Touch button products are widely used in more and more products due to their aesthetic appeal, ease of use, and easy cleaning. The scenarios in which they are used are also increasing, and the reliability of touch buttons in complex external environments is receiving greater attention.
This article focuses on the characteristics of Renesas products in dealing with noise, as well as some considerations in hardware and software design.
1
Touch Button Product Line and Noise Performance
Renesas has a wide range of touch button product lines, covering 16/32-bit, and 3 major core MCU products, providing customers with more options when selecting.
Click to view a larger image
The new CTSU2 product has features that enhance noise performance, such as multi-frequency scanning and active protection electrodes, which can support higher Level 4 IEC61000-4-3 and IEC61000-4-6 testing.
Click to view a larger image
2
Hardware Design
Good hardware design is the foundation for achieving high sensitivity and high reliability in touch buttons.Renesas provides the following application notes that clarify wiring requirements to achieve good ground noise and parasitic capacitance characteristics.
CTSU Capacitive Touch Electrode Design Guide
https://www.renesas.com/en/document/apn/capacitive-sensor-microcontrollers-ctsu-capacitive-touch-electrode-design-guide?queryID=c2371a86205358d1033cabfc285d4b40
Capacitive Touch Noise Immunity Guide
https://www.renesas.com/en/document/apn/capacitive-sensor-mcu-capacitive-touch-noise-immunity-guide-rev400?queryID=bca3f3e07dfd3ee80d79a05cf3fddf44
Additionally, in actual hardware design, to improve EMC characteristics, components such as ferrite beads may be added when necessary. The use of ferrite beads can reduce high-frequency power noise, but it can cause differences in noise characteristics of the power ground before and after the ferrite bead, so special attention should be paid to routing the grounds related to the touch button, TSCAP, and electrode protection to the same ground plane.
Click to view a larger image
3
Software Design
The reliability of touch buttons mainly depends on hardware design, but under certain hardware design conditions, software filtering can also enhance noise characteristics to some extent. Renesas provides a variety of software filtering options to cope with diverse noise environments.
Click to view a larger image
For example, under specific hardware conditions, EFT noise can exhibit significant periodic fluctuations.
Click to view a larger image
In the CTSU driver code, the following is used:
Moving Average (y[n]=3/4y[n-1]+1/4x[n]), which can apply to most random noise, but for this type of noise, due to its infinite impulse characteristics, it is affected by noise for a longer time and cannot be completely filtered out under high noise amplitude conditions.
Click to view a larger image
Therefore, in this case, it is recommended to use Median Filter, which can effectively filter out periodic, short-duration noise, aligning well with EFT noise characteristics and providing good filtering effects for EFT noise.
Click to view a larger image
Conclusion
Renesas touch buttons have a wide product line, and with unique noise-resistant features, they can provide first-class noise characteristics. In addition, comprehensive hardware and software design guidelines and technical support will further enhance the efficiency of touch button design.
Need Technical Support?
If you have any questions while using Renesas MCU/MPU products, you can scan the QR code below or copy the URL into your browser to access the Renesas Technical Forum to find answers or get online technical support.
https://community-ja.renesas.com/zh/forums-groups/mcu-mpu/
Recent Events Overview
1
Guangzhou, Beijing, Suzhou are waiting! Renesas Industrial Ethernet Technology Day seat reservation is ongoing
——Click to reserve and seize the technical frontier on April 9 in Xi’an
2
Embedded Systems – Renesas RA MCU Teacher Exchange Meeting – Nanjing
——Registration ends on March 28 (registration full cutoff)
3
Board Evaluation | RA4L1 Function Evaluation Event is now open
——Inviting you to explore the mysteries of RA4L1, registration ends on April 3
1
END
1
Recommended Reading
Achieving HMI Product Differentiation with the High Precision Low Power Touch Function of RX261/RX260
Making an Electronic Clock (Renesas RA) – Capacitive Touch Configuration
Video Tutorial | Introduction to RA Capacitive Touch QE
