Motion-sensing thin low-power Bluetooth beacon solution for smart tags

The beacon is a battery-powered miniature Bluetooth radio transmitter. It functions like a lighthouse, which can be seen by everyone within a certain range. What these small hardware devices have always transmitted is not light, but Bluetooth Low Energy (BLE) data packets. With the use of the corresponding interactive application in the smart device to scan, these low energy Bluetooth data can be presented in any modern smart phone device with a built-in Bluetooth transceiver.

The beacon is a battery-powered miniature Bluetooth radio transmitter. It functions like a lighthouse, which can be seen by everyone within a certain range. What these small hardware devices have always transmitted is not light, but Bluetooth Low Energy (BLE) data packets. With the use of the corresponding interactive application in the smart device to scan, these low energy Bluetooth data can be presented in any modern smart phone device with a built-in Bluetooth transceiver.

Beacons provide a low-cost broadcast solution that can operate autonomously for a long time. In addition, when used in a building, for example, no additional technology is needed because everything can be integrated into the same ecosystem of the wireless network. In addition, through some additional functions, the concept of low-power Bluetooth beacon broadcast messages can be extended to make it applicable to other fields.

In this white paper, we will show how beacons can support extended functions through the use of a series of peripheral devices to allow them to process and Display data while maintaining autonomous operation.

Motion-sensing thin low-power Bluetooth beacon solution for smart tags
Figure 1: Example of BLE ecosystem

A typical low-power Bluetooth ecosystem is shown in Figure 1. This example shows an application close to marketing. Among them, the deployed beacon broadcasts the ID number at a rate of about 10 times per second through the Bluetooth low energy channel. When a Bluetooth device (such as a smart phone) placed near the beacon receives this ID number, the application recognizes this ID number, and it links it to an operation. This operation can be a simple operation such as displaying marketing offers on a smartphone, or it can be a more complex task, such as an application.

Other use cases for Bluetooth low energy beacons include but are not limited to:

Indoor navigation: GPS signals are sometimes very weak when indoors. The BLE beacon network can be used for accurate positioning in indoor places such as shopping malls, museums, and airports.

Smart labels: It is especially popular in large retail stores. Traditional labels can be replaced with beacons. Realizing the smart label mechanism can greatly reduce the time and manpower required to update product prices and launch new offers.

Healthcare: BLE beacons can greatly improve healthcare by reducing patient waiting time and informing doctors of the patient’s medical history, including medications, medical equipment tracking (asset tracking), injection equipment, patches, etc.

Figure 2 shows an example of indoor navigation and smart tag applications, using BLE beacon technology to guide and notify visitors.

Motion-sensing thin low-power Bluetooth beacon solution for smart tags
Figure 2: Example of BLE beacon application for indoor navigation/smart label application

Figure 3 shows an example of a healthcare application based on BLE beacons. In this example, important readings of the patient can be viewed and accessed remotely.

Motion-sensing thin low-power Bluetooth beacon solution for smart tags
Figure 3: Examples of BLE beacon applications in healthcare applications

Without additional hardware, such as motion sensors or visual aids, traditional Bluetooth low energy beacons cannot support these use cases. A version with extended functions is required. In this article, we propose a BLE beacon solution with extended functions, including its important peripherals: thin batteries, motion sensors, and user interface components (LCD, buttons). We will introduce these peripherals in detail in the next section.

This white paper also outlines the use of flexible PCB technology to make Bluetooth low energy beacons. This is a key requirement put forward by some segmented applications, such as smart labels, pharmaceutical product applications, wearable devices, medical applications, etc.

1.1. Flexible PCB technology

Flexible circuit adaptation has the following advantages:

Dynamic bending: Flexible circuit has excellent bending or moving ability. This feature helps to maintain a connection with a device that can be stretched, contracted, or retracted during the application. This is a very useful advantage of flexible PCB technology in wearable and medical applications where space is very limited.

Reliability: Flexible circuits have excellent performance and reliability records in demanding medical applications. Its basic advantage is to eliminate connection points, simplify assembly, and reduce the risk of interconnection failures (such as poor solder joints), thereby improving reliability and durability.

Space and weight: The recent increasing demand for smaller and lighter devices makes flexible circuits an ideal choice for applications that have high requirements for space and weight. The flexible circuit is ultra-thin and can be easily bent to fit almost any surface. Compared with standard rigid PCB boards, flexible circuits are also lighter.

Cost: Since flexible circuits can reduce the number of connections required to a minimum, they can be efficiently mass-produced, which helps reduce assembly costs. Avoiding the use of solder wires, rigid printed circuits and connectors provides the possibility to further reduce the total cost.

2. Overview of Bluetooth Low Energy Beacon System

A beacon BLE system with extended functions usually consists of the following main components:

・ Bluetooth Low Energy SoC Unit: A Bluetooth connection system-on-chip (SoC) with a built-in microcontroller unit (usually an ARM processor) for necessary computing tasks. The choice of the main processor depends on the type and complexity of the device. Modern MCUs integrate most functions in a single chip. The BLE SoC has an additional antenna that broadcasts at a specific wavelength and frequency.

・Battery: BLE SoC should be able to run for a long time, which is achieved by using a suitable battery power supply. Button batteries have proven to be a comprehensive and effective solution for cost, size and duration. It is generally not recommended to use rechargeable batteries, because a dedicated circuit is required to support the charging operation, resulting in increased costs.

・ Motion sensor: You can use a motion sensor with an accelerometer to extend the battery life and increase the autonomy of the system by introducing the system sleep mode function when no motion is detected. Of course, this optional function depends on the application scenario of the beacon.

