Capacitive Touch and Segment LCD Control: Renesas Releases MCU for Smart Appliances

The design of modern smart home appliances and IoT devices often centers on creating an intuitive, display-based human-machine interface (HMI) while maintaining strict low-power budgets. Renesas has addressed these requirements with the introduction of the RL78/L23 microcontrollers (MCUs), an expansion of the company’s RL78 product line. These new, 16-bit MCUs are engineered to balance performance with power efficiency by integrating key peripherals for LCD control and capacitive touch sensing.

The RL78/L23 MCU combines an ultra-low-power RL78-S3 CPU with integrated peripherals for LCD control and capacitive touch sensing. Image used courtesy of Renesas

Minimal Energy Draw in Operation and on Standby

At its core, the RL78/L23 MCU features an RL78-S3 CPU and operates up to 32 MHz. The MCU is optimized for ultra-low power consumption, a crucial characteristic for battery-powered devices. It has an active current of 109 μA/MHz and a standby current as low as 0.365 μA, with a fast 1 μs wake-up time to minimize active-mode duration. To further reduce power, a SNOOZE Mode Sequencer handles dynamic LCD segment display without CPU intervention, minimizing wake-ups. According to Renesas, a new VL4 reference mode for the LCD controller reduces operating current by approximately 30% compared to previous RL78/L1X MCUs.

To get started with the RL78/L23 MCUs, developers can utilize Renesas’ RL78/L23 fast prototyping board, compatible with Arduino IDE. Image used courtesy of Renesas

Segment LCD Display and Capacitive Touch

The RL78/L23 MCUs integrate a segment LCD controller capable of supporting up to 56 segment and eight common signal outputs. Alongside this, a capacitive touch sensing unit (CTSU2La) supports up to 36 channels, enabling sleek and responsive user interfaces. The devices also include a new IH Timer (Timer KB40) designed for precise multi-channel heat control, a feature particularly relevant for smart kitchen appliances like induction cooktops and rice cookers.

The RL78/L23 also features a dual-bank flash memory architecture, with up to 512 KB of flash memory. This configuration allows for seamless firmware over-the-air updates, where one bank can run the user program while the other receives an update, which is essential for applications where downtime must be minimized, such as smart meters. Additionally, the MCUs offer a wide operating voltage range from 1.6 V to 5.5 V, which allows for direct operation from common 5 V power supplies in home appliances, reducing the need for external voltage regulators.

Renesas’ RL78/L23 capacitive touch evaluation system for testing and validation. Images used courtesy of Renesas

Support and Development Ecosystem

To support the new RL78/L23 MCUs, Renesas offers a comprehensive development ecosystem. The RL78/L23 fast prototyping board is an evaluation board designed to accelerate initial prototype development. It is equipped with the RL78/L23 MCU and includes a built-in emulator, eliminating the need for a separate debugging tool. The board features an LCD panel and two touch buttons, allowing engineers to begin evaluating the MCU’s core capabilities immediately. It also supports standard interfaces like Arduino Uno, Pmod, and Grove, providing a flexible platform for adding various sensors and communication modules.

The RL78/L23 capacitive touch evaluation system is a specialized evaluation system for the capacitive touch function. It allows developers to evaluate various touch functions, including buttons, wheels, and sliders. The kit is designed to work with Renesas’ QE for Capacitive Touch software, which provides a graphical user interface to simplify the process of adjusting sensor sensitivity and automatically generating source code. This kit’s focus on the capacitive touch feature makes it a targeted tool for engineers developing HMIs where touch functionality is a central design element.