It is the beginning of a new year, and CES 2014 might have begun by the time you are reading this article. One common theme that we can expect in a lot of products launched at CES this year would be the dependence on a multitude of sensors. These sensors are important for all the smart functionalities you see in high-end smartphones. Join us in this story as we check out the cutting-edge sensor technologies, and how you can implement them in your next electronic design.
Products released last year, and the Internet of Things itself, have acknowledged many sensor-based technologies. Some such technologies with the types of sensors used are discussed below. Anup Tapadia, founder, TouchMagix says, “The types of sensors that are emerging and have become more famous are the time-of-flight-based sensors that use reflected light pulses to measure the distance. These types of sensors have made 3D sensing technology famous.”
9-axis sensor fusion technology. This technology works with gyroscopes, accelerometers and magnetic sensors from any manufacturer without any restriction and thus allows us the required flexibility and control. Ideally, the precision of sensor fusion technology is very difficult and can delay the launch of a product as it includes so many steps, such as sensor integration, enhancement of signal, sensor drift, calibration, power consumption and magnetic drift. This technology uses low-power fusion co-processor with 9-axis sensor fusion algorithm that fuses and continuously auto-calibrates the sensors using a small fraction (less than 1 per cent) of the power of even a low-power microcontroller sensor hub.
Fig. 1: Comparison of four accelerometer
modules launched in the previous year
Fig. 2: Comparison of four motion
SpacePoint technology. It is also a 9-axis sensor technology in which 3-axis geomagnetic sensor is integrated with 3-axis accelerometer and 3-axis gyroscope, which is then fused with the 9-axis sensor fusion algorithm to get accurate motion sensing for consumer applications (like controllers for TV, set-top boxes, video games, etc). It provides a very accurate performance with high resolution, effective responsiveness and 1:1 motion tracking. Imagine playing a video game and controlling the characters in the game just by your body actions with 360-degree pointing accuracy, even without touching the screen of the video game or any controller and, most importantly, without any time lag. This beautiful application has become possible due to SpacePoint technology.
Fig. 3: Comparison of four
optical sensor development
Electro-mechanical polymer (EMP) actuator technology. EMP is a flexible, light and ultra-thin film with electro-active properties. It uses a piezoelectric polymer material which elongates on application of an electric field. This material is used to generate very fine and powerful sensors and actuators to enhance the sensory user experience in electronic devices. EMP, which is only about 200µ thick, stretches and elongates on application of a charge that creates vibration on the surface and causes sounds and surface deformation. The EMP touch sensors are considered perfect for the precise gesture-control applications such as squeezing detection and pressure. The sensors manufactured by this technology are ultra thin (<200µ), as light as a feather—weighing lesser than 0.001 gm and have a fast response time (<5 milliseconds).
Table I indicates different sensor-based technologies that have helped the launch of some amazing consumer electronics products in the previous year.
Tools and solutions available for design engineers
The continuously-evolving sensor world has become so important that lots of initiatives are being taken in this field. Every now and then we see many conferences, expos and seminars to promote the knowledge of sensor-based technologies and products. The worldwide market for sensors also includes kits, modules and training programmes to help the young engineers take initiatives and innovate new products.
There are quite a few development boards available in the market for a geek who wants to try out a few sensors and build some interesting applications. Harsha Bagur V., group manager, In-vehicle Infotainment, Robert Bosch, shares some valuable information on this. “Popular development boards like Arduino, Raspberry Pi and BeagleBone are being increasingly used by DIY enthusiasts. Arduino, however, is suited for simpler and less process-intensive and interactive applications. Both Raspberry and BeagleBone come with popular OS distributions like Linux and Android. BeagleBone, especially, does have multiple options for external connectivity and hence there are possibilities to realise use cases with multiple external sensor connectivity.”
Priya Kuber, managing director at Arduino India, reminds us that all programming boards these days have advanced software libraries to detect sensors. A sensor usually sends a string of data, and how to interpret the data into a digital form and make use of those values to get desired result with a programming board is the job of a design engineer these days. “Since everything is based on data, I would say that the new ‘tools and initiatives’ are the software libraries that run on the board. For example, Capacitive Sensing Library is a library that converts ordinary aluminium foil into a useful calibrated sensor,” she adds.
