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CCS/MSP430FR2532: capacitive sensor calibration (designed by CDC)

Aref Smiley
Intellectual 300 points
Part Number: MSP430FR2532


Tool/software: Code Composer Studio

Hi, 

I used Captivate design center (CDC) to generate CCS codes for my sensor board which has MSP430FR2532. I defined a self-capacitance sensor for one of the CAP pins and the pin is connected to an electrode. I am monitoring the results in the serial port. 

The sensor works great and the serial port shows numbers ranged from  20 to ~ 500. 

Can you please tell me how I can calibrate the sensor? in other words, what should be the real capacitance values of the represented numbers in the serial port? what is the expected range of capacitance of my sensor? 

For calibration, can I choose five capacitors with different values, for example, and connect the electrode to one capacitor pin while the other pin is grounded? So I can find the representative values. 

Thanks,

Aref

  • 0
    TI__Expert 5490 points
    Hello Aref,

    Thanks for your posting.
    I have couple of questions would like to clarify with you:
    1. You said the serial port shows numbers ranged from 20 to ~500. What do you mean by serial port shows the number? Are you using the design center to monitor the sensor data? If so can you tell me which number is showing 20 to ~500?

    2. You can calibrate the sensor with the CapTIvate Design Center. When connect the device to Design center you can calibrate and tune the sensor through the GUI interface. For more information please see this link: software-dl.ti.com/.../ch_designcenter.html

    3. You can calibrate your sensors individually with different configurations. However, CapTIvate technology does not measure the absolute capacitance value but measure the relative capacitance changes for capacitive touch sensing. For more information about CapTIvate technology please see this link: software-dl.ti.com/.../ch_technology.html

    4. Could you please share with me what you try to achieve with the CapTIvate device?

    Please let me know if you have any questions.

    Thanks,
    Yiding
  • 0 in reply to Yiding Luo
    TI__Expert 5490 points
    Hello Aref,

    Do you still have any questions regarding calibrating the device?

    Thanks,
    Yiding
  • 0 in reply to Yiding Luo
    Intellectual 300 points

    Thank you so much for your response. Yes, I am still working on it. but not sure if I am in a right track. I am answering your questions here, so you may be able to help me more on this. I really appreciate it: 

    1. You said the serial port shows numbers ranged from 20 to ~500. What do you mean by serial port shows the number? Are you using the design center to monitor the sensor data? If so can you tell me which number is showing 20 to ~500?

    I disabled the UART communication of the CDC and use the UART  to monitor the rawSample (by serial port) which gives me the RawCount:

    extern tElement BTN00_E00;
    // uint16_t rawSample;
    CAPT_updateSensorRawCount(
    &BTN00, // Pointer to the sensor to update
    eStandard, // Conversion type
    e2xOversampling, // Oversampling type
    LPM0_bits // Low power mode to use
    );
    rawSample = BTN00_E00.pRawCount[0];

    2. You can calibrate the sensor with the CapTIvate Design Center. When connect the device to Design center you can calibrate and tune the sensor through the GUI interface. For more information please see this link: software-dl.ti.com/.../ch_designcenter.html

    I already ordered the required components and working on that.

    3. You can calibrate your sensors individually with different configurations. However, CapTIvate technology does not measure the absolute capacitance value but measure the relative capacitance changes for capacitive touch sensing. For more information about CapTIvate technology please see this link: software-dl.ti.com/.../ch_technology.html

    Correct. This may be useful for my application.

    4. Could you please share with me what you try to achieve with the CapTIvate device?

    I am trying to measure the capacitive changes of a certain liquid at different state (Solid, liquid, gas)

    Please let me know if you have any questions. 

    Thanks 

    Aref

  • 0 in reply to Aref Smiley
    TI__Expert 5490 points
    Hello Aref,

    To detect the capacitive changes of a certain liquid at different state, I think you may need to develop the algorithm to calibrate under different states and also take in consideration of how the temperature and humidity can affect your measurement result.
  • 0 in reply to Yiding Luo
    Intellectual 300 points

    Thanks for your help.

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