captivate query

Dear Savinay,

1. Generally speaking there is no minimum electrode capacitance for a reliable working of captivate. In theory, the smaller the electrode capacitance the greater relative change is achieved by a touch. This is difficult to achieve because of the relationship between the area that couples to circuit ground and the area of interaction with a human finger – it is difficult to increase one without increasing the other. Another important consideration is noise immunity and one basic way to address this is to increase the capacitance of the electrode with a discrete capacitor. In this sense a minimum capacitance may be required to achieve a desired level of immunity. An example of this can be seen in www.ti.com/.../tiduav1.pdf.

2. The value of LTA and count may give some insight. It is possible to have an insensitive system. This would typically mean that the settings for conversion count and conversion gain are equal and the value itself is relatively low. Since offsetTap is zero this also suggests that the numbers are the same. Additionally, there are also filters on the LTA and count that may be masking the touches depending upon how quickly you touch and release the element. If you start increasing the conversion count relative to the conversion gain you should see more offset applied and the change in counts associated with a touch increase.

3. In simplest terms the coarse and fine gains are used to achieve the conversion gain and the offset is added after the gain is established to achieve the resulting conversion count. The graphic in this section also highlights sensitivity as a function of gain and count. software-dl.ti.com/.../ch_tech.html

Regards,
Chris

Dear Savinay,
Please let me know if you have additional questions. Since this thread has been idle, I will close.

Thanks and Regards,
Chris

Thanks . I have no further query

Regards

savinay