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issue: May 2008 APPLIANCE Magazine

Sensors and Microcontrollers
A Sense of Sophistication

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by Jill Russell, Contributing Editor

Highly developed sensor systems and more-capable microcontrollers are satisfying functional safety standards and providing better energy efficiency capabilities.

BSH Home Appliances’ Thermador brand (www.thermador.com) launched Masterpiece Deluxe series cooktops with Sensor Dome infrared sensor technology in 30- and 36-in. cooktops. The 30-in. features four burners
and one sensor, while the 36-in. features either five burners with one sensor or five burners with two sensors. The sensor, in the form of a retractable dial, uses an infrared beam to continually measure the heat from the cookware. The sensor continuously cycles the burner on and off, or shuts it off completely to maintain a specific temperature and prevent pots from boiling over.

The company says the sensor technology works in conjunction with its CookSmart program that provides nine preprogrammed settings to cook a variety of foods, including pasta, vegetables, and deep-fried items. Besides advanced sensors, the cooktops also come equipped with a trapezoid-shaped touch control panel that operates at 17 different power levels, including a warming function.

Recent standards that impact sensors and microcontroller (MCU) systems are intended to keep end products safe. ANSI UL 1998, Standard for Software in Programmable Components, and IEC 61508, Functional Safety of Electrical/Electronic/Programmable Electronic Safety Related Systems, help ensure safety functions are considered during product development and engineered into the final design.

The International Electrotechnical Commission (www.iec.ch) recommends OEM engineers conduct a hazard analysis to determine if functional safety is a necessity in the end product to provide protection against an operational hazard. If other aspects of the design of the appliance do not eliminate those potential hazards, EC 61508 defines means of achieving functional safety. The “safety-related system” is the hardware, the software, and even the human-element part of a safety function—IEC wants engineers to consider the system as a whole. Systems could be emergency shutdown functions, fire and gas control systems or gas burner management, or even an “information-based decision support tool” where a bad choice by the user might result in a hazard.

“Design engineers today are required to complete engineering projects in a limited amount of time. They need to learn about the MCU’s architecture and its development tools, gain experience in motor control technology, develop a hardware platform, and then write the software for a new product,” says Ritesh Tyagi, director of the system LSI business unit at Renesas Technology America Inc. (San Jose, CA, U.S.; www.renesas.com). “Our R8C25 MCRP makes it easier for engineers to quickly turn their ideas into action, while minimizing the risk in the development cycle. This platform provides a complete solution for implementing and developing BLDC motor control by offering both proven hardware and control-algorithm software.”

The R8C/25-based BLDC (brushless dc) motor control reference platform (MCRP) enables engineers to quickly develop motor control to appliances while providing performance, reliability, and power efficiency to these systems. An R8C/Tiny microcontroller (MCU) at the heart of the reference platform handles different BLDC motor control algorithms. Key to the hardware reference platform is adaptability, and the platform supports four algorithms: 120˚ trapezoidal Hall-sensor-based BLDC motor control; 180˚ sinusoidal Hall-sensor-based BLDC motor control; 120˚ sensorless (back-EMF)-based BLDC motor control using external comparators; and 120˚ sensorless (back-EMF)-based BLDC motor control using the MCU’s on-chip A/D convertors.

“Consumers’ expectations for high-end and intuitive user interfaces are driving the need for better touch and display technologies in everything from blenders to ovens,” Mike Ballard, manager, Home Appliance Solutions Group for Microchip Technology Inc., tells APPLIANCE magazine. “Also, with the recent additions of innovative features in appliances, new sensors are required to provide the system that enables proper appliance operation.”

Compact Chips

Microchip (Chandler, AZ, U.S.; www.microchip.com) says its PIC10F family of 8-bit microcontrollers helps do the trick. “With ever-expanding electronic control in home appliances, additional sensors are required for proper system operation. Often these sensors are located outside the main electronic control board. Typically, only a simple electronic control is required to either linearize a sensor’s inputs or provide a simple serial communication to the main control board,” Ballard explains. “In these situations, a very small, ultra-low-cost MCU is all that is required.”

