The Audio

[ivconic]

iveconic,

I am so sorry, the circuit that I posted is a working draft with lots of mistakes specially in the audio part.
I got the audio working on the breadboard. A bit later today I will update the posted circuit to the working level.

Please tell me about the parts that you can not get and I will look for alternatives. My own parts have to 90% been sitting in my box for over 20 years.

Tinkerer

So far only LF398. I searched databases of local suppliers. One has it in database but not on stock.

[ivconic]

ivconic,

attached is the circuit with some changes, including the values of the capacitors.
Pin 5 on the CD4046, is the INHIBIT pin. When it is high, the VCO has no output.
The threshold is set with R33 and R37, that set the hysteresis on the comparators IC13A and B. I will change the IC's 13A and B to dedicated comparators when I get hold of the comparators.
Tinkerer

Thank You very much! I will correct those at my testing board.
Regards!

[Tinkerer]

So far only LF398. I searched databases of local suppliers. One has it in database but not on stock.

The LF398is a Sample and Hold amplifier. LF198 and LF298 or NE5537 are all about the same. I think most Sample and Hold amplifiers with external capacitor can be used.
Tinkerer

[Teemo]

At the end we need to convert the signal into something that the operator of the metal detector can capture with his senses.
The primary option is audio.
-We want two different tones, one for magnetic targets and one for non magnetic targets.Then we want to have a variable pitch or frequency for each tone, so that the operator can discern minute differences in target response and gather information from it.Then we might want to have an increase in volume as well as a difference in pitch, to indicate targets.Next we have to make a choice of sound quality. A square wave output hurts the ears, a sine wave sounds great, but takes a lot of processing, probably, somewhere between would be a good compromise. Earphones sound great and use little power, they also exclude external noise, however, lots of people prefer a loudspeaker. This needs to be quite powerful to compete with environmental noise and wind in the ears.

Personally I prefer sound at below 1khz so my present circuit uses a VCO with a center frequency of about 500hz, going up for gold and down for iron.

Presently I will post my draft circuit. It functions but is very far from perfect.
I hope more knowledgeable people will jump in and help developing a good audio.

Ah, and not to forget, the timing of the TINKERERS V1 is done with a PIC MCU. this could also produce the sound.

Tinkerer

Hi!
This is all very well said about the audio. Have you made any progress recently on getting audio directly from PIC?

[Tinkerer]

Hi!
This is all very well said about the audio. Have you made any progress recently on getting audio directly from PIC?

Unfortunately, my skill in programming is very minimal.

[Pete the Builder]

Would a polyphonic synthesised source be easier to use to perform "audio discrimination", or is that overkill? If so, perhaps a second-harmonic (or even-harmonic) generator could be useful?

Mixing different (even) harmonics can even help those with hearing difficulties, such as tinnitus or severe hearing loss. Perhaps also a hearing aid driver might be useful? I may be able to help out in some small way, as long as I'm not standing on anyone's toes!

-Pete

[Tinkerer]

Would a polyphonic synthesised source be easier to use to perform "audio discrimination", or is that overkill? If so, perhaps a second-harmonic (or even-harmonic) generator could be useful?

Mixing different (even) harmonics can even help those with hearing difficulties, such as tinnitus or severe hearing loss. Perhaps also a hearing aid driver might be useful? I may be able to help out in some small way, as long as I'm not standing on anyone's toes!

-Pete

All Tinkerer's circuits are fully open source. Anybody and everybody is very welcome to make improvements and post them here.

Any kind help is much welcome.

Tinkerer

[Teemo]

Would a polyphonic synthesised source be easier to use to perform "audio discrimination", or is that overkill? If so, perhaps a second-harmonic (or even-harmonic) generator could be useful?

Mixing different (even) harmonics can even help those with hearing difficulties, such as tinnitus or severe hearing loss. Perhaps also a hearing aid driver might be useful? I may be able to help out in some small way, as long as I'm not standing on anyone's toes!

-Pete

Polyphonic synthezised sound would be the best I guess. But do you have ideas how to generate this with 8bit PIC.

It is suprising how many people actually have hearing problems. They do well in everyday life, and hear human speech well, but when you play them even single 1 kHz signal they can't hear it or hear wery badly. So it is certainly the thing to think about -- how to make the sound easier to hear.

[Pete the Builder]

I'm playing with a dual PWM channel idea at the moment. My C is a bit rusty, though. An alternative might be a simple top octave synthesizer with second harmonics mixed in. I'll try a couple of things on my Arduino Due and get back to you before the weekend.

i have severe (56dB+) bilateral tinnitus from my constant pain medication. Luckily it's in the "cricket" or "cicada" range, so anything below about 4kHz is best, both for me and age-related or industrial hearing loss in general. It might be helpful to offer an option to change the overall audio range, to allow anyone to select what's most comfortable for themselves. But it must be simple! Hmmmm....

[Tinkerer]

I'm playing with a dual PWM channel idea at the moment. My C is a bit rusty, though. An alternative might be a simple top octave synthesizer with second harmonics mixed in. I'll try a couple of things on my Arduino Due and get back to you before the weekend.

i have severe (56dB+) bilateral tinnitus from my constant pain medication. Luckily it's in the "cricket" or "cicada" range, so anything below about 4kHz is best, both for me and age-related or industrial hearing loss in general. It might be helpful to offer an option to change the overall audio range, to allow anyone to select what's most comfortable for themselves. But it must be simple! Hmmmm....

