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The limitation of capsense is we can not detect finger press at the start up that is when the capsense board is powered up and a finger is already present then it won't be able to detect unlike mechanical switches. So, what are the possible methods to make capsense work in such conditions?
Method #1: By knowing the approx. difference between the raw counts (without finger) of buttons in advance and then using this to detect the finger press at the start up. Limitation: It won't be able to detect if both the buttons are pressed.
Method #2: Instead of using the physical button, use a dummy sensor which will be placed in software not in hardware. Then applying the above mentioned method.
Method #3: Instead of detecting the finger press, detect the finger release. Whenever the finger will be released the baseline will snap down to a lower value. If this difference is greater than finger threshold then it can be inferred as that there was a finger press. Limitation: We need to decide the time that till when we are going to check this baseline.
Is there any other idea?
It is possible to check finger press on power up in CapSense Express device also.
Normally CapSesne Express device are used with Host controller. Host controller can read the register and compare the raw count of different buttons to check finger press on power up. It is prerequisite to have both button size same, so in normal condition they give same raw counts.