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Sensing Technologies

PeMa_1184626
New Contributor

On the board I designed, two  MBR3116 are fitted to support 18 buttons. Each group of 9 buttons ( 3 row x 3 column)  is surrounded by its corresponding shield. Keypad is 3 row x 6 x column

The distance between buttons is 22 mm and the buttons diameter is 12 mm.  There is a GND trace separating two shields to prevent cross-talk.

I would like to include Guard sensor. If I select rectangle loop for Guard,  I cannot run two Guard traces plus shield and GND tracks between grouped sensors as 22 mm spacing is not enough.

I have two questions;

1) Does Guard sensor have to be a loop? Can I use 'C' shape around left group of buttons and mirrored 'C' around the right group?  

2) When the Guard sensor is scanned, is the shield active or disabled? In other words, Guard is dealt with same as any other button?

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Hari
Moderator
Moderator

Hello PeMa_1184626

1) Does Guard sensor have to be a loop? Can I use 'C' shape around left group of buttons and mirrored 'C' around the right group?

-> No, Guard sensors need not be a complete loop. You can use a 'C' shaped outline around the sensors and this will work

2) When the Guard sensor is scanned, is the shield active or disabled? In other words, Guard is dealt with same as any other button?

-> Yes, shield will be active and a guard sensor is dealt with the same way as any other sensor.

Best regards

Hari

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Hari
Moderator
Moderator

Hello PeMa_1184626

1) Does Guard sensor have to be a loop? Can I use 'C' shape around left group of buttons and mirrored 'C' around the right group?

-> No, Guard sensors need not be a complete loop. You can use a 'C' shaped outline around the sensors and this will work

2) When the Guard sensor is scanned, is the shield active or disabled? In other words, Guard is dealt with same as any other button?

-> Yes, shield will be active and a guard sensor is dealt with the same way as any other sensor.

Best regards

Hari

View solution in original post

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PeMa_1184626
New Contributor

Thank you Hari, I also could assume the Guard sensor would not act like an antenna ( C shape vs closed rectangle). Even if it does, the 560R and input capacitance of the MBR31116 would filter high frequencies. Is this assumption correct?

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Hari
Moderator
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Hello PeMa_1184626

Yes. The 560 ohm series resistor that is placed will result in damping the waveform coming from the pin and will smooth out the sharp edges of the waveform. This will result in lower emissions from the device.

Note: It is recommended to place the series resistor close to the IC (within 10 mm) so that the waveform is damped at the source itself.

Best regards

Hari

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