TINKERERS TIMING SCHEDULE

[nick_f]

A HAPPY NEW YEAR to you too.

If you want to build the detector please ask for the latest update of all circuits. I already have too many versions on this forum, so I am trying to post only one more, the final one.

Tinkerer

Hi Tinkerer,

I intend to build a detector in a modular form. Each major block separate on its own board, and all the modules connected via a main board.
This would allow, in my oppinion easy replacement of the blocks that need some improvements, while avoiding to build a whole new detector for each change in the diagram.
My version would integrate various features, many from your design, as well as whatever I will find interesting in other ones. I want to aproach a simple-to-complex approach, to get a simpler version functional, then to add improvements to each module.
At the moment I have many of the required components (still need 2 x LF398, I only bought 2 last time).
For the microcontroller at the moment I made code for a PIC16F628 and I can set the widths and delays on four outputs and display everything on an LCD. The steps have a resolution of 1us and adjustment is very easy.
Because of the LCD and keyboard I used a lot of the pins from my PIC, for the later versions I should use something with more pins. I am not sure how much would cost me to switch to dsPIC (I have two programmers for PIC16F family and many such microcontrollers). Besides, due to all kind of silly mistakes and accidents, I think I've blown like 20 microcontrollers already in the last two years and chances are poor that I will only need only one dsPIC...
On the other hand, it would be much better to work with 16 bit (my delays are at the moment only max 255us and I will have to some more work to extend the limit, I am working all in assembler.

Unfortunately my workshop from the spare bedroom has been packed to the garrage and I don't know where to work anymore... I am thinking to setup a minimal area somewhere, but even just the oscilloscope, power supply and soldering iron already require quite a lot of space...


Thanks for all your help.
Nicolae

[Tinkerer]

Hi Tinkerer,

I intend to build a detector in a modular form. Each major block separate on its own board, and all the modules connected via a main board.
This would allow, in my oppinion easy replacement of the blocks that need some improvements, while avoiding to build a whole new detector for each change in the diagram.
My version would integrate various features, many from your design, as well as whatever I will find interesting in other ones. I want to aproach a simple-to-complex approach, to get a simpler version functional, then to add improvements to each module.
At the moment I have many of the required components (still need 2 x LF398, I only bought 2 last time).
For the microcontroller at the moment I made code for a PIC16F628 and I can set the widths and delays on four outputs and display everything on an LCD. The steps have a resolution of 1us and adjustment is very easy.
Because of the LCD and keyboard I used a lot of the pins from my PIC, for the later versions I should use something with more pins. I am not sure how much would cost me to switch to dsPIC (I have two programmers for PIC16F family and many such microcontrollers). Besides, due to all kind of silly mistakes and accidents, I think I've blown like 20 microcontrollers already in the last two years and chances are poor that I will only need only one dsPIC...
On the other hand, it would be much better to work with 16 bit (my delays are at the moment only max 255us and I will have to some more work to extend the limit, I am working all in assembler.

Unfortunately my workshop from the spare bedroom has been packed to the garrage and I don't know where to work anymore... I am thinking to setup a minimal area somewhere, but even just the oscilloscope, power supply and soldering iron already require quite a lot of space...


Thanks for all your help.
Nicolae

Hi Nicolae,

It is a good idea to build the experimenter cct in discrete blocks, easier to make changes.
You can use integrators in place of the LF398, except for the Ground signal.

Are you using fully differential or only differential RX input? Mono coil or IB coil?

All the best

Tinkerer

[nick_f]

Hi Nicolae,

It is a good idea to build the experimenter cct in discrete blocks, easier to make changes.
You can use integrators in place of the LF398, except for the Ground signal.

Are you using fully differential or only differential RX input? Mono coil or IB coil?

All the best

Tinkerer

Hi Tinkerer,

I want to use the IB Coil, because of the clear advantages of this configuration. At the moment I don't even know the difference between fully differential or only differential Rx input. I think I will go with your preamplifier first (not sure if it is full or "only").
Since in modular form it will only require building of a pretty small board, there is a good chance I will play with many different configurations.