The company’s answer was a sensor that measures 1.5 by 2.9 mm, is Flash-based, and is cost-effective. The PIC10F family is designed to be the world’s smallest Flash-based MCUs, with Flash sizes of 375 or 750 bytes and equipped with on-chip analog-to-digital convertors and an internal oscillator. They operate from 2 to 5.5 V. Additionally, Microchip’s line of PIN16F 8-bit Flash MCUs was designed for use with general household appliances (e.g., blenders, refrigerators, and dishwashers), consumer electronics, commercial applications, and HVAC controls. The latest MCUs operate from 1.8 to 5.5 V, and have 14 analog-to-digital convertor channels and an internal oscillator. The increased flexibility allows OEMs to integrate higher levels of sophistication and functionality in their products at a low cost.

Microchip’s new 8-bit flash PIC MCUs are well suited for appliance applications such as blenders, refrigerators, dishwashers, cell phones, electric shavers, vacuum cleaners, and HVAC. The PIC16F72x MCUs operate between 1.8 and 5.5 V and a 16 MHz oscillator is said to make conditional event counting and measurements easier. They increase design flexibility through an ability to interface with external devices such as environmental sensors, and they provide additional system control and monitoring.

Microchip is also helping OEMs achieve faster implementation with software and programming tools. Its PICDEM Touch Sense 1 Demo Board helps with capacitive touch sensor implementation. The board comes with an analyzer and software that enables designers to evaluate the capacitive touch-sensing capabilities of their applications. The mTouch Sensing Solution software is Windows-based and provides a resource library, source code information, and support materials to help reduce development time and cost.

Renesas Technology America Inc. (San Jose, CA, U.S.; http://america.renesas.com) is providing powerful MCUs in tiny packages for motors. The company’s R8C/25-based brushless dc (BLDC) Motor Control Reference Platform (MCRP) is able to handle various types of sensors, including Hall, encoders, resolvers, and tachometers. The MCUs can handle various BLDC control algorithms to balance cost, performance, and function. The MCU supports four algorithms with a simple two-layer printed circuit board, while LEDs provide a visual indication of switching patterns for ease of use. The MCUs come with a PC-based software package that is programmed using a graphical user interface (GUI).

“The ability to handle a multitude of sensors with a single MCU is one of the critical factors for engineers. The R8C family has dedicated timers that can handle interfacing requirements for extracting speed, position, and velocity information directly from the sensor with minimal processor overhead,” explains Ritesh Tyagi, director of Renesas’s System LSI business unit. “The benefits to appliance designers are reduced software complexity, relaxed processing requirements, and better utilization of the CPU in managing critical system functions.”

Today physicians require electronic measurement to monitor gas flow for increased accuracy and reliability, and to capture an accurate treatment log. The MEMS flow sensor from Omron Electronic Components (Schaumburg, IL , U.S.; www.components.omron.com) has bypass setup, similar to a differential pressure sensor, which is an indirect method of measuring gas flow. The MEMS mass flow sensors, however, deliver a higher level of resolution at very low flows when compared with differential pressure (dP) sensors. The D6F-P series can have both bidirectional and unidirectional flow calibrations, with a negative flow indication on the unidirectional version. The series features an integrated dust segregation system that uses symmetrical centrifugal flow paths to keep particulate matter away from the flow sensor element regardless of flow direction.

Freescale Semiconductor (Austin, TX, U.S.; www.freescale.com) also offers a family of 8-bit MCUs to help reduce costs and expand performance options for large appliances, including washing machines, dishwashers, refrigerators, and cooking appliances. The three S08AC MCUs offer 60K, 48K, and 32K Flash memory and facilitate energy and water conservation in the end products. Analog-to-digital convertors help control motor operation to allow for shorter washing cycle times in washing machines and dishwashers. The MCUs also meet the IEC 60730 regulation and offer enhanced software safety functions for automatic controls, such as the wash cycles for a washing machine.

Freescale is striving to offer OEMs more complete solutions and recently teamed with control valve supplier Microstaq to enhance a microelectromechanical silicon expansion valve with its sensor technology. Freescale’s pressure-sensing and control technology works with the valve to control HCFC and HFC refrigerants in air-conditioning and refrigeration equipment. Freescale says the valve helps improve operation and reliability, and enables predictive system maintenance.

In order to help OEMs program several functions on one printed circuit board (PCB), Cherry GmbH (Auerbach, Germany; www.cherry.de) released its SKM LC. The single board enables cooktops to provide a heat boost feature, operating-time limits, child lock, alignment for use with infrared sensors, automatic sensor calibration, and error codes. An alarm function and additional burner zone can be added for advanced product features. Horizontal and vertical installation capabilities add an element of design flexibility. The supplier says the board can be an economical replacement for traditional rotary selectors and a cost-efficient way to provide premium technology and features to cooking appliances.