・ User interface: According to the application scenario, various man-machine interface options can be considered in the beacon:

Low-power displays, such as Electronic paper technology, have the advantage of continuously displaying a single image after a complete power failure, which is very useful for retail store label applications.

Mechanical buttons can be used as part of the on/off mechanism to further extend battery life.

2.1. BLE beacons with extended functions, low power consumption, and flexibility

Motion-sensing thin low-power Bluetooth beacon solution for smart tags
Figure 4: Circuit block diagram of a beacon device with extended functions

Figure 4 depicts the top-level block diagram of a BLE beacon device with extended functions, including:

Bluetooth Low Energy (BLE) SoC, using microprocessor unit ARM Cortex M0 for data transmission
Large-capacity SPI flash memory
Accelerometer/gyro sensor
32MHz crystal oscillator
On/off power switch

Taking into account the limited Display drive capability of the BLE SoC, it is also possible to connect a low-resolution e-paper color display to the beacon system

3. Hardware components and implementation

In addition to providing extended functions, Dialog’s BLE beacon solution also supports the flexibility of key components. PCB, battery, and LCD are all made of flexible materials, allowing them to be placed on most non-planar surfaces, which is especially important for smart label applications.

Another key aspect of the BLE beacon is that all its active components should exhibit very low power consumption to support long battery life.

3.1. DA14531 BLE SoC from Dialog semiconductor

In the example shown in this article, we need a small size BLE MCU solution with very low power consumption. Therefore, we chose DA14531 BLE SoC, which is one of the small size Bluetooth 5.1 system-on-chip (SoC) solutions. It has a record-breaking low sleep and operating power consumption, even using a small battery can ensure a long operation and shelf life. DA14531 adopts a small package of 2.0 x 1.7 mm, based on a powerful 32-bit ARM Cortex M0+, with integrated memory and a complete set of analog and digital peripherals.

Motion-sensing thin low-power Bluetooth beacon solution for smart tags
Figure 5: DA14531 circuit block diagram

The main hardware components of the BLE beacon system with extended functions are analyzed as follows:

3.2. Flexible electronic paper display

For smart label applications, thin and low-power displays are required. E-paper displays are suitable for beacon use cases with extended functions, as these displays only consume power when refreshed. As long as the image is displayed, the electronic paper display does not need to consume additional electricity to maintain the display state of the image, which greatly extends the battery life of the product.

For the example described in this article, we chose an all-in-one display. This type of display does not require a negative power supply (negative power supply requires additional complex and expensive circuits to achieve), thereby reducing the overall material cost. The display resolution is 212*104 pixels, and the 24-pin FPC connector is used to connect to the main MCU through the SPI interface.

3.3. Bosch Sensortec sensor

In order to increase motion intelligence and further reduce the power consumption of the system, motion sensors need to be added. In this article, we are using Bosch BMI270. This is an ultra-low-power motion sensor that combines an accelerometer and gyroscope, with multiple operating modes and self-calibration algorithms. BMI270 is a very good choice for this purpose, because it integrates many functions required by the extended beacon. In addition, its ultra-small size and few external components make it ideal for use in flexible systems.

3.4. Flexible battery

In a flexible beacon system, a flexible battery is also required. In the system example in this article, the advanced solid-state battery newly introduced by Imprint Energy is used. This battery material (Zinc poly) can achieve high-energy, safe and stable ultra-thin operation, making it an ideal choice for BLE beacon applications because it can be printed into any shape without additional sealing. This battery has a very low internal resistance, can withstand high current pulses for a long time, and provides a nominal capacity of 15mAh. These features make this battery an option for beacon applications with extended functions.

3.5. DA14531 flexible BLE beacon with actual extended functions

Figures 7 and 8 show the top and bottom views of the assembled flexible PCB, which deploys the DA14531 beacon system described in Chapter 3 of this article. These two pictures also indicate the location of all the main components introduced in the previous chapters. The total thickness of the flexible PCB is 0.23 mm. The base material is polyimide, and its characteristics are shown in Table 1. The maximum height of the entire structure (PCB and peripherals) is approximately 2 mm, taking into account the high components on each side, namely the Inductor (top) and the display connector (bottom). Most of the surface thickness is lower than this figure, and the flexible material of the circuit board makes it highly adaptable and bendable, making it suitable for any type of housing. The flexibility of the entire BLE beacon (PCB, electronic paper, battery assembly) is shown in Figure 9.

4. Power and RF measurement part

As a battery-powered design, DA14531 flexible beacon should have ultra-low power consumption, so that it can provide a long working life. Figure 10 shows the total power consumption value measured at a level of approximately 500 uA (average). The measurement was carried out under the following conditions:

E-paper display in screen refresh mode

BLE broadcast interval is 2 seconds

Scan mode events for nearby tag devices

The accelerometer is running, and the output data rate is 1.5 Hz

Shows the total power consumption value at 160 uA (average) level, under the same conditions as above, excluding screen refresh events.

In sleep mode, extremely low power consumption is essential, as this is the default operating state of this type of beacon. For this solution, the sleep current measured on the static (fixed) picture on the electronic paper display is 3.9 uA.

In Figure 12, there is the reflection coefficient of the flexible polyimide PCB material described in Table 1. The reflection coefficient -28dB of the matched antenna is almost the same as the standard non-flexible PCB FR4 material, so the polyimide material used has good radio frequency performance.

5 Conclusion

This article introduces a low-power, extended-function BLE beacon system based on Dialog Semiconductor’s DA14531 BLE SoC. The focus is on the flexible material PCB, which has higher reliability, saves costs, and it is important to adapt to any surface due to its flexibility. In addition, the flexible materials of the battery and the electronic paper display components make this low-power Bluetooth beacon with extended functions an ideal choice for applications such as healthcare and smart labels.