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issue: May 2005 APPLIANCE Magazine

Sensors and MCUs
Controlling the Future of Appliances


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by David Simpson, Contributing Editor

Microcontroller and related component prices continue to decline while sensor selection expands, providing appliance producers with cost-effective opportunities to upgrade and differentiate their products.

SmartFan Inversion is a fan speed control that combines an a.c. to d.c. power supply and d.c. fan control/alarm to provide the best of both worlds. The device, from Control Resources, Inc. (Littleton, MA, U.S.), is said to offer benefits such as acoustical noise reduction, temperature regulation, greater product reliability, and improved safety and energy savings.

Integrating Functions

As appliance companies ramp up the rate at which they make product changes, microcontrollers and sensors are playing a huge role. Their use can add precision, improve motor efficiency, or permit new, user-friendly functions. For instance, late last year Magnetek, Inc. (Los Angeles, CA, U.S.) announced an agreement to supply Electrolux in North America with Smart Appliance Modules for front-loading washers. The modules are microcontroller-based power controls that contribute to front loaders’ enhanced performance by increasing motor efficiency and load-balancing ability. At the same time, they reduce acoustic noise and electromagnetic interference, among other attributes.

Stephen Caldwell, director of the Home Appliance Solutions Group at Microchip Technology Inc. (Chandler, AZ, U.S.), adds that sensors and controls can offer more than just practical benefits. “The cost of solid-state electronics continues to decrease every year. Thus, the budget for the control board bill of materials can afford to include microcontrollers with higher memories and higher pin counts. This, in turn, enables appliances to have more features, which end customers will perceive as value added,” he tells APPLIANCE. “The higher pin count microcontrollers will be used to drive more and more LEDs, relays, and interpret keypads, switches, and sensors. These newer systems will provide a better user experience for the consumer.”

As electronics capabilities improve and costs decline, it is becoming more feasible to combine multiple functions. As an example, Tom Ricono, vice president of Business Development at Diehl Controls North America (Naperville, IL, U.S.), points to laundry appliances. “With the horizontal platform, we are able to integrate electronics in both machine and motor control to greatly improve efficiencies, clean-ability, and perform many product enhancements,” he says. “Advancements and price reductions for semiconductors allow appliances to be smarter, use more sensors in real-time, and offer more control to the user. Faster microprocessors allow real-time embedded systems to perform instantaneously.”

Mr. Ricono says that one example is controlling motor speeds to re-balance spin loads as the imbalance happens and before it becomes a nuisance to the user. Almost unlimited code space allows multiple languages, friendly one-touch starts, and icons that mimic computers. “With increased inputs and outputs, large code routines, and multiple calculations, being able to run at real time and react instantaneously gives the appliance better performance and can save energy,” he explains.

With product life cycles being reduced every decade, the development cycle must also be reduced while software size and complexity is increasing, Mr. Ricono adds.

“In the 1980s, average code size was 1 to 4K, then in the 90s it was 8 to 32K. Now programs are exceeding 128K, and full alphanumeric displays are common,” Mr. Ricono notes. “One issue is verification time. Probably every eight lines of code is a decision, so with 128K of code, there are thousands of decisions. Does increasing code sizes and, therefore, complexity mean more test time? Nobody wants to have the software mess of Microsoft, with patches and errors and hidden bugs surfacing after release.”

To address this issue, Diehl Controls uses an Object Oriented Process that is said to greatly reduce software development time, reduce verification time, check all decision paths, and improve reliability. “This allows us to deliver error free code and reduce the approval stage without putting our customers at risk,” Mr. Ricono says.

Control technologies have changed tremendously in philosophy and implementation since moving into appliance applications, adds to Arefeen Mohammed, system applications at Texas Instruments (Houston, TX, U.S.) TMS320C2000 Group.

“Most systems in 1994 used universal motors and simple on/off controls. Today, many have moved to three-phase induction, brushless d.c. motors with advanced algorithms for higher performance and power factor correction (PFC) to meet regulations,” he tells APPLIANCE. “With the advancement in controllers, the PFC can now be integrated into the motor controller, eliminating the additional PFC controller required previously. For the manufacturer, that has reduced total board size, chip count, and provided high performance at reduced cost.”

At the same time, Mr. Mohammed says that appliance customers prefer a two-layer board for reduced cost. This means that the appliance designers have to better manage noise. “There are things we do to ease their task, like include input qualifiers and design our analog and digital buses to make them much more immune to noise. Also, by leveraging smarter, mathematical algorithms, we can reduce the size of any EMI (electromagnetic interference) filters, and still meet regulatory demands. This can be a significant cost savings,” he explains.

