Making sense out of sensors in IoT development
Today’s IoT devices pack a ton of functionality, so it’seasy to overlook their smallest components. Among those are sensors, whichserve as tiny building blocks for Ambient Computing,that acquire and convert measurements of the real world into digital data. Mostdevelopers are aware of common sensors such as the accelerometer and gyroscopefound in smartphones. However, sensors have been used in industrialapplications for decades, and have recently gained prominence with the growthin IoT and Industrial IoT (IIoT).
Since developers have been integrating sensors withQualcomm Technologies solutions through mechanisms like our Qualcomm Hexagon DSP,we thought it would be beneficial to discuss the different types and categoriesof sensors available, how sensors work, and considerations when choosing them. AMR expects the global opportunity forsensors to reach $241B by 2022, so it’s definitely an area to stayon top of.
Where the real world meets the digital world
As you start to work with sensors, it’s important to notethe definition of a sensor, and that the classification of sensors by differentdevelopers, can vary. A sensor can be the tiny component itself, or acombination of sensors that collectively provide data. For example, a solutionpackaged with sensor components, a microcontroller, and connectivity, could becalled a “sensor” or an “intelligent sensor”. Even technologies such assmartphones and drones are sometimes referred to as sensors.
Sensor measurement categories
Sensors measure Degrees of Freedom (DoF) of the realworld in six general categories:
o Mechanical: force,velocity, acceleration, etc.
o Thermal: temperature, entropy, etc.
o Chemical: composition, reaction rate,etc.
o Radiant: electromagnetic wave intensity,phase, etc.
o Magnetic: field intensity, flux, etc.
o Electrical: voltage,current, resistance, etc.
In general, a sensor consists of a mechanism that reactsto real-world phenomenon causing measurable electrical phenomenon (e.g.,voltage). Common real-world phenomena or “degrees of freedom” (DoF) are listedhere.
As you can see, there are many different types ofsensors, and they can vary in size and function. The table below identifiessome of the most common sensors used in Ambient Computing solutions likesmartphones, VR headsets, wearables, and IoT.
The design of the sensor matters
Sensor designs vary widely, and there are usuallymultiple techniques to measure a certain phenomenon.
Take for example, an accelerometer. One technique tomeasure acceleration is to track the piezoelectric effect that occurs whenmicroscopic crystals generate a voltage from the stress caused by accelerativeforces. An alternative approach is to measure differences in capacitance that occurwhen forces are applied between microstructures.
Another example is a temperature sensor. One such designuses a thermocouple in which two dissimilar metals are joined at two ends,where one end is used to take the measurement. When the temperature at the twoends differs, a voltage is created. A completely different design involves aresistance thermometer detector (RTD) such as wire-wound film. Here, anelectrical current is applied across the RTD causing a change in the resistancelevel that corresponds to a temperature.
Sensors may be hardwired to another part of a system ormay be wireless. In the latter case they may be combined with other digitalcircuitry to send their measurements over the air and may contain their ownpower source. A sensor may be a simple standalone measuring device that must beconnected to other digital hardware, such as an integrated circuit, to consumethe measurement. Or, it may be combined with the digital hardware duringmanufacturing to form a single package.
Virtual sensors and sensor fusion
Sensors and other micro devices can be used in differentways to form “virtual sensors” that provide new or alternative methods ofmeasurement. For example, Elliptic Labs usesa device’s speaker and microphone in conjunction with our Qualcomm? NeuralProcessing SDK, to create a virtual sensor that detects movementusing sound.
Another approach is “sensor fusion” where an algorithmanalyzes signals from multiple sensors to compute results. Fusion can deriveinformation that wouldn’t be possible or complete from using just a singlesensor or micro device. For example, data from an accelerometer, gyroscope, andcompass can be “fused” to estimate geocoordinates when GPS connectivity islost.
Data from sensors can also be combined by business logicto provide information. For example, this Smart Vineyard Demo runningon the DragonBoard 410c usestemperature, light, and moisture sensors to provide environmental data on whichto base intelligent agricultural decisions.
Making smart choices with sensors
When choosing a sensor there are often trade-offs toconsider, so it’s important to analyze your business requirements, the targetoperating environment, and the following sensor characteristics:
o accuracy: how closely the sensor’smeasurements match the true value of a phenomenon
o precision: the ability of a sensor toreproduce a measurement,
o designated operating environments
o type of mechanical components used totake measurements and the pros and cons associated with the use of suchmechanisms
o reliability ratings throughout itsexpected life span
Finally, check for compatibility between the device’sphysical connections and those of your project. For example, the mezzanine board forthe DragonBoard 410c offers a variety of interface options such as I2C, GPIO,and SPI, as well as voltage level shifting.
Sensing the next big thing in IoT development
Sensors allow devices to bridge the real world with thedigital world. If you’ve used sensors in new and creative ways, consideruploading the details to our QDN Projects page, orsearch through the projects already posted for some for inspiration on whatother developers may be doing with sensors. If you are just starting to usesensors with the DragonBoard 410c, we encourage you to check out the valuableresources available with 96 Boards.We’ll be taking some deeper dives on sensors and development in future blogs,so check back often if you’re interested in more details.