TIDUE90 July   2018

 

  1.    Description
  2.    Resources
  3.    Features
  4.    Applications
  5.    Design Images
  6. 1System Description
    1. 1.1 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Classification of Scenarios With Liquid Present
      2. 2.2.2 Liquid Influence on Capacitive Touch Sensing
      3. 2.2.3 Self Capacitance and Mutual Capacitance
        1. 2.2.3.1 Self Capacitance
        2. 2.2.3.2 Mutual Capacitance
      4. 2.2.4 Other Considerations
    3. 2.3 Highlighted Products
      1. 2.3.1 MSP430FR2633
    4. 2.4 System Design Theory
      1. 2.4.1 Shield Sensor Electrodes
      2. 2.4.2 Mutual Capacitance Shielding
      3. 2.4.3 Design for Noise Immunity
      4. 2.4.4 Power Supply Grounding Effect
  8. 3Hardware, Software, Test Requirements, and Test Results
    1. 3.1 Required Hardware and Software
      1. 3.1.1 Hardware
      2. 3.1.2 Software
    2. 3.2 Test and Results
      1. 3.2.1 Liquid Test With Well Grounded Power Supply
        1. 3.2.1.1 Continuous Water Flow Test
        2. 3.2.1.2 Continuous Water Spray Test
      2. 3.2.2 Conductive Noise Immunity Test
      3. 3.2.3 Liquid Test With Battery-Powered Supply
        1. 3.2.3.1 Continuous Water Flow Test
        2. 3.2.3.2 Continuous Water Spray Test
      4. 3.2.4 Third Party Test Report
  9. 4Design Files
    1. 4.1 Schematics
    2. 4.2 Bill of Materials
    3. 4.3 PCB Layout Recommendations
      1. 4.3.1 Layout Prints
    4. 4.4 Altium Project
    5. 4.5 Gerber Files
    6. 4.6 Assembly Drawings
  10. 5Software Files
  11. 6Related Documentation
    1. 6.1 Trademarks
  12. 7About the Author

3.1.2 Software

The TIDM-1021 firmware uses the CapTIvate software library to process raw capacitive measurements from the CapTIvate peripheral on the MSP430FR2633 MCU. This software is based on code generated by the CapTIvate Design Center, and the application layer call back function is added to provide the liquid tolerance feature and to control the feedback (the LED and buzzer).

The process of creating this firmware:

  1. Use CapTIvate Design Center to generate the code based on the sensor configuration.
  2. Disable the negative touch automatic recalibration feature.
    Remove the MAP_CAPT_testForNegativeTouchRecalibration() function in the CAPT_updateUI() function in the CAPT_Manager.c file.
  3. Enable the noise immunity feature.
    Change CAPT_CONDUCTED_NOISE_IMMUNITY_ENABLE to true in the CAPT_UserConfig.h file.
  4. Implement the call back function. Figure 15 shows the callback function flow chart.

The callback function will first check if there is a "negative touch" to determine whether to halt the LTA. This is to prevent the LTA to track with the "negative touch" count which could trigger false touch detection after the liquid is removed. And then the callback will determine whether to update touched button based on the previous touch status. The callback uses the dominate button algorithm to determine the actual touched button after the sensor touch is detected.

For more information about the firmware and the CapTIvate Design Center project, download them from the TIDM-1021 page, and visit CapTIvate Design Center GUI page CapTIvate Design Center GUI.

TIDM-1021 tida-1021-callback-function-flow-chart-block-diagram.gifFigure 15. Callback Function Flow Chart