Another issue is that as engineers add sophisticated software to gain performance and reduce cost, appliance customers often get more concerned with protecting their work. “The risk is that an unauthorized access can compromise proprietary techniques,” Mr. Mohammed says. “Here again, we help designers protect their intellectual property by building security features into our chips. These ensure that the contents are secure once they are password protected in the memory space of our devices.”

Another trend has been the move toward more sophisticated electronic controls. In the 1990s, OEMs began to increase features and complexity with the use of 4-bit MCUs. By the mid- to late-90s, appliance companies began to look to 8-bit controllers to handle more complexity. Some appliance makers chose to use low-cost 16-bit controllers to save money by providing extensive peripheral functions, which can eliminate the need for external devices and facilitate the system integration process without cost penalty.

Renesas Technology America, Inc. (San Jose, CA, U.S.) added a 16-bit controller to its product line in 1999. As the company has reduced the sizes of its chips, it has had to address electromagnetic compatibility (EMI and EMS), which increases with the smaller geometry process. But as Ritesh Tyagi, senior product marketing manager of Renesas’ System LSI Business Group, points out, “This problem can be handled at the chip level as well as at the system level. Renesas incorporated many EMI/EMS countermeasures inside the chip. For example, we implemented special noise filters across critical pins, arranged all peripherals’ input signals to be channeled through protection circuits, and enhanced tolerance for static and latch up, besides using other methods.”

This customized regulator for SR motors comes from Matsushita Electronic Components (Europe) GmbH (Lüneburg, Germany). The entire control is based on an 8-bit microcontroller that provides comprehensive functions at comparatively low manufacturing costs.

“Zensing” a Connection

Sensor technology is also bringing appliance makers performance benefits. Sensors for glass ceramic cooktops, for example, need to work in an extremely high-temperature environment—in some cases up to 800ºC, reports Kim Lezatte, vice president of Sales at Ceramaspeed Inc. (Maryville, TN, U.S.). “We’ve been using a single primary high limit switch to assure that temperature limits are not exceeded. But these have a fairly wide tolerance—about 25ºC to 30ºC. Because of the tolerance, we can’t take the maximum temperature quite as high as we would if we used a sensor with a narrower tolerance. In addition, the control turns the heating cycle on and off to assure it doesn’t overshoot the maximum top glass temperature of around 560ºC. This slows the amount of time it takes for water to boil on the glass ceramic surface.”

By switching to a more accurate high temperature sensor and changing how the control operates, Ceramaspeed says it has reduced boil times by as much as 19 percent. The new platinum sensor has a tolerance of just 7ºC, allowing higher set points. The EPIC control, from DDS Electtronica of Modeno, Italy, actually aims to take the temperature higher than 600ºC for up to
7 min for more rapid boiling. After that, the temperature automatically drops to between 590ºC to 600ºC. Due to the risk of the high heat damaging the surrounding cabinets, after another 20 min, the temperature will again drop, this time to about 560ºC.

The controls also aim to bring down temperature to low settings more rapidly with the assistance of the sensor feedback. To reach the desired temperature, the control keeps power off rather than cycling on and off as previously done. Temperatures have been known to drop as much as five times faster with this approach.

Another feature with this closed-loop system is the ability to control the “keep-warm” set point. The sensor provides feedback to the control, allowing the output to be adjusted. This keeps the glass temperature, and more importantly, the food inside the pan, at a constant temperature without scorching.

Interconnecting appliances and other household products has long been practical, with signals carried through specialized cables, phone lines, power lines, or wirelessly. Wireless technology would seem to be a promising approach, since it dispenses with potentially expensive dedicated hard wiring and avoids compromises in performance caused by dual-purpose wiring.

Wireless technology, used in products like cordless phones and television and audio remote controls, is growing. Wi-Fi and Bluetooth technologies are also playing a growing role in today’s computers and peripherals, cell phones, and audio/video equipment. However, many manufacturers are hesitant to jump on the bandwagon. Even if they think users might be interested in a networked wireless feature, many OEMs have been concerned about expense, reliability, complexity, eventual obsolescence, and a lack of widely acceptable standards. The good news is that chip and sensor and control suppliers are making efforts to come up with wireless solutions that are relatively low cost, reliable, widely accepted, and will communicate even between different manufacturers’ products. One emerging development is the Institute of Electrical and Electronics Engineers (IEEE) 802.15.4 ZigBee standard.

