Category Archives: Sensors

Wireless sensors sans batteries

The Internet of Things has led to several simple sensors being used for applications requiring reporting of their readings wirelessly to a gateway or hub. However, most sensors require to be powered from batteries, creating logistical and cost barriers to several use cases. Now, many wireless sensor modules appearing on the market do not require batteries, as they are ultra-low power types.

Several key building blocks are necessary to make up a wireless sensor module meant for IoT use. The first among these is the sensor itself, its signal feeding a micro-controller that processes and packages it for transmission. The final part consists of a radio transceiver to send the information to its destination. Even with the most careful logic design, these building blocks work at a minimum of 1.8V, using up several tens of microamperes at modes requiring the lowest power.

However, in the last decade, extensive research has resulted in development of sub-threshold circuits involving logic, memory and RF. Transistor switching, in conventional logic design, takes place between saturation and an on-off state, dominated by leakage currents. Switching mostly occurs at a gate-to-source voltage or VGS of about 0.5V, which is the threshold voltage or VT for the transistor. In conventional logic, VGS < VT, is the condition for the transistor to remain in the off state. Sub-threshold circuits use this off-state region for the two operational states of a transistor. With the transistor's gate voltage operating below the threshold, the supply voltage can go lower than the conventional 1.8V. An active logic circuit consumes power relative to the square of the supply voltage. Therefore, operating at lower supply voltages can mean considerable power savings. The drawback in this manner of operation is that switching speeds slow down – but that does not hamper many applications. Another requirement of sub-threshold circuits is that a careful control is to be exercised on device physics, including circuit structures. These are necessary to mitigate the effects of temperature variation and noise. However, researchers have provided answers for these problems as well and the solutions have proven themselves practically. Functioning circuits are available for analog, microprocessors and memory devices. Sub-threshold designs are now starting to appear in the market as full SOCs. Universities of Michigan, Virginia and Washington have culminated their research efforts as a two-year old startup, PsiKick. They are preparing a sub-threshold circuitry based wireless sensor module that will operate without batteries. Aside from the RF transceiver, a micro-controller and a sensor front-end, the module will include blocks for energy harvesting. This makes it a self-powered sensor platform that can be used in a wide array of applications. Another design, a second-generation version, is on the cards. This is based on standard CMOS technology and a demonstrable product is due any time soon. The sub-threshold module requires astonishingly small power to operate. Compared to sensor platforms currently available, these modules will consume 100 to 1000 times less power. When fully operating, the micro-controller consumes only 400nW while the RF transmitter generated 10µW, which is effective within a 10m range. The module operates within a supply voltage range of 0.25 to 1.2V. That makes the module eminently suitable to the output capabilities of most energy harvesting methods.

How Are Sensor Hubs Helping Android?

The duties of a sensor hub are rather specific. They usually take the form of an additional micro-controller unit, a coprocessor or a DSP that integrates data from various sensors and processes them for the benefit of the main central processor. Not only does this technology off-load several jobs from the main central processing unit of a product, it saves battery consumption and provides an upward jump in its performance.

Most smartphone, tablet and wearable manufacturers including application developers are targeting mobile devices in the near future that will always be aware of their surroundings and activities. This will lead to providing meaningful results and content to the user. Inputs for the Always-on Context Awareness will be delivered by numerous sensors located within a mobile device, a separate micro-controller or a sensor hub fusing and computing their data.

PNI Sensor Corp. is making such a tiny 2×2 millimeter package as a sensor hub. It is by far the smallest, smartest and the lowest power-consuming implementation of a sensor hub. Consuming barely 200µA, this sensor hub implements the complete sensors function for the latest KitKat Version 4.4, as mandated by Google. Furthermore, PNI has incorporated all the KitKat functions without implementing an extra processor. This will greatly extend the battery lives of Android devices, even if they are using all their functions 24×7.

Android device manufacturers have two other choices. They could write their own fusion software and have them run on processors such as from Atmel or ARM. They could even license such software from others. On the other hand, OEMs could use smart sensors that have some functions implemented on-chip, while running the rest on the application processor. However, both the above methods are power-hungry and likely to consume up to ten times the power compared to the solution offered by PNI.

