Touch sensitive switches are found in a variety of consumer products including home appliances, MP3 players and cell phones. A touch sensitive switch is a switch that is implemented as a trace on a printed circuit board. The architecture of the trace creates a capacitive element. Touching this trace with a finger creates a change in capacitance, which is detectable using a variety of techniques. Silicon Labs' capacitive touch sense solution uses the switch capacitor as part of a simple RC (resistor-capacitor) relaxation oscillator. The C8051F9xx family includes enhanced comparators which enable touch sense capability without any external components, but the solution can be implemented with any Silicon Labs MCU that has a standard comparator.
A capacitive touch sense solution is easily implemented on many Silicon Labs MCUs and offers many advantages including a low BOM cost, small Flash requirements (less than 400 bytes), little MCU overhead, low power requirements and does not require the MCU to use a precise voltage source. In terms of hardware peripherals, only a comparator and timer are required, which leaves many resources available for the rest of the system.
The sensitivity of the switches is also easily configurable in firmware which enables two useful features. The first is that by increasing the switch sensitivity, the switches can be used for proximity detection as well as being used as a standard switches. Second, the configurable sensitivity makes the switches easy to use with a variety of materials covering the PCB, such as plexiglass, glass, or various plastics.
The following MCU families can support capacitive touch sense. The number in the switches column indicates the maximum number of switches the can be directly interfaced by the MCU. Additional switches can be supported using an external multiplexer.
* Denotes maximum value in family
 Capacitive Touch Sense Application Note (AN338)
Capacitive Touch Sense Example Firmware (AN338SW)
Capacitive Touch Sense Starter Kit and Daughter Card
 The Capacitive Touch Sense Daughter Card includes four capacitive touch sense pads to enable customers to develop applications implementing capacitive touch sense switches. The Capacitive Touch Sense Starter Kit includes a Capacitive Touch Sense Daughter Card, ToolStick Base Adapter and USB cable. The Capacitive Touch Sense Daughter Card is also available individually for customers that already have a ToolStick Starter Kit.
Capacitive Touch Sense ToolStick Daughter Card User's Guide
 Capacitive Touch Sense Starter Kit
Capacitive Touch Sense Daughter Card
 The daughter card is pre-loaded with a game that requires you to mimic LED light sequences by entering the sequence via the capacitive touch sense pads.
Light Sequence Game
C8051F336 Development Kit
The development board in the C8051F336DK includes a Capacitive Touch Sense switch and example code. The development board provides an easy way to evaluate the solution.
C8051F336DK
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