As a driver, I’ve spent more time cursing a faulty tire pressure sensor that causes an unnecessary dash alert than appreciating the complex technology in each of my four tires. When they work properly, tire pressure sensors help you maximize fuel efficiency and avoid dangerous tire blowouts. However, these highly integrated sensor devices can be used in many other applications far beyond the automotive industry.
How Does a Tire Pressure Monitoring System Work?
As the astute driver will have noticed, there is no wire running from your car into your tires. You have also never had to electrically charge your tires. How, then, does your car know when your back right tire pressure is a little low? Starting in 2007, all tires and vehicles have to be TPMS enabled so every new tire you put on your car contains a module that senses various aspects of your tire and wirelessly communicates the information to the car’s brain. The details vary between systems and automotive manufacturers, but the basic block diagram is shown below:
At a high level, this block diagram could represent a wide range of IoT devices. Almost all smart sensors are battery powered and need the sensor, microcontroller, and transmitter blocks to respectively collect, process, and transmit data. Tire monitoring modules employ pressure sensors at a minimum, but many also incorporate temperature sensors and multi-axis accelerometers to give supplementary environmental and position data.
Wireless Tire Pressure Monitor Module
These modules are designed to survive for years (the entire lifespan of your tire) off a single battery and are thus designed to consume as little power as possible. They need to be incredibly rugged, as they must endure the same shock, vibration, stresses, and temperature swings as the rest of the tire. Through it all, they must transmit data an average of every 90 seconds while the vehicle is running. They have the advantage of being in close range of the wireless receiver, which is often mounted in the body of the vehicle right above the tire, but typically operate at low sub-GHz frequencies that can actually travel very long distances.
Semtech’s LoRa (long range) wireless communication protocol is gaining momentum and is advertised as being able to send small packets of data several kilometers at low frequencies like 433MHz. The data sent by your average TPMS is a whisper rather than a long-distance shout in order to conserve power and not confuse the sensors of neighboring vehicles, but the transmission block tends to be configurable by the designer, and all you need is a frequency matched receiver to read the data.
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So, once you take these modules out of their native environment, you have a low cost, highly efficient and integrated wireless sensor that can handle just about any environment. Does that spark any ideas? Here are a few of ours:
Tire Pressure Monitor Sensor in Drones
This application definitely involves increasing the transmitter power or changing the front end entirely if you want to read data from the ground, but it is worth the effort. If you simply want to record flight data to be pulled after landing, you do not even need to use the wireless portion. Drones need accelerometer data to stay airborne, and they can use an air pressure sensor as a rudimentary altimeter. Advanced modules like the FXTH870 family from NXP Semiconductor have two temperature sensors – a low-accuracy sensor that can be used to trigger an interrupt once a threshold is crossed and a high-accuracy sensor that consumes more power.
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This can be used to do something as simple as send an alert if your drone experiences a dramatic temperature swing in flight, which can indicate a serious problem or unsafe flight conditions. Even if you choose to use this module for quite a bit of data, the microcontroller is so efficient at packaging and transmitting data that you should not experience significant battery drain. The modules are so power conscious that battery level is often a parameter the microcontroller expects to send to the vehicle brain, whether the vehicle is automotive or aerial.
Tire Pressure Monitoring System in Smart Toys
Whether we are talking about human babies or pets, we live with the universal truth that playtime is important but must occur on their terms. We’ve all lived with that one electronic toy that is intended to stimulate some particular impulse to better engage a child or pet and works well for a bit, but then squawks dejectedly in the corner once the subject gets distracted and the toy seems more frightening than enticing. Tire pressure monitoring systems do everything they can to reduce power consumption and go into deep sleep when the car is not in motion.
The modules use the built-in accelerometer to tell when the car turns on to wake up and start sensing, but they could easily use the same functionality to detect the interested nudge of a toddler’s hand or terrier’s nose. If the toy does not light up/make noise/move unless approached, the experience is likely to be much more positive for everyone involved and to encourage higher levels of engagement down the road. Most TPMS modules operate off the same 3.3V supply as simple microcontrollers, buzzers and LEDs, and can measure temperature and pressure data to capture information about how the toy is being used. Is your toddler growing up and starting to grip harder? Or, if you have a dog, is the smart toy buried out in the snow?
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Other TPMS Uses: Sport Equipment and Wearables
Speaking of dogs, they don’t wear shoes. We do. Yet, we often go out into the world together and experience the same environment. By the time your furry friend lets you know they are unhappy, they may have already burnt the pads of their feet or been exposed to extreme cold. Even on a board with a battery and antenna, a TPMS could easily mount to the outside of a shoe. In addition to using the vibration sensor for step count, you could receive an alert on your phone if the ground temperature is outside of the safe range for your pet. With a little programming, you could leave your smartphone out of the equation entirely and use the available GPIO to light up an LED when the range is exceeded.
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The built in accelerometer and pressure data can be a great tool for monitoring sports equipment like bats and rackets, especially with their extremely rugged construction. While the modules are typically not waterproof because water should not be inside your tires, they can handle high accelerations, vibrations, and generally being abused to the same extent as sport or gym equipment. Changes in pressure can also be used to measure various aspects of athleticism, like how hard a large ball can be thrown or a punching bag can be hit.
So Much More…
Where else would you want to use a smart sensor that is built to last for years on a single battery? If you’re feeling inspired, browse interactive reference designs that can help you get started and get sensing!