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Technical Article

Don’t Compromise Your Capacitive Touch Design

Benjamin Moore
A major challenge for developing capacitive touch interfaces is managing design trade-offs. An appropriatebalance of features such as low-power operation, noise immunity and response time must be made whendeveloping capacitive touch products. Capacitive touch thermostat user interface TI Designs reference designshows you how to optimize this balance for line powered and battery powered use cases. These two use cases
are commonly found in building automation applications.

Products that are designed to be line powered—wall-mounted controllers— must use a capacitive touch solution
with noise immunity features to ensure proper behavior in electrically noisy environments. Unfortunately, thisoften comes at the cost of higher power consumption, and products that are intended to be battery powered—remote control— will often need to sacrifice some noise immunity features in order to achieve an ultra-low-power
profile. In both cases, the solution must use an appropriate sensor measurement rate and filtering to provide afast response time for the best user experience.
To solve these problems, the Capacitive touch thermostat user interface TI Designs reference design uses aMSP430™ microcontroller (MCU) with CapTIvate™ technology and meet the needs of both use cases. It alsouses FRAM technology to store critical variables that define the application state. This enables the design tomaintain a low-power profile and seamlessly retain its application state through power-loss.
Thanks to the communication module in the CapTIvate technology Software library, the design provides a simple
solution for integrating capacitive touch technology with a LCD display. A demo is included with the reference
design that demonstrates how the communication module can be used to connect a MSP MCU with CapTIvate
technology with a host processor over a I2C interface. The demo uses an MSP430FR2633 MCU with CapTIvate
technology and a MSP430FR4133 MCU with an integrated LCD driver to create a complete, low-power, FRAM
thermostat design.
A summary of the specific design issues related to capacitive touch development that are addressed by theCapacitive touch thermostat user interface TI Designs reference design can be found below:•••••

Meeting electromagnetic compatibility (EMC) standards at the commercial product level with layout
techniques, frequency hopping, and a multi-frequency processing algorithm
Providing more than a year of lifetime on AAA batteries with a low-power profile
Using FRAM to retain application state through power-loss
Developing a capacitive touch interface with a dedicated capacitive touch controller, a host processor and aI2C serial communication interface
Create a design that uses software for various switch implementations, such as momentary and maintainedswitches

SSZTBU2 – DECEMBER 2015
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Don’t Compromise Your Capacitive Touch Design
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Visit the below links to learn more about Capacitive touch thermostat user interface TI Designs reference design:•••2Download a detailed design guide
Learn more about MSP430 MCU with CapTIvate technology
Buy the CapTIvate MCU development kit

Don’t Compromise Your Capacitive Touch Design
Copyright © 2023 Texas Instruments Incorporated

SSZTBU2 – DECEMBER 2015
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