complete project

[Tinkerer]

No sorry, I'm being too vague again. I meant the high pass filters on the the gate signal lines from the PIC to the 4066. More specifically C12,R60 and C32,R61.

OK, I see now. I could not remember any high pass filters on this design.

C32,C12, R61, R60, are level shifters.

The PIC and TX are running on the 0V-12V battery rail to keep the switching noise isolated as much as possible.
I also suggest to make 2 separate PCB's and a shield between to keep the EMI pf the TX & PIC out of the analog circuit.

The analog part is running on +/-5V centered on the 6V rail.

This makes the PIC pulse to be -6V as seen by the analog GND, so the C32 and C12 bring the pulse up and centered on the Analog GND.

I have updated the design and added a resistor of 56k to the -5V, so that the PIC pulse triggers the CD4066 properly.

Thanks for bringing this to my attention. I will post a revised version of the design in a few days, when all the mistakes have been discovered and corrected.

SO, PLEASE, EVERYBODY SEARCH MISTAKES AND MAKE SUGGESTIONS, SO THAT WE CAN POST ALL THE CORRECTIONS IN ONE SINGLE POSTING.


Tinkerer

[mickstv]

http://www.geotech1.com/pages/metdet...planar_300.pdf

The above description by Dave Emery, is about the best I can come up with. One difference is the wire thickness, due to the high peak coil current.
Since the TINKERERS_SB TX has a resonant component, it is very important to keep the coil and cable resistance as low as possible.

I have posted many posts on the coil building, but they might be spread out over the whole forum. It takes some time to search for them.

Also look for my graphite shielding posts.

Eventually I intend to make a CD with all the pertinent information, posted over the years, but that will take some time too.

Tinkerer

Thanks Tinkerer. I've only ever mucked around with mono coils so this bucking coil business was new to me, but I understand now.


Mick

[Tinkerer]

I was thinking about just building the TX section first just to see how it actually works. The part I'm unsure about is the bucking coil arrangement, I'm sure you've posted about this coil design before but could you please explain how to build a basic coil again, or maybe you have a picture of one that you could post ?



Cheers
Mick

http://www.geotech1.com/pages/metdet/projects/coplanar/coplanar_300.pdf

The above description by Dave Emery, is about the best I can come up with. One difference is the wire thickness, due to the high peak coil current.
Since the TINKERERS_SB TX has a resonant component, it is very important to keep the coil and cable resistance as low as possible.

I have posted many posts on the coil building, but they might be spread out over the whole forum. It takes some time to search for them.

Also look for my graphite shielding posts.

Eventually I intend to make a CD with all the pertinent information, posted over the years, but that will take some time too.

Tinkerer

[Midas]

Thanks for the feedback, Midas.

Adding filters before the pre-amp, seems a good idea, we do really not want to amplify the noise coming form the coil.

The input is coming from a differential RX coil. Adding a low pass filter for common mode noise and a low pass filter for differential mode noise, reduces the bandwidth to the minimum necessary.
The minimum will depend on the intended targets. If we want to look for very small hypodermic needles, we need to keep the fo above 500kHz.
In other words, we eliminate all the noise above the desired target response frequency, or maybe we should call it Tau, since it is a single decay curve.

By the way, do not use these filters on a traditional PI. It will not work.

Tinkerer

No sorry, I'm being too vague again. I meant the high pass filters on the the gate signal lines from the PIC to the 4066. More specifically C12,R60 and C32,R61.

[mickstv]

The peak coil current is about 4A and the TX power consumption is about 100mA or 1.2W out of 12 battery, so the coil wire needs to be thick.

About AWG14 or AWG12 and about 300uH, not much different from the well known ML coils.

The main difference is that the coils are induction balanced.

OK, I will calculate some different coil specifications and post them in the days to come, say 40cm, 30cm and 20cm.

For a general purpose coil, I suggest about 40cm diameter.

Smaller coils will give more sensitivity and less detecting depth.

Tinkerer

I was thinking about just building the TX section first just to see how it actually works. The part I'm unsure about is the bucking coil arrangement, I'm sure you've posted about this coil design before but could you please explain how to build a basic coil again, or maybe you have a picture of one that you could post ?



Cheers
Mick

[Tinkerer]

Hi Tinkerer, no worries. Just wondering if you could post up some specific details for the coil ie:- diameter + turns ratio etc. Will it be suited to smaller coils 8 to 12"



Cheers
Mick

The peak coil current is about 4A and the TX power consumption is about 100mA or 1.2W out of 12 battery, so the coil wire needs to be thick.

About AWG14 or AWG12 and about 300uH, not much different from the well known ML coils.

The main difference is that the coils are induction balanced.

OK, I will calculate some different coil specifications and post them in the days to come, say 40cm, 30cm and 20cm.

For a general purpose coil, I suggest about 40cm diameter.

Smaller coils will give more sensitivity and less detecting depth.

Tinkerer

[Tinkerer]

Pinpointer or underwater detector?

Now that we have a new design on the table, we can decide what we could do with it.

For example, we could make a very powerful pinpointer.

Or we could make a very deep searching relic detector.

Or we could make a very deep searching underwater detector.

All these specific purpose detectors have one thing in common. They work well in non motion mode.

For each one of these purposes, specific changes in the design will need to be made, but the basics can remain the same.


And of course, I will post very soon, a motion detector model too.

The next step will be a detector that can be switched between motion and non motion.

With this new technology, the possible variations seem endless.