“Some wireless solutions in the home, such as cell phones and WiFi, offer high bandwidth, which allows them to push through a lot of data, including voice and video,” explains Mr. Caldwell of Microchip. “But because of the high bandwidth, there is a lot of overhead, and the expense is higher. Other technology, such as Bluetooth, offers less bandwidth and somewhat lower expense. But for many applications, you really don’t need even that much bandwidth. If you are simply turning things on and off or setting temperatures, for instance, your technology doesn’t need voice or video capabilities. It is in these simpler command and control applications that the IEEE 802.15.4 ZigBee standard can shine.”

To promote and technically advance the standard, several companies have joined to form the ZigBee Alliance. More than 100 members participate, including Microchip, Freescale Semiconductors, Mitsubishi Electric Corporation, Philips Semiconductors, Honeywell, and Samsung Electronics Company Ltd. Last December, the group ratified the first ZigBee specification after 2 years of worldwide development and interoperability testing. For those members that have already announced ZigBee-ready technology, the ratification of the specification and the expected publication in April 2005 (as of press time) enables them to quickly enhance their products and begin testing to obtain ZigBee-compliant certification.

One of the key advantages of ZigBee, says Mr. Caldwell, is the interoperability. “If one vendor has the technology, its products will be able to talk to another vendor’s,” he points out. “ZigBee networking can support many topographies, such as star or mesh, and can be used to connect thousands of objects—certainly more than are likely to be needed within a house. Another advantage is low-power operation, which can result in battery life measured in years.”

Microchip already has ZigBee-ready technology and offers free software stacks that permit its PIC microcontrollers to work in tandem with any 2.4 GHz RF signal transceiver to form a ZigBee network. For product development, the company supplies the PICDEM Z kit with the hardware, software, source-code, and PCB layout files to enable the developer to generate a small working system. “These kit components can be put into consumer goods to see how they work,” says Mr. Caldwell. “They can accelerate time to market.”

Brett Black, commercial wireless operations manager at Freescale Semiconductor, Radio Products Division (Tempe, AZ, U.S.), is seeing a push from customers toward standards-based solutions. “In the last decade I’ve never seen a product that has such customer pull and interest. There are few customers who haven’t heard of ZigBee or aren’t interested in wireless connectivity in their markets,” he tells APPLIANCE.

“Industrial and building automation are areas where much of the initial activity will be,” Mr. Black continues. “In building automation, for instance, controls can integrate and centralize management of lighting, heating, cooling, and security, while in an industrial setting ZigBee could reliably extend existing manufacturing and process control systems. We anticipate that wide adoption of home applications will take off based on meeting price targets, which will become more likely as the technology spreads.”

Mr. Black adds that Freescale will offer fully compliant ZigBee chips once specifications are published. “And, as you see more compliant platforms in the market, you will see more customers adopt the standard,” he says. “Another inducement is that the cost of licensing a ZigBee compliant solution could be as little as U.S. $3,500.”

Selco/ECC (Anaheim, CA, U.S.) suggests that appliance manufacturers can cost-effectively provide improved temperature precision by replacing traditional bulb and capillary temperature thermostats with electronic temperature sensing and control. Typical applications include cooking equipment, refrigerated and frozen food storage, chillers, and HVAC equipment. Available in three configurations, the controllers provide a differential of +2ºF (-16.7°C) high accuracy thermistor temperature sensing of 2ºF, and a set point adjustment of 1ºF (-17.2°C) resolution, set by a potentiometer.

Riding the Z-Wave

While ZigBee offers promise, it is not the only technology in town. Z-Wave was developed by Zensys Inc. (Copenhagen, Denmark), which initially included the technology in temperature and light controls that it produced. In 2001, the company decided to drop the controls and focus on its core technology. It began shipping its own chip and software stack to other home products companies to implement.

“At this stage, we have some 125 companies that have enabled the technology in such products as light dimmers and switches, remote controls, thermostats, motion sensors, security systems, and garage doors,” says Raoul Wijgergangs, vice president of Business Development at Zensys. “There are currently about 50 products on the market, and we anticipate 250 will be shipped by the end of the year.” Among companies in the Z-Wave Alliance, which promotes the technology, are Leviton, Wayne Dalton, Danfoss, and Intermatic.

