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LDC2112: LDC2114 More than four (4) keys?

Mike Tripoli
Genius 3295 points
Part Number: LDC2112
Other Parts Discussed in Thread: LDC2114

Hi,

I've looked at the inductive sensing devices a number of times for various applications. I have a question regarding the  LDC2114 (applies to the other devices as well perhaps). 

 The  LDC2114 device can sense four (4) "buttons". Is it *possible* that one could make a "series" arrangement of the sense coils, such that the device could report back which of the "buttons" is being depressed based upon the change in inductance from that particular key? Obviously the device is very capable of sensing very small changes in inductance. If, just thinking out loud, the keys (coils) in series are different sizes, the resulting measurement *should* indicate 'which key was pressed".  

Thanks,

Mike Tripoli

TI MVP

  • 0
    TI__Genius 14270 points
    Hello Mike,

    First - the reason that the LDC2114 cannot be muxed to multiple channels is due to the fact that the internal algorithms which process the sensor signals don't have the additional processing paths for a multiplexed sensor signal.

    You can construct a sensor which spans multiple physical buttons and weight each button differently for the functionality you propose. However, the resulting sensor may not be able to differentiate a light touch on a "big" button from a strong press on a "small" button.

    Regards,

    ChrisO
  • 0 in reply to Chris Oberhauser66
    Genius 3295 points

    Hi Chris,

    Thanks very much for your prompt reply. Excellent reply!

    So... If one were making a "washdown" control panel, cut into aluminum, theoretically it would be possible to "weight" the response by how deep the pocket cut into the back of panel (see drawings) one could vary the size of the coil (not shown) and the depth of the cut (shown). This would give different flexion to each of the "buttons". 

    It might take some experimenting to "get there", but *possible*... 

    Mike Tripoli

    SCARY Design

  • 0 in reply to Mike Tripoli
    TI__Genius 14270 points
    Hi Mike,

    I'm glad I was able to help. I do think this is a tricky effort. I would propose a few modifications to improve the viability of such an approach - first, perhaps you could put a rigid, precision thickness, non-conductive spacer to restrict the deflection to a fixed amount.

    Or second, you could try to use a pair of sensors, with opposite weighting factors for each sensor to better identify which button is pressed (the button shape could be elliptical to fit the pair of sensors).

    Or you could try to use something like a snap-dome design where the surface is popped out, for a larger deflection. Unlike traditional snap-domes, you could punch the entire array of buttons from one sheet of metal.

    Regards,

    ChrisO
  • 0 in reply to Chris Oberhauser66
    Genius 3295 points
    Thanks again, Chris.

    I agree, tricky effort. But I didn't get where I am today by playing by the rules ;)

    I'll admit, this is more of an academic inquiry than a practical one; I just like to push these little pieces of processed sand around to see how far they'll go...

    On a more "practical" (?!) note, ever since the fist inductive sensor was introduced (I think I may have been one of the first to buy the EVM for the single channel device), I've been intrigued by the idea of using one of these for a metal detector (like walk the beach). My experiments didn't get very far, I couldn't tune the thing, and I don't have access to a network analyzer...

    Thanks again,

    Mike