Audio

[Qiaozhi]

Discussions related to the design of the audio section.

[green]

What is the most desirable audio response?

[kt315]

What is the most desirable audio response?

a hight pitch on a gold. only on a gold. an aluminium let be reacting by low tone. is it OK?

[soverey]

a hight pitch on a gold. only on a gold. an aluminium let be reacting by low tone. is it OK?

Does this imply that the detector will have some sort of discrimination based on the conductivity of the metal? .... personally I like the audio of the Dooley's TD3X , similar to the Minelab's pi detectors.

[Teleno]

Apparently XP detectors have asked themselves same question and had some experienced detectorists involved in the development of their audio.

Perhaps the owner of an XP can tell us what that audio is.

[WM6]

. personally I like the audio of the Dooley's TD3X , similar to the Minelab's pi detectors.

I consider Minelabs PI audio most awful possible:

https://youtu.be/CL9oEs1BG7w

[Monolith]

I consider Minelabs PI audio most awful possible:

https://youtu.be/CL9oEs1BG7w

If the audio signal is to be continuous, it should be of a very low pitch. A change of pitch is easy to discern.
Variable pitch together with variable volume would be best.

Seasoned detectorists can pick up a lot of information from a good audio. For a beginner, just beep beep is good enough.

[WM6]

Kojak sirene like hearing torture has nothing to do with collecting useful information out of good audio signal.

If it is 5min in question, OK, but all days of detecting under such psychedelic voice someone must go crazy.

[ivconic]

If we talk about real improvements... than i will mention again Doley's idea and how he done it at TD3X.
That's the audio i would like to hear on Surfmaster II too.

[Old cart]

Smooth audio seems to be a characteristic of using optoisolators in the signal path as they have an inherently filtered quality and isolate the audio section from small noise spikes.

[Old cart]

I have also though of using stereo headphones. Each ear cup would be fed a different signal. For example with two detection channels one could be tuned for low conductivity, one for maximum iron response. The channels would NOT be combined and each would have it's own audio path. The brain would then learn the signature for iron so that the user could learn to either tune of or seek iron depending upon whether you are beach detecting looking for rings or relic hunting.
And no loss of depth due to subtractive effects!

[mickstv]

Here's the audio circuit I use for all my Ground Balancing PI detectors. It's designed to work on detectors that use a Nch Mosfet for the TX.

The input capacitor 2.2uf, depending on target time constant sees a varying voltage +/-5 volts from the previous integrator stage, IC10A amplifies that signal. IC10B changes the varying voltage too, all targets going to +5v. IC11A is a buffer so as the previous stage doesn't get loaded down. IC11B is basically threshold control.

The CD4046 produces a varying pitch dependent on target time constant. The amount of variation is limited by the two led's.

So the output audio is varying pitch plus no or low output until the target breaks through the threshold level then the volume increases the closer the target gets.

[Old cart]

Here's the audio circuit I use for all my Ground Balancing PI detectors. It's designed to work on detectors that use a Nch Mosfet for the TX.

That looks like a very nice design. Does the 4046 output sine waves? Is this all the circuitry after the integrator? If so you could make a very nice smooth sounding VCO audio by using a LDR based attenuator following the 4046 and then have it drive the speaker/ headphones directly via a power amp like the LM386.
Also by using low offset precision quad op amps you do this with only two chips and eliminate the offset adjust.

[Jose]

Hello Mickstv
Thanks for posting this scheme two audio tones.
I have a question.
IC10B, has the mission to always deliver positive voltages, even if their entry, tensions may be of negative value, or positive.
According to the scheme, IC10B settings, respond well when the voltage at its inverting input is "negative" polarity.
I do not understand, is how this scheme responds when Intlet tension is positive, since it is inverted (negative value) in the Katodo, BAT85 diode, being tension, is blocked.
Thank you
Jose

[mickstv]

Hi Jose, here's a link with the same circuit shown. It definitely works.

Link below

http://www.linear.com/solutions/1608