The ZW0102 Z-Wave single chip is a mixed signal chip integrating RF transceiver, Z-Wave protocol storage and handling, and OEM product application storage and handling in one chip. An on-chip 8-bit MCU handles both the OEM application as well as the wireless communication protocol. Free on-chip flash memory gives the OEM the opportunity to download and run most control applications directly on the chip. This eliminates the need for an additional microcontroller and external flash memory for application code storage.

As with ZigBee, interoperability is seen as a key advantage. For instance, when a garage door is opened, it can send a signal to turn on a light in the house, even if the light control was produced by another company. Alternatively, an action can be triggered over the Internet. The technology uses a mesh network. Each system is said to be very reliable, with each node capable of acting as a repeater to forward messages to the targeted node in the network, and relaying back confirmation that the message was received. Long battery life is another feature.

One proponent of Z-Wave is Intermatic Corporation (Spring Grove, IL, U.S.). It currently has six lighting controls and hand-held remotes using the technology. “Our goal is to have 60 SKUs in the next 12 to 18 months,” says Jeff Bovee, marketing manager for home controls. “These will include moisture sensors, door/window sensors, motion sensors, temperature sensors, and others for both the industrial and retail markets.” According to Mr. Bovee, Intermatic chose Z-Wave because it is reliable and is available at a fairly low implementation cost for a lot of applications.

The ZCPR Series of potential relays is a recent entry in a line of products for the HVAC/R industry. Manufactured by Zettler Controls, Inc. (Aliso Viejo, CA, U.S.), the relays are used to assist in the initial function of single-phase motors that employ start capacitors for high torque. The coil of a potential relay is energized by the potential of the start winding. When this voltage increases to the pick up value, the contacts will open and disconnect the start capacitor. The relay will remain energized until the start winding voltage is removed, or when it decreases below the dropout value.

Getting the Lead Out

Many electrical component suppliers are affected by RoHS, technically the 2002/95/EC Directive of the European Parliament and Council. RoHS stands for Restriction of the use of certain Hazardous Substances in electrical and electronic equipment. The aim of the directive is to ban heavy metals (such as lead, mercury, cadmium, and hexavalent chromium) and two brominated compounds (PBB and PBDE). The directive will be applicable throughout the European Union by July 1, 2006.

Appliance suppliers have been working to comply, where applicable. Martin Leslie, market manager of Therm-O-Disc (Mansfield, OH, U.S.), points out that the latest proposed RoHS standards allow the use of cadmium in his company’s contacts. “As a result, the RoHS initiative has little effect on our products,” he says.

ST Microelectronics (Tours, France) reports that in 2000, it launched a strategic program named ECOPACK to develop and implement solutions leading to environment-friendly packaging and to progressively ban lead and other heavy metals from its semiconductor manufacturing lines. The company has selected three technologies to match the different technical and quality requirements and cover the full spectrum of packages.

NiPdAu technology is well known on the market and is sometimes referred to as PPF (Pre-Plated Frame). The technology is the preferred choice when feasible. Besides the change of a lead frame, a change in materials (glue and molding compound) may occur to meet the higher solder temperature constraints required for lead-free solder.

Pure tin (Sn) is also a common lead-free solution used by semiconductor manufacturers. There are two sub-processes: dipping and post-plating (matt Sn). This technology is selected for all other lead frame-based packages, which are not eligible for NiPdAu.

A third technology, SnAgCu ball, is the material chosen for the balls of all “Ball Grid Arrays” and balls and bumps of Flip-Chips (currently using PbSn). Its melting point is 217ºC, and its composition close to that of one of the most common solder pastes. It is reportedly the preferred alloy selected by the large majority of semiconductor companies and subcontractors.

Based on its SDX Series sensors, the ASDX and ASDX DO Series pressure sensors from Honeywell Sensing and Control (Freeport, IL, U.S.) are designed for applications that require precision pressure management. Typical applications include medical equipment, HVAC controls, and pneumatic controls. The sensors are fully calibrated and temperature compensated with on-board Application Specific Integrated Circuitry (ASIC).

The Next Generation

Another area that continues to develop is capacitive sensor technology. Quantum Research Group (Southampton, UK) earlier this year introduced the QWheel Rotary touch chip, which has a proximity feature that detects a hand moving near the sense field even 50 mm away from the panel surface. This can be used to “wake up” the product and can work in a very low power mode while still sensing hand proximity.

