Accelerating Development of Ambient-Powered, Beacon-Based Solutions

Beacon technology offers compelling opportunities for assistive applications across diverse market segments including retail, transportation, and hospitality industries. As companies rush to deliver beacon-based solutions to a fast-moving marketplace, beacon designers face growing demand for faster delivery of these small wireless devices and greater expectations for extended, maintenance-free operation. By combining wireless processors with specialized energy-harvesting ICs, engineers can rapidly create beacon designs capable of operating for years without battery replacement.

Beacons are emerging as an increasingly important element in strategies intended to offer location-based assistance to individuals — helping to guide passengers through airports, guests to hotel rooms, and even baseball fans to better seats. In retail, beacon technology is seen as a powerful catalyst to help influence shoppers in selecting products on the store floor (Figure 1).

Figure 1: Small Bluetooth-based devices are rapidly gaining attention for their ability to influence sales in retail and offer location-based services across diverse market segments. (Courtesy of Nordic Semiconductor)

In fact, market analyst BI Intelligence forecasts that beacons already directly influenced over $4 billion in US retail sales in 2015 and will influence ten times that amount in 2016 alone. Another analyst firm ABI predicts that by 2018, over 800 million smartphones will be relying on beacons for indoor location, achieving the same level of usage in smartphone apps as GPS provides today. Indeed, with its ability to leverage an installed base of 7.4 billion smartphone users worldwide, beacon technology provides the key enabler for a growing array of lucrative applications.

Beacon operation

For all their potential, beacon devices are simple in concept, designed to transmit small amounts of information over ranges as short as a few centimeters or as long as several hundred meters. Beacons intended for micro-location applications need little more than a wireless transmitter, some nonvolatile storage for a unique ID, and an MCU to handle the communications protocol. Beacons designed to transmit ambient data such as temperature or humidity only need to add the appropriate sensor and sensor data conversion capability — a requirement that can often be satisfied by the analog peripherals already integrated in many MCUs used in these designs.

Beacons can operate in multiple roles in wireless applications. Broadcast beacons are designed with radio transmitters only, intended to transmit a small amount of information for reception by any compatible host. For example, broadcast beacons designed to help airline passengers find their gate would periodically transmit a unique ID. In turn, a smartphone app would use this information to place the user with great accuracy within the airline terminal.

Beacons designed to engage in two-way communications serve as peripheral devices intended to provide information to a host or as central devices intended to collect information from peripheral devices. In a typical beacon application, peripheral beacons interact with a host such as a smartphone or other communications hub. For example, a peripheral beacon in a heart-rate monitor might interact with a host to mutually authenticate the exchange of the user’s health data or to perform over-the-air updates of beacon firmware as the need arises.

Beacon technology relies on Bluetooth Low Energy (BLE), which not only leverages the Bluetooth capability built into nearly every mobile product but also exhibits very low-power requirements during radio operations. In fact, BLE remains one of the most efficient short-range radio communications technologies: it consumes about 0.153 μW/bit — a fraction of that required in another popular short-range radio technology, ZigBee, which requires about 185.9 μW/bit (see the TechZone article "Comparing Low-Power Wireless Technologies"). Furthermore, in practice, BLE devices are typically in sleep mode for the majority of the time (Figure 2). Actual connection times last only a few milliseconds, so overall power requirements remain remarkably low.

Figure 2: BLE beacons spend most of their operational time in sleep mode, waking briefly to broadcast information or connect to a host for bidirectional communication — resulting in reduced overall power requirements for these designs. (Courtesy of Texas Instruments)

In building beacon devices, designers can take advantage of an increasingly rich array of integrated solutions designed to meet functional requirements while achieving very-low power consumption. BLE system-on-chip (SoC) devices such as STMicroelectronics BLUENRG-MSCSP, Nordic Semiconductor NRF51822, and Texas Instruments CC2541 combine low-power processor cores with on-chip BLE radios to simplify beacon design. As with other devices in this class, each of these BLE SoCs offer power-efficient radio operations as well as low-power modes that bring power consumption down to one or two microamps during sleep states.

