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

3.2.1.2 Continuous Water Spray Test

Test Setup

The test setup is similar to the continuous water flow test in Section 3.2.1.1. The difference is a spray nozzle added on the plastic water tube to provide a continuous water spray on the touch sensor area (see Figure 20).

TIDM-1021 tidm-1021-continuously-spray-water-testing-setup-photograph.pngFigure 20. Continuous Water Spray Test Setup

Test Procedures

The test procedures are the same as the continuous water flow testing (see Section 3.2.1.1).

Test Result

Figure 21 shows the sensor measurement count result. The result is similar to the continuous water flow test result (see Section 3.2.1.1). The difference is that when the continuous water spray is applied on the touch sensor area, the measurement count is not as consistent as the continuous water flow test case. This is because the spray water does not contact the touch sensor area consistently. The "negative touch" behavior is still present, which means that the spray water causes the measurement result to go in the opposite direction of a touch event. Therefore, there is no false touch detection. While the continuous water spray is applied on the touch sensor area, each touch event still causes a distinguishable count increase for the touched button. Based on this test result and by using the dominant button lock algorithm (see Section 3.1.2), the system can reliably operate when exposed to continuous water spray, with no false touch detections and with accurate detection of a button touch.

TIDM-1021 D004_TIDUE90.gifFigure 21. Sensor Count Result With Continuous Water Spray (Well Grounded Power Supply)