SNOA951 June   2016 LDC1312 , LDC1312-Q1 , LDC1314 , LDC1314-Q1 , LDC1612 , LDC1612-Q1 , LDC1614 , LDC1614-Q1

 

  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

3.1.3 Mechanical Isolation

When multiple buttons are present in a system, it is possible for undesirable mechanical interaction between different buttons to occur. For example, when pressing button A, the contiguous metal surface may deform in such a manner that a significant amount of movement occurs over the neighboring button B sensor, and could appear as an unintended button press of button B. The following principles can be applied to reduce the mechanical crosstalk between adjacent buttons during an active press:

  1. Physical supports between buttons or standoffs can facilitate stronger metal deformation on the button that is pressed, as shown in Figure 5.
  2. Ensuring a larger physical deflection for the intended button. From an electrical perspective, a large signal-to-noise ratio between a true button press versus an undesired detection is the easiest way to detect the correct button press event. Using thinner metal or selecting materials with a low Young’s modulus ensures that metals are easier to deform and have less impact on the neighboring buttons. For example, aluminum is more flexible than many stainless steel alloys.
  3. Increasing the distance or adding grooves between adjacent buttons improves mechanical isolation. For cross-talk minimization, button-to-button separation should also be greater than one coil diameter.