complete project

[Tinkerer]

Hi Tinkerer,
Nothing like an image or a schematic to get the theory across. Thank you.

I've been thinking about the audio and believe that the volume and frequency should increase relative to target strength. I don't think the clicking bone type is responsive enough, nor is the simple volume increase, but the two combined creates a strong impression.

I was looking at the raw Rx signal before filtering and was wondering what would happen if this was synchronously demodulated with a precision high speed PLL chip? The result maybe a very interesting decay curve which when sampled at 2 or 3 points could provide some extra information about the target. At least it should provide a consistent almost noise free signal.

I'm ashamed to say I've not built the 12V frontend you posted yet, and it's so simple too....next week I hope. I've got some PLL chips kicking around somewhere among my bits too. Tomorrow I'll have a hunt for some high voltage caps among my junk.

All the very best
Kev.

Hi Kev,

thanks for the feedback.

I agree with you that a good audio can make a big difference in the detecting.
We want a fast response detector. For a 40cm coil, motion detector, the response should be about 100ms. That is, we want to hear that nugget within 10cm of sweep. Considering a sweep speed standard of 1m/s.
For a non motion detector the sweep speed can be considered quite a bit lower. The response can then be slower too.
A slow response means we can integrate more samples for better S/N.

Ear phones or bone conductors can click. For a fast response the minimum click speed would need to be about 15Hz. But the clicking does not work well with loudspeakers.

The human ear has some quirks that need to be taken into account. We can easily hear a difference in frequency, but a relative large increase in loudness is needed to be distinguishable.

Then we need to consider the annoyance of a continuous sound, yet, if we hear no sound at all, we worry that the detector does not function.

What is a good minimum frequency? 600 to 800Hz? A square wave makes a very harsh sound. This can be softened with a LP filter. A sine wave needs more power to be heard.

A piezoelectric element is very power efficient, but makes a horrible sound.

How loud does the speaker need to be? If there is wind then the speaker needs to be quite loud. On the other hand, the modern earphones are capable of beautiful sound at low power.

One frequency?
2 frequencies? High-low?

I really know very little about making a good audio for a detector. Some help would be greatly appreciated.

You were looking at the RX signal.... could you give me a link to what you were looking at? I have posted so many scope pictures and simulations, I am lost in the maze.

I can show the raw, unfiltered signals of large targets on the scope, but for small target behavior it is better to look at a simulation.

How do you feel about a 40cm diameter coil? I think it would come close to your needs.

All the best

Tinkerer

[satdaveuk]

Hi
Its looking good and have gone such along way in short time
Has anybody made any lay files for this project yet ? or am i been cheeky/lazy
Serious level taking my hat off to you Moodz and everyone else on here who has worked so hard on a bespoke design such as this.

Regards

[Tinkerer]

Hi
Its looking good and have gone such along way in short time
Has anybody made any lay files for this project yet ? or am i been cheeky/lazy
Serious level taking my hat off to you Moodz and everyone else on here who has worked so hard on a bespoke design such as this.

Regards

Thank you for your kind words, Dave.

Below is an older circuit and board. There are some good things in that circuit, but others could use some improvements. For example the Audio. The response is not dynamic enough.
The use of the CD4046 could be much improved.

Tinkerer

[6666]

Tinkerer is there a high resolution version of your schematic available anywhere please ?

[Tinkerer]

Tinkerer is there a high resolution version of your schematic available anywhere please ?

I think at the post below, is the last version. EAGLE FILES.
I do not recommend to build it. I posted it for discussing it's good and not so good parts.
We might re-use some parts in the TINKERERS_TEM_IB-PI.

For example the 2 tone audio (needs improvement) with the mute and dead band.

http://www.geotech1.com/forums/showp...24&postcount=6

Enjoy

Tinkerer

[Tinkerer]

No help?

No ideas?

Well, so I must put on my own thinking cap. Watch out for the smoke!