Availability of standalone sensor evaluation boards as commercial off-the-shelf units have immensely helped design engineers integrate the same in their designs at prototyping/proof-of-concept stage and design products with use cases that were never thought of earlier. “One of the biggest gainers of such sensors is wearable computing category—smart watch, wrist bands for health and wellness, sports performance monitoring, etc. And, sensor providers publish APIs/trainings that enable designers adapt to a particular sensor quickly,” says Dhaval Vasa, project manager at eInfoChips.
Some sensor-based kits and modules available with their price list are listed in Table II.
Apart from these modules, there are some development tools of popular brands, based on some particular types of sensors, that can act as a learning source for the young engineers and also help them in various innovations.
How to select a sensor for your application
A sensor should be selected depending on the application in mind. Sensors are of two types: limit detector and qualitative and quantitative analysis measuring element. “Limit detection type of sensor gives out logic 1 or 0. This operates as a watchdog in the system and annunciates in fast response at occurrence of monitored parameter. Specifically, this could be an active element used for a particular purpose as a feedback circuit in a power supply, or a Hall effect switch detecting the presence of magnetic field of rated magnetic flux and direction. The other example is a PIR detector detecting presence of an object and movement of the same. Qualitative and quantitative analysis type of sensor could do the job rather slowly and deliver its response in a required electrical form,” explains P. Chow Reddy, R&D manager, Power Division, ICOMM Tele Ltd.
There are certain things which a designer has to ensure so that his product does not fail due to a faulty selection of the sensor involved.
Identifying the sensing parameter. The parameter could be in any form such as voltage, current, frequency, temperature, pressure, light, touch, presence, sound and chemical reaction to name a few. Any of these needs to be converted to electrical form for electronic analysis. “A thermistor varies its resistance depending on the thermal stress over it. Thermistor as an element in a potential divider circuit results out a temperature corresponding to the potential across it. An engineer working on this needs to analyse the range of operation of thermistor, way to get safe operating range of the sensor, observe the performance of the thermistor to see what time it takes to convert the parameter, and the linearity and response of the sensor for the physical changes occurring across it,” explains Chow Reddy.
Dhaval Vasa gives us advice on the considerations to be made whilst selecting an IR sensor for sensing the proximity of objects. “If you take an example of a proximity sensor (IR-based), which emits an electromagnetic field or a beam of electromagnetic radiation, and looks for changes in the field or return signal, one essentially needs to carefully consider the ‘sensing frequency’ at which sensing data is provided, ‘range’ that gets covered in form of angle/distance with ‘resolution’, ‘size’ depending on the device on which such a proximity sensor will be mounted, and operating environment/conditions under which such a sensor will function.” Such a sensor can have high reliability and long functional life due to absence of mechanical parts and lack of physical contact between the sensor and the object.
Reliability. Ensuring a robust design with maintenance-free packaging is very important. This is because sensors are that part of the device which mostly comes into contact with the world, and hence has to have the ability to withstand harsh environment without losing on performance. Sahil Khan, embedded systems consultant at Upheave Systems Pvt Ltd, adds that, “We have seen soil moisture sensors losing accuracy in saline agricultural soils. With huge requirements for the IoT, maintenance is a big no-no for a sensing node.” A sensor must be able to transduce information reliably over and over again, and that too within reasonable accuracy.
Easy integration. For the developer’s perspective, using ADC, employing filtering equations, extracting data and then calibrating the firmware is troublesome. This is why, to reduce design effort, pre-calibrated sensors which support common interfaces like TWI/I2C or SWI, SPI, etc are preferable.
