TGSL 2 tones ID

[ivconic]

Thanks!

[satdaveuk]

Thanks

[hugo]

Two videos of my MD.
The first one shows the detector working in "standard" mode : All metal followed by Disc mode.
The second one shows how the audio mod works : lower sound for ferrous, higher sound for non-ferrous.
I've done a small change from my last post : Pins 5 & 9 (CD4024) are always connected to Audio and the FET drives the pins 7 & 12.

http://www.youtube.com/watch?v=dgF0NR4JQq8

http://www.youtube.com/watch?v=R9_Sh9xk4L4

[simonbaker]

Two videos of my MD.
The first one shows the detector working in "standard" mode : All metal followed by Disc mode.
The second one shows how the audio mod works : lower sound for ferrous, higher sound for non-ferrous.
I've done a small change from my last post : Pins 5 & 9 (CD4024) are always connected to Audio and the FET drives the pins 7 & 12.

http://www.youtube.com/watch?v=dgF0NR4JQq8

http://www.youtube.com/watch?v=R9_Sh9xk4L4

Seems to work very nicely -- is there a region where certain metals make no beep at all?

If you can separate the tones more it would be easier to hear the difference.

Great idea and execution to make an improvement with very minimal changes.

Thanks!

-SB

[ivconic]

Nice thing!
It works smooth!
That idea can be exploited more.

[hugo]

@Simonbaker :
Until you switch in Audio disc mode, the MD works like any other TGSL.
When you are in Audio disc mode, every metals give a sound.
In fact, the "basic" tone is done by the two diodes always connected to the CD4024 (Pins 5 & 9). A soon as the comparator LM393 detects a non-ferrous metal, it drives the FET and connects two more diodes between the CD4024 and the audio stage given a higher pitch.
Every metal target is given at least a low freq. sound.

I agree, the difference between low and high tones is small.
Because of the basic design of the sound generator, it's difficult to give a higher tone by adding the CD4024 outputs.
I'll try to use both a P channel FET together with a N channel FET to cut the low frequencies and add the high ones.
Any idea is welcome !

Note : The difference between low and high tones is more audible in real.

[Jerry]

What I had been thinking about is stealing the entire IGSL audio circuit (Q5,5,7,8,D19, 20 and Q9) and putting it on a small board along with another LM358 to duplicate the signal path from U7a and U8a. Also using Ivconic's feed point from the 4024 and your connection to the TGSL GEB channel.

Only three connection points to the main board once you disable the old audio circuit.

Since i have been just thinking about it and did nothing about it, I did not say anything. You beat me to it with your idea. So I am just offering it up as another idea.

This would give one tone or the other just like IGSL but would not have the capabilities of the third combination tone.

more food for thought.

Jerry

[simonbaker]

Hi,
I've done what I've said in my previous post ... and it works !
Re-use the second half of U107 to drive the audio and re-route the outputs of U106 to select the audio tone.
Voila !

Hi hugo:

I may be mistaken, but when I look at your schematic, it appears to me that the "two-tone" switch position disconnects the connection between u106 and u107.

Can you check that? Am I just not seeing it right?

Regards,

-SB

PS - on studying it more, I see how the overall logic works OK, although maybe a little different chatter dynamics in two-tone mode than with basic TGSL.

[simonbaker]

What I had been thinking about is stealing the entire IGSL audio circuit (Q5,5,7,8,D19, 20 and Q9) and putting it on a small board along with another LM358 to duplicate the signal path from U7a and U8a. Also using Ivconic's feed point from the 4024 and your connection to the TGSL GEB channel.

Only three connection points to the main board once you disable the old audio circuit.

Since i have been just thinking about it and did nothing about it, I did not say anything. You beat me to it with your idea. So I am just offering it up as another idea.

This would give one tone or the other just like IGSL but would not have the capabilities of the third combination tone.

more food for thought.

Jerry

Yes he beat me to the implementation too (but what's new about that?).

My approach might be to change the logic of u106 to be an "OR" rather than "And". Then having each one select a tone. But hugo's technique works, although there may be a subtle change in the chatter filtering because the u106 output is not filtered by C25 and u107 in two-tone mode.

Actually, the most appealing approach is to use different tones when the disc channel goes negative or positive.


-SB

[Qiaozhi]

Actually, the most appealing approach is to use different tones when the disc channel goes negative or positive.

Do you remember the Rimatron 7MX that I turbocharged and also added two tone audio?

[hugo]

Hi Simon,
I agree U106 is not filtered anymore by C25 in two-tones mode.
But in this case, U106 is only used to switch between tones.
The most important part become U107b (filtered by C25 ).
One thing I've noticed : I've had to reduce the value of R39 in order to increase slightly the threshold voltage at pin 2 of U107 (It's not a true comparator and appears to be more sensitive).
Note 1 : I'm waiting for a P channel FET to continue my tests. I'll let you know.
Note 2 : There is a mistake in my last schematic, the FET is reversed (D <-> S)
Note 3 :

Actually, the most appealing approach is to use different tones when the disc channel goes negative or positive.

I'm septic about that. To me, the signal looks like a sort of fluctuating wave when a target is passing over the coil. The polarity of the signal is not clearly set.

[Qiaozhi]

Note 3 : I'm septic about that.

I don't know if that was a typo, or you have these English words mixed up ... but I suspect you meant to say "skeptical", not "septic". The word "septic" means that you are infected by disease. I hope not.

[hugo]

I don't know if that was a typo, or you have these English words mixed up ... but I suspect you meant to say "skeptical", not "septic". The word "septic" means that you are infected by disease. I hope not.

You're right !
I think it's a false cognates ! (From french to English).

[simonbaker]

Hi Simon,
I agree U106 is not filtered anymore by C25 in two-tones mode.
But in this case, U106 is only used to switch between tones.
The most important part become U107b (filtered by C25 ).
One thing I've noticed : I've had to reduce the value of R39 in order to increase slightly the threshold voltage at pin 2 of U107 (It's not a true comparator and appears to be more sensitive).
Note 1 : I'm waiting for a P channel FET to continue my tests. I'll let you know.
Note 2 : There is a mistake in my last schematic, the FET is reversed (D <-> S)
Note 3 : I'm septic about that. To me, the signal looks like a sort of fluctuating wave when a target is passing over the coil. The polarity of the signal is not clearly set.

But in this case, U106 is only used to switch between tones.

Yes, but the switching will be noisy -- so the second tone may break up more.

To me, the signal looks like a sort of fluctuating wave when a target is passing over the coil. The polarity of the signal is not clearly set.

You have a point, I didn't think it through well enough. A typical target has a negative-positive-negative pulse. A discriminated target would be the inversion of that. So clearly can't just go by polarity. Also, targets at the exact DISC phase would make no pulse at all.

So it would involve more parts to do it right I think. Maybe have an inverted GB signal and another dual comparator to detect the inverted DISC channel. Now we could have "three" tones - one for GB channel, one for inverted DISC signal, one for normal DISC signal. The would be mixed together. Special case when only GB tone is present, it means metals very close to DISC phase, because neither DISC tone would sound.

Worth it? Probably not, but experiments are fun. Maybe another easier way to do it is out there.

Hugo's circuit is very good mod - simple enough and good enough.

-SB

[Jerry]

Worth it? Probably not, but experiments are fun. Maybe another easier way to do it is out there.

That pretty well sums up the hobby.

Jerry