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Offline 6666
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« Reply #20 on: April 13, 2015, 10:01:29 pm »
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This is about as simple as a uC PI gets.

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« Reply #21 on: April 14, 2015, 12:31:42 am »
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if you have a separated search head with transmit and receive coil, you can go higher timings Wink (at least over 1khz)

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my machines at work http://mueller-meteoriten.de


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« Reply #22 on: April 14, 2015, 03:25:54 am »
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Does any one have a schematic of a pi with a separate receive coil that I can have a look at?
I have a fair idea how one would implement it but I would just like to confirm.

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« Reply #23 on: April 14, 2015, 05:03:49 am »
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Do you want the separate tx and rx coil schematic for a Nch fet or a Pch fet
here is one for a Nch fet.
Had to do a screen dump as PDF too big


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« Last Edit: April 14, 2015, 05:05:05 am by 6666 »
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« Reply #24 on: April 16, 2015, 08:56:55 pm »
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I googled stm32f4 just to see what they are, there appears to be a good selection of development boards available which after a few mods
would make a nice controller to plug into a single layer through hole PI pcb .



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« Reply #25 on: April 16, 2015, 10:38:43 pm »
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Yea that’s what I am thinking.
I am currently using the stm32f4 discovery..

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If you want to have a look.

My idea at the moment is to make a 4 layer sandwich with single or double layer bards like so..

----------------   <LCD Breakout board
----------------   <Stm32f4 Discovery
----------------   <Detector circuit
----------------   <Power supply

All connected together via pin headers.
I will modify some of the stm32f4 pins to come out via the top so the lcd board can connect.
This way I could save space
Thoughts.

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« Reply #26 on: April 18, 2015, 12:26:48 pm »
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Gtdavid, what's your angle using the micro and display?
Is it mostly controlling an existing detector, managing the signal generation and detection, displaying the result graphically or in numbers, analysing the signals from the detecting circuit or maybe even all of those?
Sounds really interesting if someone would put effort in doing a good analysis of the received signal from the Rx coil and giving a graphical presentation of it...

Anyway, I will follow your progress with interest.

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« Reply #27 on: April 19, 2015, 03:16:01 am »
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It will be a new detector based on ones I research and ideas/info people give me.
A lot of the circuits are going to taken over by the micro for example pulse gen, delay gen, sample processing and also audio using the dac on the stm32f4.
The new circuit will be mostly be coil switching, signal amplification and power supply’s.

On the power supply issue. I am reading a fair bit of conflicting info on the net.
What is better more amps or more volts?
I know power usage in watts would not change all that much but is there any advantage running the coil at say 12v opposed to 7v/9v ?
I am currently building the power supply as my current one is a bit unstable so I figure I should just build one for the detector and be done with it.
Thanks.

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« Last Edit: April 19, 2015, 03:17:18 am by gtdavid »
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« Reply #28 on: April 19, 2015, 04:26:30 am »
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Hi again,
I think that the supply voltage, coil and power supply circuitry can be dimensioned to begin with as you say.

First some basics in short:
The maximum current that can be drawn through the coil is mainly dependant on two things, the voltage that is applied to the coil and the winding's resistance.
The coil's resistance depends on the wire's resistivity, the total length of the wire in the coil and the wire thickness.
The magnetic field occuring is mainly dependant on the current through the coil and the number of turns, the physical size of the coil has also influence.
When applying voltage to a coil, the current will rise linearily with time until the maximum current (=voltage/resistance) is reached.
The time to reach the maximum current depends on the inductance of the coil, in turn depending on the number of turns and the coil's "form factor" (thickness/dia).

Thus, it is no point keeping the pulse length longer than this time, all excess power will be waisted and the impulse will also be weakened.

The influence on an object to be found is depending on a lot of stuff, but mainly the distance to the coil and the angle to the coil's center line, simply put.
This influence gives reason to a field emitted from the object when the exciting field disappears.
This emitted field can be picked up by the same coil, or better another coil placed a little offset from the transmitting coil.
The waweform and amplitude of this signal tells much about the material, size and other things on the object, and also the distance/angle to it.

Then, the power supply must be able to cope with this special case of load (short pulse, high current), but the mean (over time) power to the coil depends on the pulse length in relation to the pulse repetition rate.
All other supply currents must of course be added to this to find the power supplie's requirements.
The battery voltage must be selected depending on all previous parameters, or be set to a value and used as parameters in the earlier calculations (which I would do).
Also, as you may see, higher voltage gives possibility to a high coil current ,which not necessarily is a great advantage in overall performance.

It is ,as you might see, important to break down the design in small blocks that can be handled.


Hopefully this will help you and others, I can assist some in the calculations but my time is limited right now because of a rough load at work.

If I missed or mixed something up, I can only refer to my age combined with little time to spend. Wise



Best wishes!


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« Reply #29 on: April 19, 2015, 05:47:43 pm »
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The current draw of the 3-4 most popular PI projects is around 100mA @ 10-12v, depending on the tuning, maybe as much as 150mA or as low as 80mA, powered by a bunch of AA alkaline or NiMH cells, Lipo's are becoming more popular for high capacity with low weight.

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« Last Edit: April 19, 2015, 06:02:29 pm by 6666 »
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