author

Nikolaos Terzopoulos, Senior Hardware Engineer, Dialog Semiconductor;

Marios Iliopoulos, Director of Applications, Dialog Semiconductor;

Panagiotis Rozos, Hardware Applications Manager, Dialog Semiconductor;

Athanasios Nikou, Junior Hardware Applications Engineer, Dialog Semiconductor

1. Abstract

The beacon is a tiny battery-powered Bluetooth radio transmitter. It functions like a beacon that can be seen by everyone within a certain range. Instead of light, these small hardware devices have been transmitting Bluetooth Low Energy (BLE) packets. Combined with scanning using the corresponding interactive app in the smart device, these Bluetooth LE data can be presented on any modern smartphone device with a built-in Bluetooth transceiver.

Beacons provide a low-cost broadcast solution that can operate autonomously for long periods of time. Furthermore, when used inside buildings, for example, no additional technology is required, as everything can be integrated into the same ecosystem of wireless networks. In addition, with some additional functions, the concept of Bluetooth low energy 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 functionality through the use of a range of peripherals to allow them to process and display data while maintaining autonomous operation.

Figure 1: Example of BLE Ecosystem

A typical Bluetooth low energy ecosystem is shown in Figure 1. This example shows an application case of proximity 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 smartphone) placed near the beacon receives this ID number, the application recognizes this ID number and it links it to an action. This can be something as simple as displaying a marketing offer on a smartphone, or it can be performing a more complex task like downloading an app.

Other Bluetooth low energy beacon use cases include, but are not limited to:

Indoor Navigation: GPS signal can sometimes be very weak indoors. The BLE beacon network can be used for accurate positioning in indoor places such as shopping malls, museums, airports, etc.

Smart labels: Especially popular in large retail stores, traditional labels can be replaced with beacons, enabling a smart label mechanism that minimizes the time and labor required to update product prices and launch new offers.

Healthcare: BLE beacons can greatly improve healthcare by reducing patient wait times and informing physicians of patient medical history, including medications, medical device tracking (asset tracking), injection devices, patches, and more.

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

Figure 2: Example of BLE beacon application for indoor navigation/smart tag applications

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

Figure 3: Example of a BLE beacon application in a healthcare application

Traditional Bluetooth low energy beacons cannot support these use cases without additional hardware, such as motion sensors or visual aids. A version with extended functionality is required. In this paper, we propose a BLE beacon solution with extended functionality, including its most important peripherals: thin battery, motion sensor, and user interface components (LCD, buttons). We will describe these peripherals in detail in the next section.

The use of flexible PCB technology to manufacture Bluetooth low energy beacons is also outlined in this white paper. This is a key requirement raised by some segmented applications, such as smart labels, pharmaceutical product applications, wearable devices, medical applications, etc.

1.1 Flexible PCB Technology

Flexible circuit fitting offers the following advantages:

Dynamic Bending: Flexible circuits have excellent ability to bend or move. This feature helps to stay connected with devices that can stretch, contract or retract during 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 a proven track record of performance and reliability in demanding medical applications. The fundamental advantage is that it eliminates connection points, simplifies assembly, and reduces the risk of interconnect failures such as poor solder joints, resulting in increased reliability and durability.

Space and Weight: The recent increase in demand for smaller, lighter devices makes flex circuits ideal for applications where space and weight are critical. Flexible circuits are ultra-thin and can be easily bent to fit almost any surface. Compared to standard rigid PCB boards, flex circuits are also lighter.

Cost: Because flex circuits can minimize the number of connections required, they can be efficiently mass-produced, which helps reduce assembly costs. Avoiding the use of soldered wires, rigid printed circuits and connectors offers the potential to further reduce overall costs.

2. Overview of Bluetooth Low Energy Beacon System

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

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

Battery: The BLE SoC should be able to run for a long time, which is achieved by using a suitable battery power source. Coin cells have proven to be the most efficient solution for a combination of cost, size and duration. The use of rechargeable batteries is generally not recommended because of the added cost of requiring dedicated circuitry to support the charging operation.

Motion Sensor: A motion sensor with an accelerometer can be used to extend battery life and improve system autonomy by introducing a system sleep mode feature when motion is not detected. Of course, this optional feature depends on the application scenario of the beacon.

User Interface: Depending on the application scenario, various HMI options can be considered in beacons:

Low-power displays, such as e-paper technology, have the advantage of continuously displaying a single image after a complete power outage, making them useful for retail store labeling applications.

