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# Are CSX and CSD methods feeding AC or DC to the sensing elements?

Hi all,

simple question, I could not find the info in the datasheet/design guideline for capsense 4 and 6. Are the CSX and CSD methods driving the sensor electrodes with AC or DC current?

I know CSX is probably AC as it checks for variations of current through Cm.

Thank you!

1 Solution
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6 Replies
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# Re: Are CSX and CSD methods feeding AC or DC to the sensing elements?

The CSX and CSD methods driving the sensor electrodes with  DC current.

CSD:

A resistor that is formed by switching a capacitor between a voltage and ground, equals 1/(Fs * (Cx + CF)).

CSX:

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# Re: Are CSX and CSD methods feeding AC or DC to the sensing elements?

Thank you for your reply! Then I do not understand why there is a AC source symbol at the entry point of the Tx electrode in figure 7-32 of the capsense design guide

I thought this ac source was part of the capsense module in the psoc?

Also, I have made this post on electronics stackexchange for further understanding and the answer by user Voltage Spike mentioned the mutual capacitance used AC measurements. were they wrong about this?

The middle conductor will be floating at DC, but touch sensors are AC measurements so DC doesn't really matter.

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# Re: Are CSX and CSD methods feeding AC or DC to the sensing elements?

the CSX supply the DC current, then through a switch, after the switch which supply for Capacitor is AC. The principle you can refer to the first reply.

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# Re: Are CSX and CSD methods feeding AC or DC to the sensing elements?

1. I am struggling to understand the schematic. it is real AC or just a square wave from the switches??and is it of amplitude VCC?

2. So the principle really is to measure the delta AC current moving through TX, through the finger, to device ground, vs current reaching normally RX

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