Regards,
Nicolae

[Mechanic]

Hi Tinkerer,

I am wondering if you have implemented any way of removing earths magnetic field when the coil is moved through the air or rotated?

Cheers Mick

[Tinkerer]

CANCELLING THE EARTH'S MAGNETIC FIELD

Hi Tinkerer,

I am wondering if you have implemented any way of removing earths magnetic field when the coil is moved through the air or rotated?

Cheers Mick

Hi Mick,

well, I wish you a very happy new year, may all your wishes come true.

The earth's magnetic field:

Iron stone concentrates the earth's magnetic field, therefore, in your part of the world, this is a factor to consider.
Let's look at a sweep speed of 1 meter per second and a mono coil of 30 cm diameter.
The coil sweep speed in the magnetic field generates a signal in the shape of a sine wave of 1Hz.
A target can only generate a response of minimum 3.3Hz, therefore a high pass filter can eliminate the earth's response.

Rotate the coil? DON'T!!! If you have to, rotate at the rotating speed of 1Hz.

Tinkerer

[Tinkerer]

IB-PI coil

Hi Tinkerer,

I want to use the IB Coil, because of the clear advantages of this configuration. At the moment I don't even know the difference between fully differential or only differential Rx input. I think I will go with your preamplifier first (not sure if it is full or "only").
Since in modular form it will only require building of a pretty small board, there is a good chance I will play with many different configurations.

Regards,
Nicolae

DD coils are more popular, but coaxial, concentric IB coils are better for experimenting. Look for Dave Emery's description for building such a coil. The Mosfet controlled Bucking works fine with it.

Tinkerer

[Mechanic]

Hi Mick,

well, I wish you a very happy new year, may all your wishes come true.

The earth's magnetic field:

Iron stone concentrates the earth's magnetic field, therefore, in your part of the world, this is a factor to consider.
Let's look at a sweep speed of 1 meter per second and a mono coil of 30 cm diameter.
The coil sweep speed in the magnetic field generates a signal in the shape of a sine wave of 1Hz.
A target can only generate a response of minimum 3.3Hz, therefore a high pass filter can eliminate the earth's response.

Rotate the coil? DON'T!!! If you have to, rotate at the rotating speed of 1Hz.

Tinkerer

Hi Tinkerer,

I wish you all the best for the new year too. Lets hope it is a nuggety one!

Now, as far as rotating the coil goes, if you are detecting on flat ground this is sort of ok, but if you are detecting mullok heaps then you are constantly rotating the coil.

Highly magnetic soils and hotrocks will also cause you(me) problems.
Also emi will be much more noticeable.

Have a look at the way the sd2000 cancels the earth field. At the end of the front end there is an amplifier which has no gain and its sole purpose is to invert the signal which is used for the second samples. It then has the 4066 for taking the samples followed by a 10 turn trimpot. The trimpot is used to fine tune the sample voltages so sample 1 and sample 2 cancel each other. By doing this it eliminates the earth magnetic field totally, eliminates response from magnetic soils and hotrocks and greatly reduces interference from emi.
On my detector, when I set up new timings, I turn the transmitter off and use a really strong magnet and wave it across the coil. If I get a response from this I then trim one of my samples until I get no response at all. On mine I can adjust sample widths in 125ns increments.

Now this may not work with your method of discrimination, but I thought it was worth mentioning anyway.

Cheers Mick

[Tinkerer]

Hi Tinkerer,

I wish you all the best for the new year too. Lets hope it is a nuggety one!

Now, as far as rotating the coil goes, if you are detecting on flat ground this is sort of ok, but if you are detecting mullok heaps then you are constantly rotating the coil.

Highly magnetic soils and hotrocks will also cause you(me) problems.
Also emi will be much more noticeable.