A common example is the use of NTC or PTC thermistors versus a DHT11 sensor to read temperature and humidity data. “DHT11 temperature and humidity sensor features a temperature and humidity sensor complex with a calibrated digital signal output. By using the exclusive digital signal acquisition technique and temperature and humidity sensing technology, it ensures high reliability and excellent long-term stability. This sensor includes a resistive-type humidity measurement component and an NTC temperature measurement component, and connects to a high-performance 8-bit microcontroller, offering excellent quality, fast response, anti-interference ability and cost-effectiveness,” explains Sahil.
He adds another example, the SP1202S01RB sensor by National Semiconductor, which is used for measuring liquid level utilising a pressure sensor. Most importantly, this sensor is being used for sensing the quantity of water in drought-affected areas.
Software. There are also some sensors whose role mainly depends on the software. These analyse the environment by sensing some parameters and make use of a software to come to a decision. Fuzzy logic plays a vital role in such sensors. Chow Reddy explains, “Another case where sensor plays a small role but circuitry and software play a vital role is load cell for weighing applications. The load cell here is a wheatstone bridge to develop a differential potential at the stress applied on one of the wings of the bridge. The developed potential puts in few microvolts prone to get affected by noise due to external disturbances, vary due to vibrations created over the platform. ADC employed to read these parameters need to be properly selected.” Chow Reddy further explains that software to reject the noise as well as average the weight data to produce a calibrated weight accurately is as important as a physical sensor.
New sensors that design houses are looking forward to
Several sensors have emerged in the Indian market since last one year for different applications. The most awaited in power electronics and industrial applications, according to Reddy, is Allegro’s ACS712—a linear current sensor in a SOIC 8-pin package. He explains that it brings in economical and precise solutions for AC or DC current sensing for applications including motor control, load detection and management, switched-mode power supplies and overcurrent fault protection. “The device consists of a precise linear Hall sensor with a copper conduction path located close to each other. Applied current flowing through this copper conduction path generates a magnetic field, which is sensed by the integrated Hall IC to develop a linear potential at its output. Device accuracy depends on close proximity of the magnetic signal to the Hall transducer,” he adds.
Interesting developments. The year 2013 saw many brands enter the field of sensors along with the older brands that brought some amazing innovations in this field.
1. ARM has come up with ‘Sensor Bubble’ that is supposed to surround car drivers in order to keep them safe whilst driving. It allows the driver to slow down safely in case of a tire burst (for example) and would send an RFID signal to the traffic following to alert the other drivers to slow down too; the signal would also go into the drivers’ GPS to suggest them an alternate route.
2. Open Geospatial Consortium (OGC) came up with ‘The Sensor Web Enablement Initiative.’ As per this initiative, the web service is interfaced with data coding in order to create building blocks for a worldwide sensor web that would create a framework of open standards and allow diverse web-connected sensors. This would also provide sensor systems that can be accessed in an independent, interoperable platform and would provide a uniform way for use in remote sensing, disaster management, public safety, environment monitoring and many other different applications.
3. SENSUSS came up with S3, which is a wireless helmet-mounted impact logger for car and bike racing drivers. It transmits data to the Eurotech Everyware Cloud so that it can be used to provide instant information on the level of the impact that an athlete experiences, in case of a crash, to the coaches, parents and even to the doctors.
4. Raytheon’s Space and Airborne Systems that builds radars and other sensors for aircraft, ships and spacecraft is in a contract with ISRO to modernise the Indian air navigation system.
5. Autonics India has come up with CNE series sensor connectors that increase productivity by decreasing workforce and work time by 50 per cent.
Select with care
Sensor selection is very important for a design engineer, and we hope this article would help you select the right one. Priya, explains, “Most products that are user based are supposed to be started with the end-effector in mind. However, real-life situations are supposed to be considered whilst picking a sensor.” Priya goes on to share a recent problem which her team went on to solve, “A recent project had us using a simple IR to control lights for a dance choreography piece, but at the last minute it startedmisbehaving at the big stage. That gave us a very important wireless design lesson—always have a hard switch too installed in the product just in case wireless fails. We did save the day by re-doing the circuit that night!”
Sneha Ambastha is a technical journalist at EFY Gurgaon, while Dilin Anand is senior technical correspondent at EFY Bengaluru