Sensors in Consumer Electronics

By Carolyn Mathas

Contributed By Hearst Electronic Products

Sensors are hardly new elements of consumer electronics design. Recently, however, they have become much smaller, cost less, and are much more power efficient than in the past. These developments have promoted their use in portable devices (the user appeal of smartphones and tablets these days depends to a large extent on the quality of sensor solutions), gaming (sensing the movement of the user allows for that movement to be translated into on-screen game character motion), navigation, and home appliances.

Advances in sensor technology is also making new and exciting applications possible in the fields of home automation, robotics and digital health. However, no more so than in the so-called “wearables” sector, where fitness bands and other peripherals take input from biometric sensors and then use radio connectivity to bring to bear the analytical power of a smartphone or tablet, which in turn can tap the cloud for still more computing and communications resources.

There are now apps that use smartphone sensors to provide touch-free analysis of someone’s heart rate simply by analyzing his or her skin tone; with each heartbeat blood rushes to the face and decreases the amount of light reflected from the skin, which, although not noticeable to the human eye, is measureable by a smartphone sensor.

According to a recently published research report, “Sensor Market in Consumer Electronics” by MarketsandMarkets, a global market research and consulting company based in the U.S., consumer electronics sensor applications will represent a $29.25 billion business by 2020.

Sensors used in consumer electronics and household appliances include pressure, proximity, motion, temperature, flow and level, acoustic, touch, and image sensors. Let’s now look at a few representative devices that can typically be found working in consumer electronics end products.

An example of a pressure sensor used in consumer applications is the LPS331AP MEMS pressure sensor from STMicroelectronics (Figure 1). This ultra-compact absolute-piezoresistive pressure sensor includes a monolithic sensing element and an IC interface able to take the information from the sensing element and provide a digital signal to the external world. The sensor enables 3D indoor positioning and enhanced GPS in portable devices and is used in such applications as indoor and outdoor navigation, enhanced GPS for dead reckoning, sport watches, and altimeter and barometer measurement for portable devices.

The VENSENS process used by STMicroelectronics to manufacture this sensor allows a monosilicon membrane to be produced above an air cavity with a controlled gap and defined pressure. This membrane is extremely small when compared with traditional silicon micro-machined membranes, and is designed to prevent membrane breakage. The sensor is available in a small, plastic land-grid array (HCLGA) package, and operates over an extended temperature range from –40° to +85°C.

STMicroelectronics LPS331A

Figure 1: Block diagram of the STMicroelectronics LPS331A.

Another example of a part commonly used in consumer electronics applications is the Microchip MCP9800/1/2/3 high-accuracy temperature sensor (Figure 2). Employed in entertainment systems, mobile phones, and for general-purpose temperature monitoring, these sensors deliver an accuracy of ±1°C (maximum) from -10° to +85°C.

Microchip MCP9800/02

Figure 2: Block diagram showing a typical application of the Microchip MCP9800/02.

The Microchip sensor features an operating voltage range of 2.7 to 5.5 V, a two-wire I²C/SMBus-compatible serial interface allowing up to eight devices to be controlled in a single serial bus, power-saving one-shot temperature measurement, and is available in SOT-23-5, MSOP-8, and SOIC-8 packaging.

Sensors are now used to remotely monitor home appliances. Selection criteria for these apps begin with high accuracy. One such temperature watchdog is the PCT2075 temperature sensor by NXP Semiconductors (Figure 3). It boasts ±1°C precision over a –25° to +100°C range, where most temperature measurements occur.

NXP’s PCT2075 temperature sensor

Figure 3: NXP’s PCT2075 temperature sensor enables remote monitoring.

The resolution of this device is 11-bits, or +0.125°C, allowing you to sense minute temperature changes while the outstanding accuracy ensures quick response on buses with many I²C slaves, in this case allowing up to 27 devices on the same I²C-bus segment using only three device pins. Typical industry-standard devices only permit eight devices on the same I²C-bus segment without elaborate multiplexing schemes. This feature is particularly beneficial when determining temperature gradients over a surface.

The PCT2075 can be configured for different operation conditions. It can be set in normal mode to periodically monitor the ambient temperature, or in shutdown mode to minimize power consumption. Applications include personal computers, solid-state drives, thermostats, and LCD TVs.

For the portable electronics market, minimizing power consumption to provide longer battery use without charging is a major challenge. LCDs and back lighting are particularly power hungry. By using ambient-light sensors, backlight LEDs can operate longer and with substantial performance improvement. These illumination sensors, or optical sensors, are used in cell phones in particular to deliver automatic control of display backlight brightness over many lighting conditions, from darkness to direct sunlight.

An example of an ambient-light sensor well suited for this task is the TSL2591 from ams, a very-high-sensitivity light-to-digital converter that transforms light intensity into a digital signal output that is capable of direct I²C interface (Figure 4).

ams TSL2591 light-to-digital converter

Figure 4: The highly-sensitive ams TSL2591 light-to-digital converter transforms light intensity into a digital signal output capable of direct I²C interface.

The device approximates human eye response, and combines one broadband photodiode (visible plus infrared) and one infrared-responding photodiode on a single CMOS integrated circuit. Two integrating ADCs convert photodiode currents into a digital output that represents the irradiance measured on each channel.

Digital output can be input to a microprocessor where ambient light level in lux is derived using an empirical formula that approximates the human eye’s response. The TSL2591 supports a traditional-level style interrupt that remains active until firmware clears it.

Motion sensors continue to gain significant ground in consumer applications. Innovations in MEMS technology based on size, cost, and reduced power consumption have moved these motion sensors from their industrial and automotive base to handheld consumer devices. These inertial sensors are being used in laptops, MP3 players, digital cameras, TV remote controls, game controllers, and mobile phones, enabling enhanced operation.

Typical applications include image and video stabilization, counteracting hand jitter. These sensors also are used in drop systems to protect hard drives from damage due to a fall, whether housed in PCs, MP3 players, cameras, mobile phones, or tablets.

The MPU-3000/MPU-3050 motion-processing unit from InvenSense (Figure 5) supports 3D motion processing and gesture-recognition algorithms. The MPU-30X0 family significantly extends and transforms motion-sensing features provided by accelerometers beyond portrait and landscape orientation. When used together with a digital three-axis third-party accelerometer, the MPU-30X0 collects data via a dedicated interface, while synchronizing data sampling at a user-defined rate.

InvenSense MPU-3000/MPU-3050

Figure 5: Block diagram of the InvenSense MPU-3000/MPU-3050.

The total data set obtained by the MPU-30X0 includes three-axis gyroscope and accelerometer data, temperature data, and the one-bit external sync signal connected to the FSYNC pin. The external sync signal connected to the FSYNC pin supports image, video, and GPS synchronization. The device is factory calibrated and shock tolerant.

MPU-30X0 not only provides accurate 1:1 motion tracking for some of the more common consumer electronics applications such as still/video image stabilization, gaming and dead reckoning, the 32-bit part can be programmed to deliver an advanced user interface for multiple kinds of gesture and character recognition applications.

Intelligence, reliability, low power, low cost, and high integration continue to be the impetus behind sensor use in consumer electronics. As people continue to insist on the ability to manage the world in front of them, on them, or even in their homes from afar, there will continue to be a high level of growth in sensor use, and that demand in turn will drive advances in sensor technology.

For more information on the sensors discussed in this article, use the links provided to access product information pages on the Digi-Key website.

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