Capacitive Touch BoosterPack Hardware
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3.2
Capacitive Touch Sensors
The six different capacitive touch sensor areas are connected to the Port 2 of the device. On the MSP430
Value Line devices with enabled touch-sense, Port 2 I/Os have no analog functionality. These I/Os also
have a smaller internal capacitance than Port 1, which make these them more sensitive than the
capacitive touch sensors on Port 1.
Figure 9
shows the connection of the capacitive touch sensor areas to the MSP430.
Figure 9. Capacitive Touch Sensor Areas
To enable the touch-sense feature of the I/Os, set the secondary port select PxSEL2 and clear the PxSEL
bit. The selected pins start oscillating immediately, and the frequency is a direct indication of the
capacitance connected to the port pin. The touch-sense I/Os oscillate within a frequency range of 1 to 2
MHz, which is strongly dependant on the supply voltage, the device package, and environmental
influences. For more information about the touch-sense feature of the Value Line devices, to download
code example, or to find application examples, go to the Capacitive Touch BoosterPack wiki page
(
http://processors.wiki.ti.com/index.php/MSP430_LaunchPad_(MSP-EXP430G2)
) or get the MSP430
Capacitive Touch Sense Library (
http://focus.ti.com/docs/toolsw/folders/print/capsenselibrary.html
), which
is used in the application demo included in this kit.
NOTE:
The Capacitive Touch BoosterPack hardware can also be used with other MSP430 devices.
Resistors R10 to R15 must be populated with a resistor to realize a RC discharge that can
be measured with a timer.
16
430BOOST-SENSE1 - Capacitive Touch BoosterPack for the LaunchPad
SLAU337A
–
April 2011
–
Revised September 2011
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