Have a look at the way the sd2000 cancels the earth field. At the end of the front end there is an amplifier which has no gain and its sole purpose is to invert the signal which is used for the second samples. It then has the 4066 for taking the samples followed by a 10 turn trimpot. The trimpot is used to fine tune the sample voltages so sample 1 and sample 2 cancel each other. By doing this it eliminates the earth magnetic field totally, eliminates response from magnetic soils and hotrocks and greatly reduces interference from emi.
On my detector, when I set up new timings, I turn the transmitter off and use a really strong magnet and wave it across the coil. If I get a response from this I then trim one of my samples until I get no response at all. On mine I can adjust sample widths in 125ns increments.

Now this may not work with your method of discrimination, but I thought it was worth mentioning anyway.

Cheers Mick

Hi Mick,

thanks for the feedback, very interesting information. I know nothing about the works of ML detectors.
When you zero the 2 samples with the trimpot, how to you do you know when it is zero. Do you have a readout or is it no sound or any other way?

I don't understand how the waving of a strong magnet across the coil can not produce a current in the coil.
When you trim the width of the samples, you change the integration of the signal, this has a filtering effect.
How fast do you wave the magnet? About the same as the sweep speed?

I take at least 3 different samples during each cycle. Then I null the 3 samples. The initial nulling is done manually with a trimpot. After that, the circuit updates the nulling automatically at each cycle. The updated Ground Cancel Signal is phase shifted and used as the reference voltage.
When a target is located, the detector automatically changes to pinpoint mode, where the Ground Cancel Signal is held stable, without updating, during some time.

Please tell me more about the functioning of your detector. When you ground balance or zero tune, do you move the coil up and down?

I assume your detector is a motion detector. How fast is your sweep speed?
When you detect in gullies and around rocks, is your sweep speed the same as when you are on flat ground?

Does the detector have any adjustments for different sweep speed?

Are there different settings for the Ground Balance, for more or less aggressive ground?

All the best

Tinkerer

[nick_f]

Hi Tinkerer,

On my detector, when I set up new timings, I turn the transmitter off and use a really strong magnet and wave it across the coil. If I get a response from this I then trim one of my samples until I get no response at all. On mine I can adjust sample widths in 125ns increments.
Cheers Mick

Hi Mick,

Which detector is that, Minelab or your own design? Do you adjust to 125ns in the code or from panel controls (user adjustable)?
Is it really necessary to have such a resolution? On my PIC, the user can adjust with a resolution of 1us.

Regards,
Nicolae

[Mechanic]

Hi Mick,

thanks for the feedback, very interesting information. I know nothing about the works of ML detectors.
When you zero the 2 samples with the trimpot, how to you do you know when it is zero. Do you have a readout or is it no sound or any other way?

Hi Tinkerer,

I hope you have the sd2000 schematic and pulse train timing schedule.
I no that it is zero because there is no audio response at all, with the transmitter turned off. When the adjustment is out just a little bit(1 turn) there is an audio response.

I don't understand how the waving of a strong magnet across the coil can not produce a current in the coil.
How fast do you wave the magnet? About the same as the sweep speed?

There is a huge voltage offset in the coil and at the end of the front end. Because sample 1 is added to -sample 2 this offset is canceled. If the magnet is right on the coil, as you pass over the windings the audio may still sound off, but that is because of the rapid change in field strength in that small area. In general waving the magnet over the coil as fast as you can won't give any response.

When you trim the width of the samples, you change the integration of the signal, this has a filtering effect.

When only adjusting a little bit(50-150ns) this gives the same effect as adjusting the trimpot. The trimpot allows you to fine tune even more precise than a 50ns step.

I take at least 3 different samples during each cycle. Then I null the 3 samples. The initial nulling is done manually with a trimpot. After that, the circuit updates the nulling automatically at each cycle. The updated Ground Cancel Signal is phase shifted and used as the reference voltage.
When a target is located, the detector automatically changes to pinpoint mode, where the Ground Cancel Signal is held stable, without updating, during some time.

