Instrument Cluster Design for Electric Vehicles with Renesas RL78

Arun Kumar V
30. September 2021 · Write a comment · Categories: ARM, Embedded Hardware, Embedded Software, Sparklet GUI Library

In any vehicle, the instrument cluster forms a critical part as it is the face of the vehicle that reflects the current state. Apart from providing the basic vehicle information, it can also provide crucial indications of electrical component malfunctions (EFI /ISG related). Clusters can acquire vehicle data over simple mechanisms such as encoders as well as through complex interfaces such as CAN, SAEJ1850 etc.,

Instrument cluster design for electric vehicles may have less system complexity, but they have to be more user friendly, less power hungry, and a cost-effective solution. Careful design and choice of cluster components is necessary to meet the stringent compliance requirements. Of the constituent components, the MCU holds the major stock whereas only a few vendors will be supporting automotive grade with the desired feature sets.

Renesas RL78 is an ultra-low power microcontroller (MCU) that enables customers to build compact, energy efficient instrument clusters for a wide range of two-wheeler and four-wheeler vehicles. It offers highly suitable peripheral interfaces such as: Three Channels of Stepper Motor Controller, LCD controller, Multiple IOs etc.,

In this blog, we will discuss in detail about the various features of an instrument cluster and how RL78 MCU will help simplify the design.

Instrument Cluster Subsystem

The major components and their functionalities are as follows:

Gauges: Generally, three gauges namely RPM, Temperature and Fuel Level get indicated by the cluster.
- Fuel Gauge: The Fuel gauge ranges from Empty (E) to Full (F). Typically, the Fuel sensor unit is a TSR /SMR type realized with components such as float with potentiometer, Adjustable arm and sending unit with two wires (signal & ground wire). The signal received from the fuel sensor is analog. The pointer position depends upon the incoming resistance value and indicates the vehicle’s fuel level.
- RPM Gauge: The signal received from the RPM sensor from encoder such as tach terminal unit with signal & ground wire, fire wall grommets is treated as frequency input. Based on the type and top speed of the vehicle, the input range varies.
- Temperature Gauge: The signal received from the temperature sensor is also analog. Realized with sensors such as protective rubber unit, thermistor with two wire. Front end circuit converts the input resistance to corresponding voltage and thereby the voltage value at the microcontroller input indicates the current engine temperature.
- Seven Segment Displays: Clusters may have different type of segmented display with various resolutions such as 27 X 4, 39 X 4, 48 X 4, 53 X 4 and 54 X 4. These could indicate information such as odometer, trip distance, hour meter etc.,
- Telltales: Telltales are sort of regulatory indications typically realized with LEDS required to show the state of various components such as low battery, engine faults, high beam etc. They are usually realized via onboard LEDs with mechanical light guide. Graphical overlays will also be placed over the guides with standard Tell tale signs.
- Switches: Usually a single switch or simple rotatable push-type switches are available to manipulate the information shown in the display such as Trip distance, Time etc.

There could be variations in the offerings and feature set based on the vehicle manufacturer.

RENESAS RL78 for Cluster:

Renesas is a leading semi-conductor company in the automotive space offering cluster solutions for many decades. While there are some architectural differences between all the MCU’s of the Renesas RL78 family, the sub-system remains more or less the same. The high-level design of the RL78 MCU based instrument cluster is captured below:

Instrument Cluster - Block Diagram — Instrument Cluster – Block Diagram

RL78 series of MCU’s help realize vehicle clusters effectively with its feature rich peripherals set:

Microcontroller: The RL78 MCU helps in achieving the highest performance within the low end MCU space. It offers improved efficiency, extensive scalability and reliable safety functions that aid in developing energy efficient instrument clusters. It has an operating voltage that ranges from 2.7V to 5.5V and flashes the program using 80 microcontroller pins.

Stepper Motor Drivers: There are up to three channels of stepper motor controllers / drivers with zero-point detection that can be configured using PORT pins (Sin+, Sin-, Cos+, Cos-). Each channel is controlling a stepper motor dedicated to gauges which commands the motor to move and hold at one of the angles without any position sensor. With the help of software based PID control, it is possible to effectively control the needles.

Segment LCD Controller: Capable of driving up to 200+ segments, the in-built LCD controller is available for controlling the segmented display with various resolutions such as 27 X 4, 39 X 4, 48 X 4, 53 X 4 and 54 X 4 which is directly driven from the RL78 microcontroller. The LCD screen can be controlled by the software to display any kind of data dynamically such as TRPI information, hour meter data etc.

Multiple IOs: There are multiple analogs and digital IOs available for interfacing sensors and Tell-Tale LEDs. RPM, temperature, and fuel level sensors are interfaced via a suitable front-end circuit. If needed, various Tell-Tale LEDs such as turn left, turn right, service, brake, etc. can be driven with dedicated digital outputs.