Going back to the audio:

The VCO of the CD4046 gives about one decade of frequency variation. We could use it from about 100Hz to 1100Hz and making the 0V at about 300Hz. This leaves a larger pitch variation for the gold, positive going, and a smaller variation for the iron, negative going.

300Hz is also easy on the ear, for a continuous sound, indicating the proper function of the detector and also indicating slow, small variations in the ground response.

We will also LP filter the 50% duty cycle square wave, to make the sound less harsh.

The problem is now, how to make this pitch variation non linear.

We want a fast response to minute targets. Large or very close targets give such a strong response that it will saturate everything in reach.

A log amplifier seems to be the answer. This will give a relatively larger change in pitch for the small targets.

The CD4046 also has a mute pin. This is useful for the switch ON time where many detectors scream at maximum ear shattering volume.

OK so let's draw up a circuit and test it.

What about the increase in volume? This is another wish on the list. A target should produce a change in pitch and also an increase in volume. So this is the next problem to solve.

Any suggestions?

Tinkerer

[satdaveuk]

Hi Tinker
The DFX Whites circuit would be perfect for the increase in sound , problem is i dont have it..... unless you want me to dismantal mine to have a peek?? and do a bit of reverse
You realize though thats my babe the bees, goes places alot of even the most exspensive dont, been driven by me the DFX man of the UK, they dont come any better.
.
On a serious note the way the DFX if set up correctly creaps up in volume as your getting near the selected buried item is amazing even if with crap all around it.
Its hard to explain soon as it locks in just takes you there deep, who needs a pinpointer when using the DFX, its in a world of its own, any experinced users know what planet im on.

Regards

[Tinkerer]

Hi Tinker
The DFX Whites circuit would be perfect for the increase in sound , problem is i dont have it..... unless you want me to dismantal mine to have a peek?? and do a bit of reverse
You realize though thats my babe the bees, goes places alot of even the most exspensive dont, been driven by me the DFX man of the UK, they dont come any better.
.
On a serious note the way the DFX if set up correctly creaps up in volume as your getting near the selected buried item is amazing even if with crap all around it.
Its hard to explain soon as it locks in just takes you there deep, who needs a pinpointer when using the DFX, its in a world of its own, any experinced users know what planet im on.

Regards

Thanks for the feedback.

Is the DFX a PI detector?

Does the pitch of the audio change with a target?

Tinkerer

[satdaveuk]

Thanks for the feedback.

Is the DFX a PI detector?

Does the pitch of the audio change with a target?

Tinkerer

Firstly no it not a PI its IB, Secondly it can be set up to audio change with target if required through its processor.

Maybe ive jumped the gun on that one

Regards

[Tinkerer]

Firstly no it not a PI its IB, Secondly it can be set up to audio change with target if required through its processor.

Maybe ive jumped the gun on that one

Regards

Processor, is the key word. I am sure it can be done by software in the MCU. I just don't know how to do it myself.

The timing is MCU controlled. It really would make sense to use the MCU also for the audio generation.

2 separate frequencies and the volume increase by PWM, that is duty cycle. But how to do the change in frequency at the same time?

Can anyone help?

Tinkerer

[Tinkerer]

Hi Tinkerer,
This is all sounding very good, and being public, I'd be able to build units for other people such as Rob, whose been looking for such a device for years. I will dig up that thread of Aziz's and study it.

I didn't answer your question about rubbish yesterday. There is a strange situation where you can dig 9 bits of rubbish, mainly rusted iron, to 1 bit of gold, these are areas where the Old Boys have been working the gold, and then patches off to the side that the Old Boys have missed will be 9 pieces of gold to one piece of rubbish, usually more modern such as spent ammunition, i.e. non-ferrous. So the ability to notch out iron would be a boon especially when the target is in water, and so much harder to retrieve.