Please tell me more about the functioning of your detector. When you ground balance or zero tune, do you move the coil up and down?

Yes the coil is raised and lowered to the ground while adjusting the GB pot.
Now there are 3 separate channels 1 GB channel and 2 target channels, one a short tc channel the other a long tc channel.

If the target channels are turned off and only the Gb channel left running, when the coil is lowered to the ground you will hear a rising pitch. If the ground channel is turned off and the target channels left on when the coil is lowered to the ground you will hear a falling pitch. The target samples are taken much earlier than the ground samples to try and minimize the amount of target signal that is left in the ground sample.
After the integrators the ground signal is added to the target channels and the amount of ground signal that is added in is trimmed via the GB pots. This added signal is then fed into a low pass filter, then a bandpass filter(sweep speed?) then an amplitude switch so only the strongest channel is heard.

I assume your detector is a motion detector. How fast is your sweep speed?

Yes it is. About 1- 1.5m/s

When you detect in gullies and around rocks, is your sweep speed the same as when you are on flat ground?

Not always, but you can easily hear a slight fluctuation in the threshold and sweep back to the area to see if it is consistent.

Does the detector have any adjustments for different sweep speed?

No, not really. I would have to change some capacitors. I'm not sure how well things would go if I had a switch to switch in different values.

Are there different settings for the Ground Balance, for more or less aggressive ground?

Not on the stock machines. A different value resistor can be switched across the 62k resistor(signal processing page,sd2000 schematic) to lower its resistance. Alternatively moving the first Gb sample a little earlier will have the same effect, but may include a little bit more target signal.

All the best

Tinkerer

You too!
Cheers Mick

[Mechanic]

Hi Mick,

Which detector is that, Minelab or your own design? Do you adjust to 125ns in the code or from panel controls (user adjustable)?
Is it really necessary to have such a resolution? On my PIC, the user can adjust with a resolution of 1us.

Regards,
Nicolae

Hi Nicolae,

It is(was) an sd2000. It has an atmega644 In charge of all of the pulse timings along with a nice quiet power supply for the analog, and a separate supply for the mcu. The timing adjustments are made in code. If you are only running one timing 1us resolution will be ok, provided you have some analog means of fine tuning signals. More timings may be possible without further analog adjustment but I'm not 100% certain.

Cheers Mick

[ZED]

Hey man im impressed ! Mick your really getting the hang of it.

Cheers Zed

oh yeh, happy new years everyone and a healthy one at that.

[Mechanic]

Hi Zed,

If you had never put together that schematic and published it for all to see, I would still be at square 1, looking at those numberless ic's scratching and shaking my head!

Thanks mate.

Cheers Mick

[ZED]

Found a niffty way to sync the p/supply to the mcu,will have to incorperate that in the next revision,will also see about using that ldo neg reg as well,any suggestions just pm me.

Zed

[ZED]

Hi Mick,

well, I wish you a very happy new year, may all your wishes come true.

The earth's magnetic field:

Iron stone concentrates the earth's magnetic field, therefore, in your part of the world, this is a factor to consider.
Let's look at a sweep speed of 1 meter per second and a mono coil of 30 cm diameter.
The coil sweep speed in the magnetic field generates a signal in the shape of a sine wave of 1Hz.
A target can only generate a response of minimum 3.3Hz, therefore a high pass filter can eliminate the earth's response.

Rotate the coil? DON'T!!! If you have to, rotate at the rotating speed of 1Hz.

Tinkerer

G`day Tinkerer,happy new years mate.

Tinkerer i wouldnt necessarily concur with a 3.3hz freq of a target signal,Sweep speed does vary alot,its not at all uncommon for pro operaters to sweep at speeds of 1 meter per 4 seconds,also large targets can give a very broad signal down to as low as 0.5hz per meter .

Zed