In today’s housing market, great kitchens, including appliances, are a major selling point for homes. To this end, sensor technologies are being used to augment appliances to become more innovative and energy efficient. Household appliances are major energy users and sensors are used to help reduce power consumption and thus CO2
From monitoring humidity in dryers to maintaining optimal water levels in washing machines (Figure 1), and from controlling spray pressure in dishwashers to monitoring temperature in ovens for better baking results, sensors are playing a leading role in white-goods design, providing the measurement accuracy required by top-flight appliances makers, who, in turn, are striving to make the lives of their customers easier and our environment better.
Figure 1: Washers and dryers require a host of sensors to function efficiently. (Courtesy of Epcos)
Plainly stated, sensor-driven white goods are now just plain smart. It wasn’t too long ago that the smartest thing to hit our kitchen was an espresso maker — a mini attempt at barista quality — but one that required you to measure, froth, and well, do it all yourself. Now, based on the integration, miniaturization, and advances in sensor technology many appliances perform jobs more efficiently and accurately, and as a result, smart appliances are expected to become a major share of the total appliance market as early as 2015. According to a recent smart appliance report from Navigant’s Energy Practice¹ research, the market will grow to an annual value from $613 million in 2012 to $34.9 billion in 2020.
Now let’s look at some specific examples of sensor-driven appliance innovation.
Staying in touch
Buttons and sliders are giving way to haptic feedback — using the sense of touch in a user interface to provide information to an end user. It used to take approximately eight mechanical components to do what one single touch sensor does now. In addition, mechanical switches wear out. Touch sensors are highly sensitive and feature a wide detection area.
The ON Semiconductor LC717A00AR
(Figure 2) is a high-performance, low-cost capacitance-digital-converter LSI for electrostatic capacitive touch sensor that is especially focused on usability. It has an 8-channel capacitance-sensor input and a built-in logic circuit that detects the state (ON/OFF) of each input and outputs the result.
Figure 2: Block diagram of the ON Semi LC717A00AR.
The calibration function is automatically performed by the built-in logic circuit during power activation or during environmental changes. The LC717A00AR
operates as stand-alone when the recommended switch pattern is applied. It features a serial interface compatible with I²C and SPI bus and parameters can be adjusted using external devices whenever necessary. Outputs of the 8-input capacitance data can be detected and measured as 8-bit data.
A video produced by ON Semiconductor (“Touch Sensor Switch Solution for Small White Goods Applications
”) provides a basic understanding of mechanical switches versus touch switch solutions specifically for small white-goods applications. ON Semi chose an ordinary kitchen blender to use in its demonstration to help show the flexibility of design and the ability to implement a similar solution into a variety of end-market applications.
Miniaturization, low power, and greater usability are all important elements when looking at the sensor technology used in white goods. No matter the application, the three are important. For example, the SM351LT
, part of Honeywell’s Magnetoresistive Nanopower Sensor IC Series (Figure 3), is used in such applications as door- and drawer-position detection and fluid flow in white goods. The sensor ICs are ultra-sensitive devices designed with large air gaps, small magnetic fields, and low-power requirements. These sensor ICs use a very-low average current consumption and a push-pull output, which does not require a pull-up resistor. The sensor ICs operate from a supply voltage as low as 1.65 V, ensuring energy efficiency.
Figure 3: Honeywell magnetoresistive sensor IC block/electrical diagram.
The Nanopower Series is available in two magnetic sensitivities for a variety of applications. The SM351LT
is used in apps requiring ultra-high magnetic sensitivity (7 G typical operate, 11 G maximum operate) and a very-low-current draw (360 nA typical). In comparison, the SM353LT
provides for very-high magnetic sensitivity (14 G typical operate, 20 G maximum operate) and a very-low-current draw (310 nA typical).
A pressure sensor can be used to measure the level of water in the drum of a washing machine. Amphenol’s NPA series of pressure sensors (e.g. the NPA-100B-10WD
) is a combination of Amphenol’s Advanced Sensors’ SenStable silicon-fusion bonded-pressure die technology and packaged electronics (Figure 4). The NPA product series features a miniature size as a cost-effective solution for applications that require calibrated performance. It is available in Gauge, Absolute, or Differential pressure ranges with mV, amplified analog, or digital outputs.
Figure 4: The Amphenol NPA series of pressure sensors is available in gauge, absolute, or differential pressure ranges.
The series provides highly stable, amplified, and calibrated pressure measurements in a cost-effective surface-mount package. These sensors are intended for printed-circuit-board mounting and delivered in tape-and-reel form to simplify manufacturing handling.
According to the White Goods Solutions Guide² published by Texas Instruments, white-goods motors are often oversized to account for the load torque changes and transients, resulting in inefficiency and noisy conditions. As a result, energy efficiency suffered. In comparison, the Guide reports that by using digital signal controllers, designers can achieve smaller, quieter motors with energy efficiency as high as 85 to 90 percent compared with up to 50 percent in the former case.
By using such technology as power-factor correction (PFC) to counteract continuous transients and surge currents inherent in electric motor during, for example, appliance wash cycles, PFC is now performed externally by a dedicated IC or via software on an MCU.
Compliance with the IEC 60730 specification that governs such elements as microcontrollers, detailing new test and diagnostic methods for the real-time embedded software ensures the safe operation of embedded control hardware and software.
Only five years ago, IEC changed the definition of a low-power circuit from 100 W to 15 W. All user-accessible controls must be low-power circuits. Offline 12 V to 24 V power supply lines are typically available in most homes. Buck controllers and linear regulators convert this offline voltage to something the MCU on the thermostat or indoor controller unit can use — i.e. 5 V, 3.3 V or 1.8 V.
When reliability and motor control accuracy are key, isolation products that block high voltage, isolate grounds, and prevent noise currents from entering the local ground are used.
The greatest impact on white goods, especially large appliances, going forward will be the expansion of cloud computing and the smart home. A home-mesh network consists of wirelessly connected appliances that are controlled remotely. The combination of ZigBee-based solutions, radio frequency (RF) ICs, Wi-Fi, near-field communication (NFC), and software supporting each interface is rapidly moving higher numbers of appliances onto the cloud.
For more information about the parts discussed in this article, use the links provided to access product pages on the Hotenda website.
- Navigant Energy Practice
- TI White Goods Solutions Guide