SENtral-K hub (the K standing for Google’s KitKat), from PNI can handle all the hardware connections from the MEMS sensors, while managing the virtual sensor functions in the software including the dedicated state-machine logic. The hub uses a tiny processor, the Synopsys ARC, along with specialized state-machines. Together, they achieve 140-thousand FLOPS or floating-point operations every second, while consuming less than 200µA at 1.8V. Being sensor agnostic, SENtral-K allows OEMs to select the lowest power consuming sensors from all different suppliers. This includes sensors such as for ambient light, pressure, proximity, magnetometer, gyroscope, accelerometers and many more.

SENtral-K combines all the outputs from the raw sensors and provides KitKat with the necessary functions it demands. These include functions such as step-detect, step-count, significant motion, linear acceleration including all the functions based on location and others that Google wants to incorporate at all times for their apps such as Google Now. The tiny chip comes fully pre-programmed to handle all functions demanded by Google’s KitKat 4.4.

For example, SENtral-K is capable of handling Android 4.4 KitKat functions such as those with nine degrees of freedom or DOF – 3-axis magnetometer, 3-axis gyro and 3-axis accelerometer. It can also handle six DOF – accelerometer and gyro or accelerometer and magnetometer. Other functions it can handle include Timestamp, Data Batching, Uncalibrated Sensor, Calibrated sensor, Significant Motion, Step Detect/Count, Linear Acceleration and Gravity.

Latest Trends in Sensors – Miniaturizations and Combinations

We see various sensors in smartphones and other gadgets. So far, most of the sensors were available only as discrete solutions – one sensor for one parameter. The latest trend is to combine several sensors into one package, cutting the overall cost of the sensors.

It is now commonplace to find several sensors in a package, for example, gyroscopes and accelerometers. In fact, now the majority of the market is for combo sensors of this type, and such combination sensors are a very important trend on the technology side.

Another trend catching on fast is miniaturization. As cell phones grow thinner and more goodies are increasingly packed within them, miniaturization of sensors is enabling some of innovative sensor packages and devices. Starting with the X-Box Contact, which brought in various sensors for delivering rich fidelity, we see them moving in into mobile devices as well.

Today, you can visualize fitness as seeing the key vital signs, and the visibility of biometrics is fast becoming a reality. Sensor miniaturization along with the enhanced fidelity of devices is allowing device manufacturers and service providers experiment with devices for offering and fulfilling compelling specific needs.

The MEMS sensor from Bosch has combined pressure, temperature and humidity measurement in a single component. This sensor, BME280, is meant for use in handsets and wearables. It provides greater control and is useful for people interested in fitness and sports. The humidity sensor senses and measures relative humidity ranging from 0-100%, between -40°C and +85°C and with a response time of less than one second. With an accuracy of plus or minus 3%, a hysteresis of 2% or more, the temperature reading of the sensor has an accuracy of 0.5% Celsius.

The pressure sensor of BME280 makes indoor navigation very simple. The device is sensitive to pressure changes of plus or minus one meter of altitude difference with a resolution of 1.5 cms and a relative accuracy of plus or minus 0.12 hPA. The 8-pin LGA packaging of BME280 measures 2.5×2.5 mm, a height of 0.93 mm and has I2C and SPI serial digital outputs. Bosch provides the BSH1.0 algorithm for developers to place a function for temperature compensation in the device.

Miniaturization can be seen in the new generation of sensors for infrared sensing that are now entering the smartphone bandwagon for night vision and surveillance. At CES this year, people really welcomed the idea of scanning the environment at night. For example, walking out to the car at night feels much safer if the area can be seen beforehand.

FLIR Systems Inc., have fitted an infrared sensor to one of their smartphone jackets. It is a heat camera, and the jacket is suitable for thermal imaging attachment for the iPhone 5 and the 5S. The screen displays temperature in different colors. For example, the hottest temperatures are shown in yellow, while the colder ones have a more purple hue. This is a very useful attachment for detecting insulation or moisture leaks in the home and for spotting people or wildlife at night. You can record video of heat images or its photographs at low resolutions.

Linear Position Sensor for Embedded Use

The launch of ME-7 Series Linear Position Sensors by the Alliance Sensors Group (Moorestown, NJ) facilitates a wide range of multiple applications. These sensors have been designed for embedded use suitable for measuring the ram position in hydraulic and pneumatic cylinders, in subsea, mobile or industrial applications. The ME-7 series is designed to be a functional replacement for embedded type magnetostrictive sensors with a drop-in form and fit for use. They can also be used as a replacement for embedded resistive potentiometers. Not only does the ME-7 series provide optimum accuracy, there is no wear-out involved. The design offers a number of unique features.