Maybe you want to have a look at the complete project thread. A few members want to have a go at the Tinkerers_SB_MO detector. The weakest part of this design, is the audio.

With your help we might be able to improve that a lot.

Tinkerer

[Pete the Builder]

I did 'sample' the thread, but stopped after the first few pages... I've just started a brand-new pain medication, and it takes a huge effort to concentrate on anything right now... It's doing my head in! But I'll go through the thread later tonight if I can, and see if there's anything I might be able to help with in any small way.
Thanks for the suggestion!
-Pete

[Tinkerer]

I did 'sample' the thread, but stopped after the first few pages... I've just started a brand-new pain medication, and it takes a huge effort to concentrate on anything right now... It's doing my head in! But I'll go through the thread later tonight if I can, and see if there's anything I might be able to help with in any small way.
Thanks for the suggestion!
-Pete

Let's see if we can take a shortcut then.

Maybe we could start with the following:

The Tinkeres are discriminating designs. The input to the audio, is basically a varying DC voltage.
With ferrous targets the voltage goes towards negative and with non magnetic targets the voltage goes towards the positive direction.
I would like to have one or more proportional audio tones that let the operator recognize the kind of target under the coil.

all the best

Tinkerer

[Davor]

I'm playing with a dual PWM channel idea at the moment.

remember that XOR-ing the two PWM-s wil give you a multiplication of waveforms they represent.

[Pete the Builder]

My cats do not like me at the moment.

I can't say I blame them!

Any audible combination of 2 PWMs sounded pretty awful, except for obvious tunings (half, third, etc), but those were also a bit harsh, even with filtering and gating. They kinda sounded OK on the bench a couple of times, but when I routed them to a reasonable set of headphones, there's no way you could listen to that for hours.

But using them purely as notification tones - "ooh, there's a huge nugget of gold/tin bucket/water pipe/stash of doubloons", the results re actually pretty darn good!

i haven't "functionalised" the code (I'm still figuring out Arduino coding), but there's no reason why this couldn't be used in a real world unit. Heck, it's not that hard to write it in assembler - I just need to quickly init the two PWMs to the right frequencies and duty cycle (which can be changed to suit different headphone types, by the way!), then enable them for x milliseconds or until the detection algorithm says the target's gone! And we can even 'ramp up' the duty at start and finish to emulate a fade! I surprised even myself with this idea...

I'm trying some new painkillers so my "lucid time" is a bit limited at the present, but when I get the code into a modular format, I'll be glad to post it here.

oh, and using more PWMs makes for more melody. If we had unlimited resources, we could make the thing sound like an orchestra...

I hope this gives you something positive!

Oh, and thanks for the tip about xoring... I didn't even consider that option. Makes a bit of a mess, though.

cheers,
PtB

[Tinkerer]

My cats do not like me at the moment.

I can't say I blame them!

Any audible combination of 2 PWMs sounded pretty awful, except for obvious tunings (half, third, etc), but those were also a bit harsh, even with filtering and gating. They kinda sounded OK on the bench a couple of times, but when I routed them to a reasonable set of headphones, there's no way you could listen to that for hours.

But using them purely as notification tones - "ooh, there's a huge nugget of gold/tin bucket/water pipe/stash of doubloons", the results re actually pretty darn good!

i haven't "functionalised" the code (I'm still figuring out Arduino coding), but there's no reason why this couldn't be used in a real world unit. Heck, it's not that hard to write it in assembler - I just need to quickly init the two PWMs to the right frequencies and duty cycle (which can be changed to suit different headphone types, by the way!), then enable them for x milliseconds or until the detection algorithm says the target's gone! And we can even 'ramp up' the duty at start and finish to emulate a fade! I surprised even myself with this idea...

I'm trying some new painkillers so my "lucid time" is a bit limited at the present, but when I get the code into a modular format, I'll be glad to post it here.

oh, and using more PWMs makes for more melody. If we had unlimited resources, we could make the thing sound like an orchestra...

I hope this gives you something positive!

Oh, and thanks for the tip about xoring... I didn't even consider that option. Makes a bit of a mess, though.

cheers,
PtB

Thanks for the feedback.
sound like an orchestra... Years ago I was thinking about a multi sound output for the detector. I was going to call it "Harmony". Just too complicated in analog.
Amazing what a clever mind in the digital world can do nowadays. Great job!

Different headphones. Yes, this is one of the problems I run into when experimenting with the audio. Depending on the dynamics of the speaker, sometimes it sounded OK and other times not.

For a continuous background audio, good to have so one knows the detector is working, a just barely audible soft frequency would be fine. Then a target indicator that can be attention calling.

The ferrous tone more remote, as we do not really want to find iron junk, just know it is there.

Important is the fast response. We want to know that the target is there, when it is under the coil, not some time later. At a sweep speed of about 1 meter /second, this means a lag of not more than 10cm or 100ms.

Thanks for the good work.

All the best

Tinkerer