GE Sensing and Inspection Technologies, part of GE Enterprise Solutions, launched the ChipCap as a next-generation humidity and temperature sensor. The sensor is designed to cut sensor integration costs in half while measuring relative humidity and temperature for white goods, HVAC, medical, and other appliances. GE says it can cut costs and, thus, the product development cycle, so drastically because the sensor is fully calibrated in the factory, so OEMs don’t need to adjust the sensor themselves. That can cut out the $30,000-to-$50,000 cost for calibration equipment.

“[ChipCap] doesn’t require further signal conditioning, therefore reducing the overall design time in integration, and time to market for new products,” said Bryan Conner, global product manager, Gas & Moisture for GE Sensing & Inspection (Billerica, MA; www.gesensing.com). “By eliminating the need for calibration, end-users increase throughput and lower cycle time once in production.” The sensor offers both digital and analog modes on one chip at 5 V dc, and can be used from 0 to 100% relative humidity and –50° to 150°C in condensing environments.

STMicroelectronics increased the on-chip Flash capacity of its STR91xFA ARM966E-S–based MCU family with 1.1-Mbyte and 2.1-Mbyte variants
to deliver higher memory density than other
ARM9- or ARM7-TDMI–based standard MCUs.
The new devices are pin- and function-compatible with existing 288-KB and 544-KB versions in LQFP-80, LQFP-128, and BGA-144 packages, allowing engineers to scale designs easily without expensive circuit board changes.

Engineers can use the MCUs to build more-complex embedded functionality using on-chip memory, adding security against piracy as well as saving board space and bill-of-materials costs. The units are designed to be a single-chip solution, with integrated Ethernet, USB, and CAN interfaces; a 10-bit ADC; multiple timers; and up to 80 5-V-tolerant general-purpose I/Os.

Safe Sensors

The latest safety regulations are also affecting sensor and MCU capabilities. “Regulations like the 1988 and IEC 60730, memory capacity will increase to support the additional safety features required,” says Ray Shin, engineering manager, MCUs, for NEC Electronics America (Santa Clara, CA, U.S.; www.nec.com).

The company believes the future of sensors depends on the components’ ability to easily and seamlessly integrate a myriad of features and functions. NEC introduced Flash MCUs with large memory capacities for use with refrigerators, air-conditioners, dishwashers, and magnetic-induction cooking appliances. The 78KOR line of 16-bit MCUs has an inverter control system to achieve high-efficiency motor operation.

“Timer-array units generate three independent pulse-width modulation (PWM) waves and their complements,” Shin explains. “The six PWM signals drive a three-phase inverter power stage connected to a three-phase motor.” This enables the MCUs to measure sensor signals and adjust operation automatically to the most efficient mode. Besides energy efficiency, the integrated inverter control creates a one-chip solution that reduces external component count and cost.

Already looking to the future, NEC says it anticipates more automation and networking applications for consumer and industrial applications, and is working on fast analog-to-digital convertors for future product designs.

To help OEMs ensure their products meet the latest safety regulations, STMicroelectronics (Geneva; www.st.com) is offering a software library for its STM32 Flash MCU family. The self-diagnostic software is approved by the VDE, the German Association for Electrical, Electronic, and Information Technologies, and does away with the need for the entire application being evaluated for safety standards when used with ST’s MCUs, saving precious product development time. The software includes a safe-boot sequence, self-diagnostic modules and nonvolatile memory, and will embed safety-related hardware, including clock circuitry.
Sense of the Future

Besides safety and integration, sensors and MCUs are obviously becoming more advanced for an increasingly advanced appliance market. “The home appliance market should expect additional sensors to be implemented in new designs that make products quieter and energy efficient,” Ballard of Microchip says. “Applications such as user interfaces, motor control, and the sensing of environmental conditions (i.e., temperature, humidity, pressure, and current) are driving designers toward new sensor implementations in many traditional appliances.”

In fact, Aengus Murray of International Rectifier (El Segundo, CA, U.S.; www.irf.com) says integration will continue to change the role sensors and MCUs play to bring appliance products to life. He feels the next area of focus will be design tools, which will help OEMs meet new standards quickly and efficiently, while making new functions, features, and options that have yet to be seen. “Future MCUs will continue to drive down system costs through integration and the support of advanced al-gorithms that simplify mechanical systems,” Murray says. “Design tools will support all aspects of the system design and functionality, not just one part of the process.”


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