New Idea

thank-you wm6 I did not have the link for carl 


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Johnny.
A lot of questions but I will address them all. (not in order)
Question 1. clock oscillator module. ECS100ax 4 MHz
Question 3. Coil is concentric 8 inch outer RX and 6 inch inner TX - #22 enamel Use enough windings on bigger coil to equal inductance of the smaller one. Possibly 25-30 turns on secondary about 390-400 µH
Question 2. Both resistor values should be determined separately using a scope and 500Ω 1W pot in series with 470Ω 1W resistor. Do not hook anything to secondary when making this setup. Adjust pot for least amount of ringing.
Question 4. I used Sony 8Ω lightweight stereo headphones. Not sure if piezoelectric will work. The signal level is 5 volts square wave.
Question 5. I would choose for the meter to swing left for non-ferrous and vice-versa for ferrous. I prefer not to use a meter, so I can concentrate more on where I am walking. Lots of rattlesnakes, holes, boulders and what-not here in the Arizona desert
I hope this helps you somewhat. Good luck

Posted on: May 21, 2014, 02:02:27 pm

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Johnny,
From your post I gather what you are suggesting is the idea of changing the fixed oscillator to match the tunable oscillator that is being disturbed by ground mineralization is what you are calling ground balance. This stirs up a lot of questions in my mind.
1. If you are adjusting the fixed oscillator, then is it not a fixed oscillator anymore?
2. What about using shielding on the coil instead?
3. How about using the micro to monitor both frequencies and some software algorithm to measure when the frequencies have been disturbed by metal and not ground balance problems?

I do not want to discourage you from trying your ideas in any way. Great inventions have been made by people who refused to believe "It can't be done". We always brag about our successes, but not our failures even though the failures are what led us to success.
Let me know how it works out.
Again thank you for your link to that article.
golddustcarl

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A bad day at gold prospecting or metal detecting is better than a good day at work.

6666
 No I did not get an e-mail recently. I used audio coax salvaged from an old pair of audio cables I had laying around. They were each about 1/4" shielded coax, molded and flexible. Don't know the impedance, probably 75 ohms. Cut the ends off and soldered one end directly to coil wires and the other end I used 2 DC power plugs and matching chassis mtng. jacks. Inside I connected the jacks to the board with separate Amphenol plug and jack assemblies so that I could remove the board easily. Same things for  controls and jacks.
Nickels are harder to detect than copper or silver coins. American nickels are an alloy made of 25% nickel and 75% copper except nickels made during WWII (1942-1945  56% copper,35% silver,9% manganese). The best I got was about 3 inches inches open air. Copper, gold and silver faired much better. A 1922 silver dollar at 10 inches. Nickel has a higher resistivity. If they took the nickel out of them and made them all copper you could detect them farther away.
golddustcarl
 
golddustcarl

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A bad day at gold prospecting or metal detecting is better than a good day at work.

WM6
Yes, you should be able to do that, but not a view meter as they are not linear. Try a standard 0-2 ma and set the no target voltage reading to 1 ma. That way as the voltage drops, it will swing downward and go upward as the voltage increases.
Iron will increase the voltage, and non-ferrous will decrease the voltage. It would be wise to mark the chassis behind the knob for the first comparator where the 12 µS and 18 µS spots are. that will help you later when you try to use it.
Hope this helps.
golddustcarl

Posted on: May 22, 2014, 06:27:01 pm

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wm6
Forgot to mention that most view meters are not 0-1-ma. most are in the µa range.
golddustcarl

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A bad day at gold prospecting or metal detecting is better than a good day at work.

Hi golddustcarl

those 1k PTK thermistor  should be mount at NTE2987 body, or it is for compensate inner box temperature only?

Thanks
WM6

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