The ME-7 Series offers measurements ranging from four to 36 inches, which translates as 100 to 900 mm while operating at pressures of 5000 psi as well as at depths of 10,000 feet or 3,000 meters. The sensors are available with aluminum or stainless steel housing, both of which are categorized under IEC IP-67. The operating temperature is typically 85°C, but the series is also being offered with an operational temperature of 105°C as an optional feature. The analog output is in DC volts or current and these inductive sensors have been designed with the requirements of multiple applications in mind.

Although the Alliance Sensors Group has designed the ME-7 series to be highly robust, at the same time they have maintained the cost to a level that makes it affordable to the user. The technology used for ME-7 series is proprietary and known as contactless inductive sensing technology. It uses a 7 mm diameter solid probe requiring only a simple conductive tube target. This can be a simple gun drill ID of the cylinder rod that the operation is utilizing. This is considered better than a magnet or a special target type typically used by other sensors. The ME-7 series can replace an existing magnetostrictive sensor.

These sensors can be embedded at the same location that is configured for accepting magnetostrictive sensors. It is vital to note that the magnet from the magnetostrictive sensor need not be removed from its current place. The performance of ME-7 is not affected due to the presence of the magnet. Additionally, since the ME-7 series sensors are contactless, there is no wear and tear and the output signal is free from any deterioration. With the use of inductive coil in place of wires and the use of “time of flight” technology, the ME-7 series sensors are able to withstand shocks and vibrations in a more sustained manner.

The Alliance Sensors Group can justifiably claim that ME-7 series sensors have a very robust construction, are able to adapt to existing cylinder designs, offer higher resolutions as well as offer options for multiple analog outputs. There is no need for a target rod or magnet and the sensors have an infinite life, as they are free from any contact. It is expected that almost all users will be able to benefit from the ME-7 series in more than one way.

Pulse Ranging Technology Sensors Can Now Measure Distance

Radar measures the distance of an object by bouncing bursts of high frequency waves from the surface of the object and sensing the time it takes the echo to return. Pulse Ranging Technology or PRT sensors use a similar technique, but instead of using radio waves, they use bursts of light. The sensor emits bursts of light that travel to the object, bounce off its surface and return to the sensor. A processor in the sensor measures the time of flight of the light pulse and calculates the distance to the object.

PRT sensors emit light pulses of high-intensity at rates of 250 thousand pulses every second. The delay between the emission of light and its recapture increases with distance. Distances can also be measured by sensing the difference in phase shift of the reflected light from other types of photoelectric time of fight sensors that emit continuous light beams. The returning beam of light undergoes a change of phase because of reflection, and the difference in phase is a measure of the distance travelled by the light beam. However, a PRT sensor is superior in performance to other types of sensors.

Since a PRT sensor uses a pulsed laser diode, higher currents can be pumped into the laser source, resulting in light of higher intensity as compared to sources emitting continuous light. Light from a PRT sensor can be up to a thousand times more intense than that from other sources, which means they can easily detect objects further than 300 m.

High intensity light pulses from PRT sensors are not harmful to eyes. Although the light is intense, PRT sensors are off for longer periods that they are on. Therefore, in reality, PRT sensors emit very low power at any time compared to sensors sending out continuous light beams. In the market there are several PRT sensors certified as Class 1 laser products or “eye-safe.”

As pulsed light is easy to differentiate, PRT sensors are immune to other nearby photoelectric sensors, lighting and even sunlight. While sensing pulsed light, the PRT sensors can eliminate interference and crosstalk. On the other hand, sensors that use continuous light beams find light from stray sources often interfering with their readings.

PRT sensors are very useful in measuring continuously changing positions of the target. For example, they can monitor the stack height of metals; check if a container has been filled up to a specified height; and position a load or a product properly. They are good in preventing collisions of cranes, gantry and conveyors. Some PRT sensors can convert the distance measurement to streams of binary digits via Profibus, Ethernet or IO-Link, while some can output analog signals as well.

PRT sensors are useful not only for distance measurements, but also for detecting the presence/absence of objects. For example, they can verify rack occupancy in warehouses, detect stacks or panels within a defined window, tell when spools or rolls are either empty or full and check the height of a forklift truck. Moreover, designers can set the range at which the sensor will start detecting objects.