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PSoC™ 4 Forum Discussions

Tim_Shih
Level 4
Level 4
50 replies posted 50 questions asked 100 sign-ins

Dear Receiver, 

Could you please check the attached picture ?! 

In the picture, we can see "GUARD" and "SHIELD" pins.

I feel confused about these 2 pins.

Does PSoC 4 have these 2 pins ("GUARD" and "SHIELD") !?

I think these 2 pins are all ground (GND). Am I right ?!

Thank you so much.   

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1 Solution
ncbs
Moderator
Moderator
Moderator
50 likes received 250 sign-ins 250 replies posted

Hi @Tim_Shih.,

SHIELD:

In the presence of water droplets, C_LD (capacitance due to the liquid droplet) increases the capacitance of the system. The added capacitance draws an additional charge from the AMUXBUS. This gets reflected as an increase in the raw count and can contribute to a false trigger. Shield electrode will help us avoid false triggers in the presence of liquid droplets.

ncbs_0-1646482038845.png

C_LD contributes to false triggers.

 

Shield electrode is used for liquid tolerant operation. The shield electrode is driven by the driven shield waveform, which is the buffered in-phase version of the sensor waveform. 

ncbs_1-1646482179441.png

Driven shield signal is a buffered and in-phase version of sensor waveform

The hatch fill around the sensor is driven with this "driven-shield signal". The voltage on both sides of the liquid droplet remains at the same potential. Because of driven shield, the capacitance C_LD added by the liquid droplet does not draw any additional charge from the AMUX bus and hence the effect of capacitance C_LD is nullified.

ncbs_2-1646482403516.png

Shield overcomes the effects of liquid droplets

 

GUARD SENSOR:

When streams of liquid are present, the added capacitance will be much larger than that contributed by just a few water droplets, and hence the effect of the shield will be lessened. A guard sensor is a copper trace that surrounds all the sensors on the PCB. A guard sensor is similar to a button sensor and is used to detect the presence of streaming liquids. 

ncbs_0-1646483702732.png

Guard sensor as a copper trace present around other sensors

When a guard sensor is triggered, the firmware disables the scanning of all other sensors except the guard sensor to prevent sensor false triggers.

 

Summary:

Hence in simple terms, the shield electrode is connected to the hatch fill around the sensor, and the guard sensor is a copper trace around other sensors. Shield electrode prevents false triggering in the presence of liquid droplets and the guard sensor detects a stream of liquid and prevents false triggering by disabling scanning in firmware.

 

CapSense component v7.0:

ncbs_3-1646483013405.png

Shield electrode in CapSense v7.0 component

The above picture shows the shield electrode option in the CapSense v7.0 version component. The shield electrode can be enabled in the CSD settings. This tab will be enabled only when the design contains at least one CSD sensor. The shield tank capacitor is enabled when the capacitance of the shield electrode is more than 100pF. This increases the drive capacity of the shield electrode driver. The pin for the shield electrode can be assigned in the Pins tab in Design Wide Resources.

 

Regards,
Nikhil

 

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3 Replies
Tim_Shih
Level 4
Level 4
50 replies posted 50 questions asked 100 sign-ins

I found there is another cap sense block in the PSoC creator (please refer to the attached file). This block has a shield pin, but I can't find this kind of cap sense block in the PSoC creator.

Thank you!

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ncbs
Moderator
Moderator
Moderator
50 likes received 250 sign-ins 250 replies posted

Hi @Tim_Shih.,

SHIELD:

In the presence of water droplets, C_LD (capacitance due to the liquid droplet) increases the capacitance of the system. The added capacitance draws an additional charge from the AMUXBUS. This gets reflected as an increase in the raw count and can contribute to a false trigger. Shield electrode will help us avoid false triggers in the presence of liquid droplets.

ncbs_0-1646482038845.png

C_LD contributes to false triggers.

 

Shield electrode is used for liquid tolerant operation. The shield electrode is driven by the driven shield waveform, which is the buffered in-phase version of the sensor waveform. 

ncbs_1-1646482179441.png

Driven shield signal is a buffered and in-phase version of sensor waveform

The hatch fill around the sensor is driven with this "driven-shield signal". The voltage on both sides of the liquid droplet remains at the same potential. Because of driven shield, the capacitance C_LD added by the liquid droplet does not draw any additional charge from the AMUX bus and hence the effect of capacitance C_LD is nullified.

ncbs_2-1646482403516.png

Shield overcomes the effects of liquid droplets

 

GUARD SENSOR:

When streams of liquid are present, the added capacitance will be much larger than that contributed by just a few water droplets, and hence the effect of the shield will be lessened. A guard sensor is a copper trace that surrounds all the sensors on the PCB. A guard sensor is similar to a button sensor and is used to detect the presence of streaming liquids. 

ncbs_0-1646483702732.png

Guard sensor as a copper trace present around other sensors

When a guard sensor is triggered, the firmware disables the scanning of all other sensors except the guard sensor to prevent sensor false triggers.

 

Summary:

Hence in simple terms, the shield electrode is connected to the hatch fill around the sensor, and the guard sensor is a copper trace around other sensors. Shield electrode prevents false triggering in the presence of liquid droplets and the guard sensor detects a stream of liquid and prevents false triggering by disabling scanning in firmware.

 

CapSense component v7.0:

ncbs_3-1646483013405.png

Shield electrode in CapSense v7.0 component

The above picture shows the shield electrode option in the CapSense v7.0 version component. The shield electrode can be enabled in the CSD settings. This tab will be enabled only when the design contains at least one CSD sensor. The shield tank capacitor is enabled when the capacitance of the shield electrode is more than 100pF. This increases the drive capacity of the shield electrode driver. The pin for the shield electrode can be assigned in the Pins tab in Design Wide Resources.

 

Regards,
Nikhil

 

Tim_Shih
Level 4
Level 4
50 replies posted 50 questions asked 100 sign-ins

Thank you so much!

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