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CapTIvate™ Touch Getting Started Manual
11
Copyright © 2021, Texas Instruments Incorporated
3
MCU selection and function evaluation
3.1
Determine sensor requirements
Before start the capacitive touch project using MSP430, please understand the selected
sensor type
,
the number
of sensors
, and
the occupied CAP I/O port
. Finally, select the appropriate MSP430 according to the corresponding
requirements.
At present, capacitive touch sensors are mainly divided into the following types: button/proximity sensor,
slider/wheel, and touch screen.
3.1.1
Button/Proximity Sensor
Both buttons and proximity sensors are zero-dimensional sensors. The principle of both implementations is the
same. The difference is that proximity sensing tends to have higher sensitivity and a larger sensor enclosing area.
Self-capacitive button:
From Figure 3-1, the self-inductive button is mainly composed of copper clad connected to the CAP I/O pins and an
insulating covering material. The button is also surrounded by a grounded copper clad separated by a ring gap.
Each button needs to occupy
1
MCU CAP I/O pin.
Figure 3-1 Self-capacitive button PCB diagram
Mutual-capacitive button:
In applications that require a large number of buttons, capacitive sensors can be arranged in a matrix, each button
will be connected to two CAP I/Os, and one CAP I/O will be connected to a row or column of buttons. As shown in
Figure 3-2, the two box-shaped copper clad inside and outside are Tx and Rx. The program supports multi-button
touch. X row * Y column buttons need to occupy
X+Y
MCU CAP I/O pins.
Figure 3-2 Mutual-capacitive button matrix PCB diagram
Self-capacitive proximity sensor:
Usually, the proximity sensor chooses the self-capacitive scheme. The main reason is that it has a longer detection
distance than mutual-capacitive scheme, more flexible wiring and structure, and higher signal-to-noise ratio. The
PCB outer circle in Figure 3-3 shows the proximity sensor. In addition to using PCB copper to form a proximity
sensor, wires or even conductive metal structures can also be selected. A self-inductive proximity sensor needs to
occupy
1
CAP I/O pin.