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

2.1 Low-power, flexible BLE beacon with extended functions

Figure 4: Circuit block diagram of beacon device with extended functions

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

Bluetooth Low Energy (BLE) SoC with microprocessor unit ARM Cortex M0 for data transfer

Large capacity SPI flash memory

Accelerometer/Gyro Sensor

32MHz crystal oscillator

On/Off power switch

Considering the limited display driving 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 functionality, Dialog's BLE beacon solution supports flexibility in key components. PCBs, batteries and LCDs are all made of bendable materials, enabling them to be placed on most non-planar surfaces, which is especially important for smart label applications.

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

3.1 From Dialog Semiconductor

DA14531 BLESoC

In the example shown in this article, we need a small form factor BLE MCU solution with very low power consumption. Therefore, we chose the DA14531 BLE SoC, which is one of the smallest Bluetooth low energy 5.1 system-on-chip (SoC) solutions in the world. It features record-breaking low power consumption for sleep and operation, ensuring long operation and shelf life even with the smallest disposable batteries. Housed in a small 2.0×1.7mm package, the DA14531 is based on a powerful 32-bit ARM Cortex M0+ with integrated memory and a complete set of analog and digital peripherals.

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, low-profile, low-power displays are required. E-paper displays are best suited for beacon use cases with extended functionality, as these displays only consume power when refreshed. As long as the image is displayed, the e-paper display does not need to consume extra power to keep the image displayed, which greatly prolongs the battery life of the product.

For the example described in this article, we chose an all-in-one display. Such displays do not require negative power supplies (which require additional complex and expensive circuitry to implement), reducing overall bill of materials costs. The display resolution is 212*104 pixels, and it is connected to the main MCU through the SPI interface using a 24-pin FPC connector.

3.3 Bosch Sensortec sensors

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 the Bosch BMI270. This is an ultra-low-power motion sensor that combines an accelerometer and gyroscope with multiple operating modes and self-calibration algorithms. The BMI270 is a very good choice for this purpose as it integrates many of the functions needed to expand the beacon. In addition, its ultra-small size and few external components make it ideal for use in flexible systems.

3.4 Flexible battery

In flexible beacon systems, flexible batteries are also required. In the system example in this article, Imprint Energy's latest advanced solid-state battery is used. This battery material (Zinc poly) enables high-energy, safe and stable ultra-thin operation, making it ideal for BLE beacon applications as it can be printed in any shape without additional sealing. This battery has very low internal resistance, can withstand high current pulses for a long time, and offers a nominal capacity of 15mAh. These characteristics make this battery an excellent choice for beacon applications with extended functionality.

Figure 6: 15mAh Zinc Poly flexible ultra-thin battery

3.5 Actually with extended functions

DA14531 Flexible BLE Beacon

Figures 7 and 8 show top and bottom views of the assembled flex PCB deploying the DA14531 beacon system described in Section 3 of this paper. The two figures also indicate the location of all the major components described in the previous chapters. The total thickness of the flex PCB is 0.23mm. The base material is polyimide, and its properties are shown in Table 1. The maximum height of the entire structure (PCB and peripherals) is about 2mm, taking into account the tallest components on each side, namely the inductor (top) and the display connector (bottom). Most surface thicknesses are below this figure, and the board's flexible material makes it very adaptable and bendable, allowing it to fit into any type of enclosure. The flexibility of the entire BLE beacon (PCB, e-paper, battery components) is shown in Figure 9.

Table 1: Polyimide Material Properties

Figure 7: DA14531 BLE Beacon – Top View

Figure 8: DA14531 BLE Beacon – Bottom View

Figure 9: Placing a flexible BLE beacon on an actual circular (non-planar) surface

4. Power and RF Measurement Section

As a battery-operated design, the DA14531 flexible beacon should have ultra-low power consumption, allowing it to provide a long operating life. Figure 10 shows the total power dissipation measured at a level of approximately 500uA (average) 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 1.5Hz

Figure 10: Total power consumption of the DA14531 flexible beacon

Figure 11 shows the total power consumption figures at the 160uA (average) level, under the same conditions as above, excluding screen refresh events.

Figure 11: Total power consumption of the DA14531 flexible beacon, excluding screen refresh

Very low power consumption is critical in sleep mode, as this is the default operating state for such beacons. For this scheme, the measured sleep current of a static (fixed) picture on the e-paper display is 3.9uA.

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

Figure 12: S11 amplitude (in dB)

5 Conclusion

This article describes a low-power, extended-capability BLE beacon system based on Dialog Semiconductor's DA14531 BLE SoC. The focus is on flexible material PCBs, which offer higher reliability, cost savings, and most importantly, adaptability to any surface due to their flexible properties. Additionally, the battery's flexible materials and e-paper display components make this Bluetooth low energy beacon with extended capabilities ideal for applications such as healthcare and smart labels.

Reviewing Editor: Tang Zihong

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