The iron rubbish can be very small so coil i measurements would be useless as a disc solution I believe, especially with ground variations having similar effects.
In fact much of the gold is small, I attach an image of such, the coin is about 23mm across. 2 of the pieces are 0.07 grams, or 1 grain (480 per ozt). All these were detected with the Minelab GPX-4500 between 2 and 12 inches with a 14 x 9 inch elliptical mono coil.

The ultimate would be a machine having software control of the pulse and sample timings so that either large or small gold could be targeted, in fact my dream has been for a machine that automatically cycles through a couple of sequences tailored for both large and small gold. I've tried this on a std PI before and it sadly generated a lot of noise, noise that I believe SETA was developed by Minelab to overcome. They now have the ability to have a full spectrum of timings cycling, but have perhaps held off releasing it.

How sensitive do you feel the TEM can be made, is it perhaps only effective with coin sized targets and above? Is an earlier sample required to detect small targets as in conventional designs?

I know you're using Paul's UniPI, and I've been playing with a PIC24H DSP which is similar, and he's provided some of the source, so I'm sure we can collaborate sufficiently to get some code working.

The fly in the ointment for me at present is the disorder of my house and equipment, and in a couple of months I'll need to move everything out of my house into a shipping container while some walls and ceilings are rebuild.

Kind regards
Kev.

Hi Kev,

We are getting closer to your dream.
I have now developed the circuit to run at 4 different pulse rates.

6400cycle /sec, for smallish coils, like 40cm diameter. About 6A peak coil current.

4500cycles/sec, for coils up to 70cm diameter. About 9.5A coil peak coil current.

3600cycles/sec, for coils up to 1.2m diameter. About 11.5A peak coil current.

3200 cycles/sec, for coils up to 1.5m diameter. About 13A peak coil current.

All coils approximately 300uH.

The pulse rates can be selected with switches.

You can still use your 12V batteries, but will need 2 in series. In compensation, the PSU is very simple, linear, LDO's and low loss.

However, the power consumption for the 13A peak coil current will be about 1.6A or 40W. For the small coils it will be about 17W.

All the best

Tinkerer

[Midas]

Processor, is the key word. I am sure it can be done by software in the MCU. I just don't know how to do it myself.

The timing is MCU controlled. It really would make sense to use the MCU also for the audio generation.

2 separate frequencies and the volume increase by PWM, that is duty cycle. But how to do the change in frequency at the same time?

Can anyone help?

Tinkerer

You should be able to operate the pwm frequency at something over 20khz so you can't hear it and most speakers don't respond faster enough to transmit it anyway. The effect of playing two frequencies at once though is interesting. You end up with a 'beat frequency' that is determined by the difference between the two frequencies. At small differences it can be discerned but with large differences it merges into a strange tone. I guess you have to experiment to work our with what combinations of frequencies best conveys the two streams of information. Speaking of which what exactly is it that your planning on using to set the two frequencies, different sample points?

This site is good:
http://www.animations.physics.unsw.edu.au/jw/beats.htm
It has some examples... unfortunately most of which are rather unpleasant to listen to.
Midas

[Tinkerer]

You should be able to operate the pwm frequency at something over 20khz so you can't hear it and most speakers don't respond faster enough to transmit it anyway. The effect of playing two frequencies at once though is interesting. You end up with a 'beat frequency' that is determined by the difference between the two frequencies. At small differences it can be discerned but with large differences it merges into a strange tone. I guess you have to experiment to work our with what combinations of frequencies best conveys the two streams of information. Speaking of which what exactly is it that your planning on using to set the two frequencies, different sample points?

This site is good:
http://www.animations.physics.unsw.edu.au/jw/beats.htm
It has some examples... unfortunately most of which are rather unpleasant to listen to.
Midas

Thanks Midas, for the feedback.

Yes, I tried the beat frequency, it is very interesting, but takes quite a bit of a learning curve for the operator to make sense out of the variations.