IT IS A WHOLE NEW HORIZON IN METAL DETECTORS!!!!!!!!!!!!

Tinkerer

[mickstv]

Thanks for the feedback, Mick.

This is the most basic I can go with a design, so obviously there are many things that can be improved.
For example, you can use a low noise LDO and you can add a regulator to the TX supply.

Better parts will give better results, like the CD4066, is just the cheapest analog switch, but there are many much better ones available, and so on.

Tinkerer

Hi Tinkerer, no worries. Just wondering if you could post up some specific details for the coil ie:- diameter + turns ratio etc. Will it be suited to smaller coils 8 to 12"



Cheers
Mick

[Tinkerer]

Hi Mick,
That's true but there are plenty of 5v LDO's with drop outs of less than 1v. Element 14 has 430 of them The -5v isn't as common but they still have 10 with dropouts of only 0.5v-0.6v.

Hi Tinkerer,
Thanks a lot for posting your new design. I've learnt heaps from your schematics.
I was wondering whats the purpose of the high pass filters on the sample lines?

Midas

Thanks for the feedback, Midas.

Adding filters before the pre-amp, seems a good idea, we do really not want to amplify the noise coming form the coil.

The input is coming from a differential RX coil. Adding a low pass filter for common mode noise and a low pass filter for differential mode noise, reduces the bandwidth to the minimum necessary.
The minimum will depend on the intended targets. If we want to look for very small hypodermic needles, we need to keep the fo above 500kHz.
In other words, we eliminate all the noise above the desired target response frequency, or maybe we should call it Tau, since it is a single decay curve.

By the way, do not use these filters on a traditional PI. It will not work.

Tinkerer

[Tinkerer]

Thanks Midas. Obviously I didn't look hard enough the last time I ordered some. LOL



Mick

Thanks for the feedback, Mick.

This is the most basic I can go with a design, so obviously there are many things that can be improved.
For example, you can use a low noise LDO and you can add a regulator to the TX supply.

Better parts will give better results, like the CD4066, is just the cheapest analog switch, but there are many much better ones available, and so on.

Tinkerer

[mickstv]

Hi Mick,
That's true but there are plenty of 5v LDO's with drop outs of less than 1v. Element 14 has 430 of them The -5v isn't as common but they still have 10 with dropouts of only 0.5v-0.6v.

Hi Tinkerer,
Thanks a lot for posting your new design. I've learnt heaps from your schematics.
I was wondering whats the purpose of the high pass filters on the sample lines?

Midas

Thanks Midas. Obviously I didn't look hard enough the last time I ordered some. LOL



Mick

[Midas]

Hi Tinkerer, certainly looks good mate. One thing I picked up on which may cause problems are the LDO's if they are standard 78L05 and 79L05 they normally have a minimum input voltage requirement, normally about 2 volts above the rated output, any less and they won't regulate correctly.



Cheers
Mick

Hi Mick,
That's true but there are plenty of 5v LDO's with drop outs of less than 1v. Element 14 has 430 of them The -5v isn't as common but they still have 10 with dropouts of only 0.5v-0.6v.

Hi Tinkerer,
Thanks a lot for posting your new design. I've learnt heaps from your schematics.
I was wondering whats the purpose of the high pass filters on the sample lines?

Midas

[mickstv]

Hi Tinkerer, certainly looks good mate. One thing I picked up on which may cause problems are the LDO's if they are standard 78L05 and 79L05 they normally have a minimum input voltage requirement, normally about 2 volts above the rated output, any less and they won't regulate correctly.



Cheers
Mick

[Tinkerer]

Hi Tinkerer,
I was thinking about the audio options and if I wanted to have the audio I have described in one of my posts, it would need another PIC programmed to just convert the samples to audio. For the front end part, you need precise timing. The audio needs much less computations, but at the same time, it needs to be precise anyway. Is it acceptable that the detetor would have a PIC for timing and another PIC for audio processing?

Hi pelanj,

thanks for the feedback.

PIC's are cheap. There is no problem of using 2. For just the timing, I can also change to a smaller, cheaper PIC.

It might be a good idea for you to breadboard the RX board above. For the TX you will need to solder the Mosfet, because it runs with about 4.5A at several hundred Volt, but all the rest runs OK on a breadboard.
The RX circuit has an audio, but the audio response is not as good as I would like it to have.
The human ear is sensitive to slight changes in the pitch, but for good target recognition we need about 2 cents of change.
For a 500Hz center audio frequency, this means we want about 10 to 20Hz change in frequency for 10 to 20mV of minimum target response.

Now, it is easy to make a window comparator that switches the audio ON at 10 or 20mV, but that results in a lot of noise or falsing, when the audio switches ON and OFF, every time some noise peaks above that level.

The analog audio on the TINKERERS_SB_NM, has a floating center frequency. The ear can easily distinguish the downward change in pitch for iron targets and upward change for gold, while the center frequency follows the ground between manual ground balance.

If we could do something similar, digitally, we would have something good.
And of course, the analog circuit above, does not vary the volume with target, and that would make it so much better.

Tinkerer

[pelanj]

Hi Tinkerer,
I was thinking about the audio options and if I wanted to have the audio I have described in one of my posts, it would need another PIC programmed to just convert the samples to audio. For the front end part, you need precise timing. The audio needs much less computations, but at the same time, it needs to be precise anyway. Is it acceptable that the detetor would have a PIC for timing and another PIC for audio processing?