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LDC1614: Inductive push button sensing above OLED display with LDC1614

Jo
Intellectual 290 points
Part Number: LDC1614

Hello there,

I would like to share an idea how to realize an inductive push button sensing solution above a small OLED display.
In a prototype mockup, it worked well for me with an LDC1614 device, but since then I have not brought it to production status:

The sensing coil was wire-wound around a plexiglass disk, a PCB in form of ring shape might work as well but have not tested it.

The key-element of this construction is the spring between the two plexiglass bodies. Once compressed as far as possible, it will
act as a short-circuit winding, causing cause a huge inductance change in the sensing coil below.

I found this works well and reliable, even with a button-to-sensing coil distance of more than twice the coil diameter.

Hope this could be a useful application for some readers.

Regards,

Jo 


  • 0
    TI__Mastermind 18545 points

    Hello Jo, 

    Thank you for sharing your implementation. Would you be willing to also share information on your mechanical stackup such as the thickness of each layer and information on your spring (such as number of turns, thickness, and height)? 

    Best Regards, 

    Justin Beigel

  • 0 in reply to Justin Beigel
    Intellectual 290 points

    Hello Justin,

    I did not keep the mechanical stack alive, because the project goal changed in a way that rear mounted displays
    were not required anymore. I recall the following, for the short-circuit winding I have used a key-ring of about 20mm
    in diameter. To make it a compressible spring, it has to be stretched enough- otherwise it would also act as short-
    circuit winding all the time:

    The sensing coils was wire-wound 38 SWG, but I don't remember number of turns and tank frequency (something between 20-30 turns).
    The coil shape was rectangular about 20mm x 30mm, only in provided sketch I have "updated" this to a circular coil.

    One thing to consider, when building this:

    Ironically, it will turn a contactless inductive sensing solution into  non-contactless one, because the compressible spring acts as
    a mechanical switch at the point in time when it is a short-circuit winding. Thus, contact bouncing is something to be dealt with.

    Regards,

    Jo

  • 0 in reply to Jo
    Intellectual 290 points

    I think picture of spring was missing:

  • 0 in reply to Jo
    Intellectual 290 points

    Hello Justin,

    Maybe some other application come to mind, where the usage of a short-circuit winding acting as target is more useful:
    One could think of an optical application with lenses or filter elements to be pivoted into an optical path of a system.

    Then, with a minimal amount of metal (basically just a thin ring around that optical element) would be required for reliable
    position detection, i.e filter inside or outside the optical path.

    Regards,

    Jo

  • 0 in reply to Jo
    TI__Mastermind 18545 points

    Hello Jo, 

    Thank you for the additional information. This is definitely an interesting use case for the device. 

    Best Regards, 

    Justin Beigel