The 2 frequency ranges we want for the TINKERERS_TEM, are not simultaneous. We want the pitch to go high for gold and go low for iron. With the CD4046, this is very easy. It has a VCO with a center frequency. A positive going signal, like for gold, increases the pitch, a negative signal, like for iron, decreases the pitch.

But, we also want the audio to increase in volume, for a target.

And then we have still another problem. The variation in pitch, of the CD4046, is about one decade. That means half a decade up or down from the center frequency. This seems quite OK, but the signal needs to swing all the way positive or negative for that.
However, our target signals are usually minimal. We want to be able to hear very minute signals as variations in the pitch. Something like 10mV.

Using a Log amplifier as the input to the CD4046 can solve that. All this is analog style.

I am sure it can also be done in digital style, but how?

Ah, and we want a fast response. Very important. We want to hear the target response with not more than about 10ms lag, for small coils, or 50ms lag for large coils. Nearly real time.

A crappy audio can ruin a good detector design.

An excellent audio can enhance the sensitivity and discrimination capability tremendously.

Tinkerer

[Midas]

Thanks Midas, for the feedback.

Yes, I tried the beat frequency, it is very interesting, but takes quite a bit of a learning curve for the operator to make sense out of the variations.

The 2 frequency ranges we want for the TINKERERS_TEM, are not simultaneous. We want the pitch to go high for gold and go low for iron. With the CD4046, this is very easy. It has a VCO with a center frequency. A positive going signal, like for gold, increases the pitch, a negative signal, like for iron, decreases the pitch.

But, we also want the audio to increase in volume, for a target.

And then we have still another problem. The variation in pitch, of the CD4046, is about one decade. That means half a decade up or down from the center frequency. This seems quite OK, but the signal needs to swing all the way positive or negative for that.
However, our target signals are usually minimal. We want to be able to hear very minute signals as variations in the pitch. Something like 10mV.

Using a Log amplifier as the input to the CD4046 can solve that. All this is analog style.

I am sure it can also be done in digital style, but how?

Ah, and we want a fast response. Very important. We want to hear the target response with not more than about 10ms lag, for small coils, or 50ms lag for large coils. Nearly real time.

A crappy audio can ruin a good detector design.

An excellent audio can enhance the sensitivity and discrimination capability tremendously.

Tinkerer

OK I get it now. I'm also sure what you want can be easily done using a micro controller. Resolving 10mv over 5v only requires a 10bit ADC which is on board most micros these days. Then you just need a little bit of maths, logic, and skills in a suitable programming language and your away. Of course once you have all this flexibility at your disposal you could do a whole lot more with the audio than generate a simple varying frequency. I think it would be cool if you could paint an 'audio picture' of the shape of the response. ie short pulse that rise and fall in frequency in a representation of the actual signal response. Then people could possibly learn to recognize the sound of particular objects. However to do all that you would probably need to digitize all of the samples before they are summed together.

Midas

[pelanj]

This project is of a high interest for me and if my knowledge permits, I will try to contribute my part. My field of focus is searching for (small) silver coins in ploughed and rolled fields and pastures. The coin diameters are starting at 10 mm. There is a lot of iron in the fields, so iron discrimination and either fast recovery or non-motion principle for unmasking the non-ferrous target is necessary. My secondary interest is hunting for coins and jewellery in the sand at the Baltic sea beaches. So far I have used VLF and FBS detectors and a military PI by Ebinger on the beaches. I dig targets (2.5 cm coin) from about 12-13" maximum with the detectors I have. I would really like to go deeper in the sand. In the dirt, I would like to get precise iron discrimination for coin sized objects to at least 12", to go deeper than conventional VLF detectors. If there was an option to use large coil for locating large deep objects, it would be great as well.

What I could help with? Unfortunately not much, but I have done some single chip and PLC programming and have a possibility to use MATLAB/Simulink for code generation (unfortunately not Embedded, but standard C/C++).