Analog Input Gauges: RL78 series comes with a rich set of ADC inputs that can be used to convert resistance/voltage-based sensor inputs to digital values. Software based processing will increase the accuracy of the acquired value.
Encoder inputs: With up to 24 timers, RL78 can be used to measure a variety of encoder inputs such as RPM, perform custom processing and obtain accurate digital values.
External connectivity: RL78 can also support I2C/SPI interfaces that can be used to communicate with peripherals such as EEPROM where the accumulated vehicle information such as ODO, TRIP data can be stored. RTC can be interfaces to track real time.

Variants of RL78 also offers sound generator which can set a volume level and tone frequency, two channels of CAN, and expanded flash memory/RAM up to a maximum of 512 KB/24 KB, suitable for low-end instrument cluster applications.

Embien’s Expertise in the Automotive Industry:

Embien Technologies is a leading embedded systems development company that specializes in high – tech product engineering services. We help clients take competitive lead in their markets. With a unique mix of innovation, technology, and quality, we offer cutting-edge automotive electronics system designs by adapting the latest technologies in clusters, diagnostics, infotainment, connectivity etc., With deep domain expertise, we have assisted several OEMs, Tier 1, and Tier 2 vendors to surge their automotive electronics such as Instrument Clusters (Heavy & Light- Duty Vehicles), Digital Cockpits etc., by integrating sensors & radars, network connectivity, path planning & mapping technologies. Do you have a design idea in mind? Then, get in touch with us today!

Intel Cyclone V FPGA GUI Application Development

Saravana Pandian Annamalai
30. May 2017 · Write a comment · Categories: Embedded Software, Sparklet GUI Library, Technology

Embien has been working on various types of embedded systems including those powered by FPGA’s for a variety of applications. Of late, there are a lot of requirements for GUI Application development on FPGAs for user interaction. In this blog, we introduce our Sparklet embedded GUI library along with our Flint FPGA UI Interface Editor for enabling FPGA for graphics. Also Sparklet running on a Linux powered Intel Cyclone V SX SoC FPGA is demonstrated with a Terasic DE1-SoC-MTL2 kit.

FPGA GUI Application Development

Modern FPGA’s have a multitude of IPs to handle different peripherals interfaces. Most of these FPGAs, called SoC FPGAs have an internal microcontroller core as a hard IP around with LEs are placed for configuration and customization.

Such a design warrants a powerful user interface for communication with the user for a seamless experience. Full fledged Intuitive GUI application development ecosystem is the need of the hour to enable a faster time to market. Developers need to dedicate their effort on FPGA and internal logic developments rather than working on nitty-gritty of FPGA GUI application development.

Sparklet – embedded GUI library is the right fit for such a FPGA based GUI development. Written purely in ANSI C, Sparklet can be ported across platform with minimal effort. The GUI Application development can be done using our Eclipse based Flint tool that supports Windows based emulation as well. The FPGA UI Interface Editor tool generates ‘C’ source files and headers that can be compiled in to the project to get a fully working application within a very short time.

Sparklet being a very modular and extensible design, it is also possible to take advantage of the Graphical acceleration engines with Sparklet to improve the rendering speed and quality.

Sparklet GUI on Intel Cyclone V FPGA

This demo of the Sparklet GUI library runs on a Intel Cyclone V SX SoC FPGA. Some of the salient features of the FPGA include

Dual-core ARM Cortex-A9 (HPS)
85K programmable logic elements
4,450 Kbits embedded memory
Fractional PLLs
Hard memory controllers
Multiple display interfaces
Multiple USB Host interface
Ethernet, UARTs, ADCs etc

The development kit from Terasic, DE1-SoC-MTL2 includes a DE1-SoC development board targeting Altera Cyclone® V SX SoC FPGA, along with a capacitive LCD multimedia color touch panel which natively supports five points multi-touch. The display is a 7-inch TFT LCD with pixel resolution of 800*480 and color depth of 16 million colors (8-bit RGB) along with a LED backlight.

For such an FPGA based design, the underlying software can be designed with any of the following architectures:

Without an OS
With a minimal RTOS
With full fledged OS like Linux

Sparklet, providing design flexibility, is suitable for use with each of these approaches. The below demo showcases Sparklet running on top of Linux OS.

Though none-of the underlying Graphical engine features are not used in this case, it is possible to do so using the hardware acceleration engine changes.

Thus Sparklet along with Flint makes FPGA GUI application development a lot easier and enables developers work on core functionality there by reducing overall product development time.

About Embien: Embien Technologies is a leading service provider in the Embedded software domain. Our team has rich experience in working with various OS like Linux, Android, Windows CE, FreeRTOS, uC-OS, QNX etc. Learning from our experiences in various application domains, we have conceptualized and created the Sparklet Embedded GUI tool that can be used to develop UI’s faster and smaller.