Ambient power

With the availability of these ultra-low-power BLE SoCs, engineers can design beacons able to operate for months using a small battery such as the CR2032. Still, large-scale micro location applications can require placement of dozens or even hundreds of these devices to provide highly accurate location data. Consequently, the ability to achieve much longer maintenance-free operation is an advantage to organizations looking to place beacons once and not worry about downstream maintenance and associated costs.

With their low-power requirements, beacons are ideal candidates for use of energy-harvesting techniques. In fact, because beacons are typically placed in highly trafficked, well-lit locations, engineers can build beacon devices designed to operate solely from energy harvested from indoor lighting. For these applications, engineers can build an efficient ambient-powered beacon by combining an ultra-low-power BLE SoC such as the TI CC2541 with a specialized energy-harvesting power-management IC (PMIC) such as the TI BQ25505 (Figure3).

Figure 3: Thanks to their very low-power consumption, BLE SoCs such as the Texas Instruments CC2541 can operate from ambient power managed by specialized energy-harvesting ICs such as the TI BQ25505. (Courtesy of Texas Instruments)

Designed to extract energy from sources providing as little as a few microwatts of energy, the BQ25505 can manage all aspects of energy-harvesting power management including energy-transducer management, energy-storage management, and load management. For extracting power from indoor light sources, the BQ25505 and other devices in this class typically offer maximum-point power-tracking (MPPT) functionality designed to ensure that the solar cell efficiently extracts maximum power from available light. The device can save excess energy in a supercapacitor or rechargeable battery, managing the specific charge/discharge profiles required for specific types of energy-storage devices. On the load side, the device can switch the power source between the ambient source and stored power.

Supercapacitors offer an effective energy-storage alternative to rechargeable batteries in many beacon applications. Unlike typical rechargeable batteries, supercapacitors store charge electrostatically. Because little or no reaction occurs between the electrodes and the electrolyte, supercapacitors can perform hundreds of thousands of charge and discharge cycles. Furthermore, while batteries exhibit little or no capacity below their working voltage threshold, supercapacitors offer capacity even at lower voltages. Consequently, supercapacitors offer advantages in extended lifetime and low-voltage operation that can be particularly important for beacon applications.

For controlling connections between power sources and the load, the TI BQ25505 PMIC — as with many devices in this class — includes on-chip gate drivers designed to operate external FET load switches used to disconnect the load from the energy source or to multiplex in different power sources in more complex designs. For a specific beacon design suggested in Figure 3, designers can use the BQ25505’s VB_SEC_ON signal to control such a load switch. In normal operation, the BQ25505’s VBAT_OK signal remains high while the battery output remains above usable levels.

Providing an inverted VBAT_OK signal, VB_SEC_ON can be used to drive the gate of the system-isolating FET. When voltage from the supercapacitor (in this case) falls below a threshold voltage, the BQ25505 turns off the load switch to disconnect the BLE SoC rather than allow it to operate in an undervoltage condition. Other than the addition of a suitable FET and associated passive components including simple antenna, this combination of an energy-harvesting BQ25505 PMIC and CC2541 BLE SoC can serve as the complete hardware complement required for an ambient-powered beacon solution.

In summary

Beacon applications are rapidly emerging as one of the first large-scale deployments in the Internet of Things (IoT). For beacon developers, growing market demand translates into a need for more rapid development of suitable beacon designs able to operate as transmit-only broadcast devices or peripheral devices able to send and receive wireless communications. While BLE SoCs offer a quick solution for beacon designs, the combination of these SoCs with specialized energy-harvesting ICs offers an effective approach for creating maintenance-free beacons able to operate for years without batteries.

For more information about the parts discussed in this article, use the links provided to access product pages on the DigiKey website.