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juani_c

TI releasing something "game changing" on Sept 16th

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I like this inductance sensor a lot.  A really sensitive metal detector springs to mind (mpy powered of course)

But I see the dev board is $30, if it were sub $10 then it would be a game changer!

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Yes a boosterpack would be great.

 

Upon closer inspection the MSP430F5528 on the dev board is not easily programmable, none of the jtag/sbw pins are hooked up. 

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I would be interest to know the power consumption of this device. As it can define what role the device can play. I.e. Will it be possible to put it in use as a bug type battery operated wireless sensor?

 

A casual read on documentations shows the "analog" part is 5V though.

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@hilpka,  Nice write up.  I'm still waiting for mine. I assume you used the inductor on the EVM which

is rather small for metal detector use.  The detector distance is going to be related

to the size of the coil. Large diameter and High-Q is probably what is needed.

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Yes, I used the supplied PCB coil only. But I also looked at the WEBENCH tool for the LDC1000. When you try to calculate coils to detect 1cm copper object, you get at most a distance of about 6cm (though the tool only goes up to 7cm distance).

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I had first go on the EVM (it arrived on tuesday): http://blog.hendriklipka.de/archives/2013/09/ldc1000_test.html

This sensor is really sensitive (and accurate), but it is intended for small distances. So anybody thinking about using it as a metal detector will be disappointed.

Nice writeup. If you have any more interesting projects with it, let us know.

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I got some feedback from TI about my article. One of their product experts told me that, for a more general metal detector, one either needs a larger coil or should add a ferrite backing to it. So I did some more experiments, though not with a larger coil (so the results are not as good as they should be). I need to go into the coil winding business...

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Got my EVM and spent yesterday winding a coil and playing around with it.

 

On the whole this is a great little peripheral and very suitable for close proximity detection. 

but as a metal detector it suffers too much from pickup and interference 

 

First I split the EVM into controller, LDC1000 and coil adding 0.1" header connectors.

The controller to LDC1000 needed a 5x2 header which made it unfriendly for

direct plugging into a breadboard. 

 

 

I then wound a 15cm coil suitable for a metal detector, 50 turns of 26awg magnet wire

wound on the bottom of a plastic bottle. I measured L = 930uH and resonated at 28kHz

with a 3.7nF cap. The unloaded Q was 43. (wire from a degaussing circuit from

an old style CRT tv/monitor could be used instead)

 

 

Unfortunately the coil picks up a lot of interference which you can see as ripple when looking at the

envelope of the voltage across the coil. This results in considerable variation in

the frequency count  data and in the Rp proximity data. I adjusted the Fmin, Rpmin, Rpmax

register settings and the filter cap value so I was sure that the circuit was operating

correctly as per the datasheet.

 

Even ignoring the interference I suspect the resonating frequency is too low compared with

the LDC1000 oscillator gain control loop timing which is reducing the effective resolution of

the proximity data. 

 

In a regular metal detector interference is filtered out by various means, unfortunately the

LDC1000 is a complete control system with limited ablity to modify things. 

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