“Menus and options are available now on a huge variety of electrical equipment from washing machines to telephones, and one of the most important factors associated with this is the ease of use, manipulation, and input,” offers George East, product line manager for Quantum’s Exotic Products Division. “Hence, the popularity of this rotary input device. The rotary allows the user to trace their fingers around a ring that will then scroll up and down through their menu. A further advantage of this product is the ability to have a separate proximity detect function which enables the sensor to recognize a hand approaching.”

As well as being a scrolling device for a menu driven piece of equipment, Mr. East says the technology can also take the place of a traditional potentiometer, with the added advantages of not requiring a hole in the panel for a post and then a separate encoder board to take the signals from the pot. “It is for these reasons that we have had inquiries for appliance producers to replace traditional knobs and dials that have always been bulky, unsightly, and difficult to clean around,” he tells APPLIANCE. “If a visual feedback is desired, then this unit can be used in conjunction with optically clear materials, which will allow the user to backlight the rotor through the panel. So, for certain applications, LEDs can light the panel to show where the user is scrolling through the dial. For a smooth, cool-looking dial that is part of the panel, this is the only way to implement such a solution.”

EtherTouch (Cranford, NJ, U.S.) is in the process of introducing an advanced e-sensing chip technology, which it sees leading to the next generation of interactivity between humans and machines. With a wave of the finger, the company’s three-dimensional (3-D) Application Specific Integrated Circuit (ASIC) could replace the computer mouse, touchpad, touch screen, cell phone keypad, or other traditional input devices. It says it has refined capacitive sensing to track the movement of any object, particularly the human body, or material at significant distances with unsurpassed accuracy.

With this new chip technology, a desktop computer display, for example, will track a user’s finger or hand as it passes through the sensing field from several inches away to several feet. The sensors convert the 3-D position (on the X, Y, and Z axes) into a digital signal. A processor chip of any computer or electronic device then interprets the coordinates and direction and translates them into displayed cursor movements and object selection. “It will finally bring true 3-D play to computer games as it can precisely measure combined motion, velocity, and proximity, making a soccer ball kick or a left hook seem more realistic than ever before,” explains David Leis, EtherTouch vice president of Marketing.

“Our chip technology is extremely compelling to designers and manufacturers of mobile display applications, in particular, since the EtherTouch AD7103 requires one, rather than two layers of conductive materials for the screen (e.g., Indium Tin Oxide or Carbon Nanotubes) and a significantly thinner layer on the order of 1,000 ?/sq, which dramatically reduces power consumption and significantly enhances battery life,” Mr. Leis explains. Reducing power consumption, he adds, is highly desirable for both manufacturers and consumers.

“We are seeing a lot of capacitive sensors coming into medical and other areas,” says Leo McHugh, product marketing manager at Analog Devices, Inc. (Wilmington, MA, U.S.). “Despite recognizing the benefit of capacitive sensors, designers traditionally have had to implement a special purpose capacitance-to-voltage front end that adds to circuit complexity and overall design time. The introduction of our single chip capacitive-to-digital converter will simplify this design task and provide a higher accurate output.”

The company’s new family of 24-bit sigma delta capacitance-to-digital converters (CDCs) are said to ease sensor and instrumentation design and eliminate the constraints of traditional capacitance sensor signal processing solutions by enabling higher accuracy and complete analog functionality on chip.

Mr. Ricono of Diehl points out the importance of integrating sensors into a system to allow it to measure performance. “A weight sensor, integrated in the damper, is one of the new sensor applications in washing machines. This improvement gives our customers unique advantages. They, in turn, can command a higher selling price and the market is accepting performance over low cost. Everyone wants the best performance without requiring additional effort,” Mr. Ricono says.

MEMS flow sensors are a newer product for Omron Electronic Components LLC (Schaumburg, IL, U.S.). “One HVAC application is to use them to detect a clogged filter,” points out Steve Massie, manager, Advanced Technology Group. “They are more common in commercial than in residential applications, where a less expensive pressure switch is sometimes used. For us, the main markets are in such health and medical applications as respiratory ventilators and anesthesia units, as well as in commercial HVAC and energy management.”

It is clear that today’s popular premium appliances require sophisticated sensors to achieve the enhanced performance expected. “The user of a high-end appliance demands a quiet, energy-efficient machine that delivers uncompromising results. The sensors and microcontrollers needed to achieve flexibility, high accuracy, or low power have different requirements and need different technologies,” notes Mr. Caldwell of Microchip. “But, as time progresses, the technology utilized for high-end appliances will be optimized for cost and used in standard appliances. Thus, the technology that can be mass produced at a reasonable cost will prevail.”

 

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