SNOA951 June   2016

 

  1.   Inductive Sensing Touch-On-Metal Buttons Design Guide
    1.     Trademarks
    2. 1 ToM Basics
    3. 2 How Are Inductive Touch-On-Metal Buttons Implemented?
    4. 3 System Design Procedure
      1. 3.1 Mechanical System Design
        1. 3.1.1 Designing for Natural Button Force
          1. 3.1.1.1 Metal Composition
          2. 3.1.1.2 Metal Thickness
          3. 3.1.1.3 Mechanical Structure of the Button
        2. 3.1.2 Target Distance
        3. 3.1.3 Mechanical Isolation
        4. 3.1.4 Mounting Techniques
      2. 3.2 Sensor Design
        1. 3.2.1 PCB Design
        2. 3.2.2 Sensor Frequency Selection
        3. 3.2.3 Sensor Amplitude Selection
      3. 3.3 Other Considerations
        1. 3.3.1 Button Quantity and Multiplexing
        2. 3.3.2 Power Consumption
        3. 3.3.3 Software Algorithm
        4. 3.3.4 EMI Emissions Testing
      4. 3.4 Design Implementation
    5. 4 Results
    6. 5 Summary
    7. 6 Additional resources

5 Summary

LDC technology can be used to create robust, non-wearing, and versatile buttons for human-machine interface needs. With proper mechanical and sensor design, an inductance-to-digital converter can detect even very light button presses of 0.5 N.

The following guidelines are presented in this report:

  1. Mechanical system design considerations including the metal material, thickness, and shape of the buttons are discussed. The quantity and arrangement of buttons for mechanical isolation as well as the optimal target-to-sensor spacing which influences the response of the system. Metal etching and mounting techniques are also presented.
  2. Best sensor design practices ensure that the LDC can detect microscopic deflection in metal.
  3. Other considerations such as multiplexing multiple buttons, advanced button detection algorithms, power consumption, and EMI performance are explained.

This design is scalable in both resolution and sample rate making the LDC useful in a wide variety of applications from systems that need to detect small µm changes to systems that require update rates of several hundred times per second.