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loop_y0u
Level 4
Level 4
25 replies posted 50 sign-ins 10 questions asked

Hi Community,

 

I want to know how can I know the difference between a Real Touch on a CapSense Peripheral and Ghost Touch. I'm facing a lot of issue on my Touch Switches which automatically gets Turned on and Off. 

I didn't put any air gap between the Surface and Touch Pad. 

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1 Solution
Arpit_S
Moderator
Moderator
Moderator
100 solutions authored 250 sign-ins 10 likes given

Hi @loop_y0u ,

 

Valid Touch: The finger threshold parameter is used along with the hysteresis parameter to determine the sensor state as below:

Sensor state = ON if Signal ≥ Finger Tℎresℎold + Hysteresis
                              OFF if Signal ≤ Finger Tℎresℎold − Hysteresis

It is recommended to set finger threshold to 80 percent of the signal. This setting allows enough margin to
reliably detect sensor ON/OFF status over signal variations across multiple PCBs.

 

I would recommend you to go through the below mentioned Parameters: 

Baseline

Baseline Update Algorithm

Finger Threshold

Hysteresis

Noise Threshold

Negative Noise Threshold

Low Baseline Reset

Debounce

Sensor Auto reset

You can find these parameters in CAPSENSE Design guide https://www.infineon.com/dgdl/Infineon-AN85951_PSoC_4_and_PSoC_6_MCU_CapSense_Design_Guide-Applicati... Page Number 93 to 97.

 

If you have tuning related issue then I'd recommend you to refer to Section 5.3.2.4 Button widget tuning in CAPSENSE Design guide https://www.infineon.com/dgdl/Infineon-AN85951_PSoC_4_and_PSoC_6_MCU_CapSense_Design_Guide-Applicati... 

 

Ghost Touch:  In CAPSENSE Sigma Delta mode (CSD Mode), each button consists of a row sensor and a column sensor, as Figure 15(CAPSENSE Design Guide Page 23) shows. When a button is touched, both row and column sensors of that button become active. The CSD-based matrix button should be used only if the user is expected to touch one button at a time. If the user touches more than one diagonally opposite buttons, the finger location cannot be resolved as Figure 16(CAPSENSE Design Guide Page 24) shows. This effect is called as ghost effect, which is considered an invalid condition.

Mutual-capacitance or CSX CAPSENSE MODE is the recommended sensing method for matrix buttons because this method is not affected from the ghost touch phenomena and provides better SNR for high Cp sensors. This is because it senses mutual-capacitance formed at each intersection rather than sensing rows and columns as shown in Figure 17(CAPSENSE Design Guide Page 25) . Applications that require simultaneous sensing of multiple buttons, such as a keyboard with Shift, Ctrl, and Alt keys can use CSX sensing method or you should design the Shift, Ctrl, and Alt keys as individual CSD buttons.

 

Ghost touch is not False touch.

 

Hope this helps!
Thanks!
Kind Regards

Arpit Srivastav

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1 Reply
Arpit_S
Moderator
Moderator
Moderator
100 solutions authored 250 sign-ins 10 likes given

Hi @loop_y0u ,

 

Valid Touch: The finger threshold parameter is used along with the hysteresis parameter to determine the sensor state as below:

Sensor state = ON if Signal ≥ Finger Tℎresℎold + Hysteresis
                              OFF if Signal ≤ Finger Tℎresℎold − Hysteresis

It is recommended to set finger threshold to 80 percent of the signal. This setting allows enough margin to
reliably detect sensor ON/OFF status over signal variations across multiple PCBs.

 

I would recommend you to go through the below mentioned Parameters: 

Baseline

Baseline Update Algorithm

Finger Threshold

Hysteresis

Noise Threshold

Negative Noise Threshold

Low Baseline Reset

Debounce

Sensor Auto reset

You can find these parameters in CAPSENSE Design guide https://www.infineon.com/dgdl/Infineon-AN85951_PSoC_4_and_PSoC_6_MCU_CapSense_Design_Guide-Applicati... Page Number 93 to 97.

 

If you have tuning related issue then I'd recommend you to refer to Section 5.3.2.4 Button widget tuning in CAPSENSE Design guide https://www.infineon.com/dgdl/Infineon-AN85951_PSoC_4_and_PSoC_6_MCU_CapSense_Design_Guide-Applicati... 

 

Ghost Touch:  In CAPSENSE Sigma Delta mode (CSD Mode), each button consists of a row sensor and a column sensor, as Figure 15(CAPSENSE Design Guide Page 23) shows. When a button is touched, both row and column sensors of that button become active. The CSD-based matrix button should be used only if the user is expected to touch one button at a time. If the user touches more than one diagonally opposite buttons, the finger location cannot be resolved as Figure 16(CAPSENSE Design Guide Page 24) shows. This effect is called as ghost effect, which is considered an invalid condition.

Mutual-capacitance or CSX CAPSENSE MODE is the recommended sensing method for matrix buttons because this method is not affected from the ghost touch phenomena and provides better SNR for high Cp sensors. This is because it senses mutual-capacitance formed at each intersection rather than sensing rows and columns as shown in Figure 17(CAPSENSE Design Guide Page 25) . Applications that require simultaneous sensing of multiple buttons, such as a keyboard with Shift, Ctrl, and Alt keys can use CSX sensing method or you should design the Shift, Ctrl, and Alt keys as individual CSD buttons.

 

Ghost touch is not False touch.

 

Hope this helps!
Thanks!
Kind Regards

Arpit Srivastav

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