the coil gives a low tone at greatest detection distance and as the nail gets closer and the signal strength gets stronger, discrimination kicks in and the melodious high pitched tones begin. The right hand end of the VDI is correlated to the high tones and this includes copper, silver, and iron. The left end of the VDI is where the low tone is allocated and this is where gold, aluminum and nickel reside. Saturation of the Signal Strength level gives a raspy buzz.

I also tried different Guard Intervals to see what effect they had on audio response. The same nail target was used.

GUARD INTERVAL-----END ON TO COIL---------------------------------------BROADSIDE TO COIL

12-----------------------8" low tone, 7" musical, 5" solid high tone------------8" low tone, 4" musical notes begin

15-----------------------8" low tone, 6.5" musical, 5" solid high tone----------8" low tone, 3.5" musical

20-----------------------8" low tone, 6.5" musical, 5" solid high tone----------7" low tone, 3" musical

30-----------------------8" low tone, 6.5" musical, 5" solid high tone----------6" low tone, 2.5" musical

So to answer your question both very high pitch and musical audio can represent Iron depending upon target shape and orientation to the coil. It is interesting that there is a musical transition from solid low tone, to musical, to solid high pitch tone when the target is presented 'End On' to the coil.

I hope this helps.

Dan

CORRECTION
The nail used in the above test was an 8D, NOT a 12 penny nail. Sorry for the confusion.

Dan

[baum7154]

I'll try to answer your question the best I can. With my 8" 335uh spider coil and the Guard Interval set to 10, a 12 penny iron nail pointing directly at the coil gives a high pitched tone much like the response to silver. The same nail presented broadside to the coil gives a low tone at greatest detection distance and as the nail gets closer and the signal strength gets stronger, discrimination kicks in and the melodious high pitched tones begin. The right hand end of the VDI is correlated to the high tones and this includes copper, silver, and iron. The left end of the VDI is where the low tone is allocated and this is where gold, aluminum and nickel reside. Saturation of the Signal Strength level gives a raspy buzz.

I also tried different Guard Intervals to see what effect they had on audio response. The same nail target was used.

GUARD INTERVAL-----END ON TO COIL---------------------------------------BROADSIDE TO COIL

12-----------------------8" low tone, 7" musical, 5" solid high tone------------8" low tone, 4" musical notes begin

15-----------------------8" low tone, 6.5" musical, 5" solid high tone----------8" low tone, 3.5" musical

20-----------------------8" low tone, 6.5" musical, 5" solid high tone----------7" low tone, 3" musical

30-----------------------8" low tone, 6.5" musical, 5" solid high tone----------6" low tone, 2.5" musical

So to answer your question both very high pitch and musical audio can represent Iron depending upon target shape and orientation to the coil. It is interesting that there is a musical transition from solid low tone, to musical, to solid high pitch tone when the target is presented 'End On' to the coil.

I hope this helps.

Dan

[Waikiki_Sweep]

Who can tell how Chance identifying ferric targets?

What sound tone you have on iron pieces with your properly adjusted Chance?

With different coil inductance I can see some changes in target identification:

coil inductance --- 400 uH --- 300 uH
cooper coins --- high tone --- high tone
Au,Al,Ni --- middle tone --- middle tone
Ferric targets --- middle tone --- music box sound

Because no instructions I have no idea what that music "cannery bell" sound has to indicate? Is this Iron ID? Can you confirm?
If so, that is good because I want to get rid of iron trash. And lower inductance coil may help to adjust identification.
400 uH coil works bad because gold and iron sound is same.

Those modes of iron rejection 2,3 reducing not only iron but gold rings signals too.

I have tried different coils. Inductance makes a difference in target IDs.
Any shape can be used and for "slow" high capacitance coils guard interval has to be increased but sure platinum and some gold goes undetected if so.

I have no idea is my Chance works right or wrong. That is only what I can see.

[Waikiki_Sweep]

If your computer in new probably you will see no serial port in it so you need to buy or build USB programmer.

For older computers with serial port "3 RESISTORS" AVR programmer keeps a record of cheapest of the cheapest : http://www.electroons.com/electroons/programmers.html

[STAVROSNU]

I use the same as Silver Dollar and is perfect. It costs nothing and works super !

[Waikiki_Sweep]

Also if you like to save $3 you can build your own USB programmer for your AVR microcontrollers using cheap 8 pin Attiny 45 or 85: http://www.simpleavr.com/avr/vusbtiny

[greylourie]

I have used USB programmer for AVR. You can find it on eBay starting $3. Name is USBASP. http://www.ebay.com/sch/i.html?_nkw=USBASP
Also there is a very simple software to use with it - Khazma AVR programmer. http://khazama.com/project/programmer/

But please pay attention for fuses because for Khazma checked bits = 1 but on Chance website with Ponyprog screenshot it has checked bits = 0

So INVERT ALL FUSE BITS or Ooooopppssss.... Atmega8 Bricked.....

Also write codes first than fuses so if you mess up with fuses you will have at least codes ready to go.

Usbasp works well with eXtreme Burner-AVR software. Find it here : http://www.fischl.de/usbasp/ . Works fine on Win7. Used it for programming open source stuff on a Turnigy 9x. Also reprogramming my generic Lipo charger. Theres an online fusebit calculator here : http://www.engbedded.com/fusecalc/ . Where you can double check before programming. Important for a nub like me.

[Silver Dollar]

Here's the schematic to the parallel port programmer;



The buffer chip runs off the power in the board to be programmed so the problem
is the MISO signal that is buffered on pin 9 of the chip is a CMOS signal at the voltage of
the board to be programmed. Normally pin 9 goes to pin10 on the connector through a resistor
so I made up the level translator using a transistor, the problem is I have to get 5V somewhere
to make the computer happy. I'm not sure if the programming software keeps any lines high
that I can use.

They had trouble with USB programmers at work so have standardized the parallel port type.

I saw those USB ones and figured they are just a serial emulator but wasn't sure what software to use
with it. I also have a low budget so free is better than even $3...

[sinclairuser]

silverdollar, sometimes between different computers you can have problems with the 3v in the paralell port, there is a workaroud where you isolate the voltage from the computer and provide the voltage separately to the programmer, though i have not done this, i switched to serial and then usb ages ago.
i think the separate power helps when using different machines, as some pc's have no power pin or different pins for power, there are those who prefer paralell programing, another thing to check is port mode in the pc's bios(sounds obvious but can be forgotten).