Development of sensors with Bluetooth low energy radio interface

Introduction

Using radio standards Bluetooth and WiFi for interfacing various equipment with computing power and user interface of smartphones reduces the cost of the product and increase its attractiveness to the consumer. But the new Bluetooth low energy technology has one more feature that opens up the possibility of its use in small autonomous sensors.

The main difference between the core Bluetooth 4.0 from the previous specifications is ultra-low power consumption. This feature allows battery-operated devices to function for several years without replacing batteries, and also reduces the size of the end device for convenient use in the areas of healthcare, physical education and sports, security systems and home entertainment.
Bluetooth wireless technology with low power consumption appeared relatively recently in the composition of smartphones and tablet computers. The first manufacturer to implement the appropriate hardware and software in their devices was Apple. Bluetooth low energy support was received by smartphones starting with iPhone 4S and tablets starting with iPad 3. At the moment, Google and Google starting at Android 4.3 and Microsoft starting at Windows Phone 8.1 support the technology.
Assessing the range of manufactured wireless sensors, I was convinced of the widespread use of low-power radio channels of various standards in the domestic sphere and in industry, but for Bluetooth 4.0 technology there was no well-deserved number of implementations and I set myself the task to bring to the market a line of devices that take advantage of the new Bluetooth stack , choosing three areas for development:

1. Ultrasonic level gauge;
2. Tire pressure measuring system;
3. Sensors for the registration of movements.

Ultrasonic level gauge

Existing level measurement systems in tanks have high prices, and installation and adjustment can cause difficulties requiring the involvement of qualified specialists.
In my design, the drawbacks of existing gauges are eliminated due to the combination of the following features:

1. The distance is measured using an ultrasonic piezoelectric transducer. An inexpensive hermetic sensor is used that is not sensitive to contaminants of the radiating surface.
2. The data on the distance between the sensor and the surface of the medium is transmitted via the Bluetooth low energy radio channel to a smartphone or tablet, the display of which shows the degree of filling of the tank in an intuitive graphical form. No additional display device is required, which reduces the cost of the system.
3. The piezoelectric transducer, Bluetooth radio module and lithium battery of CR2032 standard size are combined into a compact sealed plastic case, the design of which is designed taking into account the installation features on most types of capacitances. Labor costs for installation and configuration are minimal, no wiring is required. The device complies with IP67 dust and moisture protection class. No additional protection is required.
4. The estimated duration of the continuous operation of the sensor from one CR2032 battery at a measurement frequency of 10 times per day is at least 3 years. The frequency of maintenance of the sensor is minimized, although the design of the case and adapted for quick replacement of batteries.

The range of the Bluetooth radio channel is sufficient to obtain data on the degree of filling, being far from containers, eliminating hazards and discomfort during measurements.

I made prototypes of two modifications of sensors, conducted field tests of devices in a large volume and placed the corresponding application in the App Store .

Tire pressure measuring system

Do I need to list how many troubles are fraught with the operation of vehicles at tire pressures that are significantly different from those recommended by the manufacturer? Visually or according to the behavior of the car, the pressure in the wheel cannot be determined with sufficient accuracy, and that is why in many countries there are laws on the mandatory equipment of all new vehicles with TPMS systems. But if the car is not equipped with a standard system and there is an objective need for it, then the only way out is to install a third-party TPMS system.
There are many such systems on the market, but there is not a single TPMS where information from sensors is transmitted directly to the user's smartphone. Additional display devices or a repeater-Bluetooth sensors increase the cost of the system, clutter up the instrument panel or occupy the cigarette lighter socket, bringing the element of "collective farm" into the car's interior.
I propose to use sensors with a Bluetooth low energy radio channel, which will eliminate the listed disadvantages of existing TPMS systems.

Sensors for motion detection

The next application of Bluetooth low energy technology is to build a security system or a system for collecting statistical information that is scalable over a wide range, based on miniature autonomous acceleration sensors.

In security systems, the following advantages of such sensors over the well-known infrared motion sensors and wired access control sensors allow simplifying the installation procedure on a controlled object, making it invisible to potential intruders:

1. There is no need for a direct line of sight between the surface of the device and the surrounding space. Sensors can be installed inside controlled objects, be hidden under radio-transparent surfaces.
2. Wireless reading of displacement events allows you to get rid of the unmasking effect of wires.
3. No building of an alarm system is required. All sensors available at the security site can be remotely polled from a regular smartphone or tablet.

In addition to security systems, displacement sensors can be used to detect emergency levels of vibration of machinery and mechanisms, as well as to collect specific statistical information when using video recording equipment is unethical or illegal.
An application installed on a smartphone or tablet analyzes the information collected from the sensors and displays it to the user in the form of a graphical diagram.

At the moment, prototypes of displacement sensors have been created, all algorithms have been debugged, and long-term tests of devices have been conducted. An application is being developed for the iOS operating system.
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Conclusion

The reason for the publication of this material on "Habrahabr" is the need for a professional assessment of my development by people employed in the high-tech industry.
Perhaps someone is already developing such devices. In this case, it will be interesting to find out in what ways numerous design tasks were solved. I will also gladly share my experience.
It remains an open question to choose a device that can combine sensors based on Bluetooth low energy into a single system. It seems to me a kind of embedded single-board computer running an open operating system and having Bluetooth low energy hardware on board. His task is to collect data from the sensors and send them to the server. The computer should also have an emergency GSM data transmission channel to the user in case of problems with the main way of informing.