What is this signal from the audio output

[wyndham]

I have been reading all the different post for mods and i understand what we have is a filtering and amp system from front end to back.
I read a post on another forum of someone who , using a PI(no idea which) picked up a faint signal and 20" later had a beautiful crystalline leafy Rye Patch nugget.
With every thing said and done all we get is a signal to either headphones or speaker from the amp system in the PI no matter how complicated the PI box is.
What is the signal strength from th PI's output or put another way is what is the threshold thatyou have to have to "Hear" thru the head phones. Is it 1volt or .1 or less and even though, this may sound simple to those that build and design machines but my hearing is the weakest link in this chain.
How about a LED bar with an amp split off from the output that shows the signal but it can have a greater gain and filter than the ear could tolarate.
Maybe this already is in use and I'm not up to speed on whats out there.
It could be a PIC microcontroller that's sole funtion is to filter and amp the signal to the LED.
Wyndham

[Carl-NC]

Hi Wyndham,

It's not so easy as a voltage strength. Different speakers/headphones have different impedances & efficiencies, so to get the same threshold level might require different voltage (actually power) levels. Add to that variations in human hearing, where one person's audible threshold is another person's silence.

What you are actually interested in is the minimum audible shift. That is, once you have an audible threshold set, what is the weakest variation you can distinguish? I don't know the answer to that. But it turns out that most people are more sensitive to variations in frequency than variations in loudness, so a VCO-type audio is generally a better choice.

Also, I have some old 70's detectors with the simple signal strength meter, and I've noticed that quite often the meter will deflect on a deep target even though I can't hear any audio shift. I don't know if this suggests that meters are a more sensitive indicator, or if the audio was intentionally "toned down". Heh.

You are right, that were dealing with filters and gain, and you might think that just adding more gain will add more depth, or sensitivity, or whatever. But you also have noise and interferers coming in, and they are difficult to eliminate. So adding more gain almost always increases false signals.

- Carl

[Unregistered]

Adding filter also causes decay of signal. Where is compromise?

[wyndham]

So if we use the strength comming from the output fed into a meter or led or input for a microcontroller, if a known target gave a known output then shouldn't that give a baseline.
Eric did an air test of a wire loop(single loop)
"The sensing coil would have to be damped to stop it ringing and ideally one turn to simulate a target. Using a 1in diameter one turn coil with a 10 ohms resistor across it, I get 1.5mV at switch off 0.5m above an 8in coil in air, when powered by a GS5. "
Would this be a valid starting point to see if a better reciever or signal enhancer can be found? Are there other factors that I've missed?
Wyndham

[Reg]

Hi Wyndham,

I am not sure just what the 1" diameter loop simulates, but you can do the same thing using known or a series of consistent targets. You could use simple coins such as a dime, a nickel and maybe a half dollar to give you three sizes and two conductivities. When changes are made, they may alter targets differently, depending upon the change.

So, you might want to include a low conductor, a medium conductor and a high conductor as well as different target sizes if you want a thorough evaluation of your changes.

If you are just focusing on a particular target such as gold nuggets, then a range of similar objects could be used. I would still test other conductive objects just to see what happens with them also.

Now, the key to any evaluation is consistency so you should try to use some fixed device to assure the same distance. This could be some adjustable mechanism or as basic as simple solid boxes as spacers between the coil and the target.

At least, that is what I would do if I was looking for a thorough idea of what a mod did.

Now, one more important thing, have fun with your testing.

Reg

[wyndham]

Thanks Reg, the post on Eric's forum was in simalar nature to create a constant baseline target where air test seem to leave out some of the varibles of the different types of soil conditions.
I had mentioned the idea of placing a coil of a certain size at a known depth with a known voltage so that one could measure a RX signal from a known source in ground.
As some of you who have seen my post on this and other forums, I'm a bit of a squirrel, jumping from one idea to the next.
Reg, I posted an observation and offer to make you some clay w iron oxide targets on the White PI thread on NH. I , as a squirrel, may well be looking for a hickory nut in a peanut patch but some of what seems to me, is there maybe a difference in the construction of iron in (rock, clay,pottery, etc) than non ferrous metals so that the resulting RX signals we get may have a unique and different magnetic signature from the other non ferrous metal. Gold being highly diamagnetic, seems to say there maybe a uniqueness to gold that could prove valuble in PI detecting. There again my lack of training in electronics theory and practical, may lead me in well over my head, but at least squirrels can run up a tree when the water gets too deep .
And yes having fun with all this is really whay it's about. A hundred years from now, I have a feeling, we will be doing something else
Later Wyndham