The real deployment phase of personal area network (PAN) has not yet arrived. We are at the breaking point of the new generation of wearable computers, sensors and peripherals, which will put our entanglement with the machine to a new level.
Traditionally, a PAN is associated with a wireless voice link, such as a Bluetooth connection to a wireless headset. Although this is a useful local machine-to-machine (M2M) personal link, it is far from reaching the practical potential that low power RF near-field technology PAN can provide.
This article will explore what options we have to generate and send data via our "personal electromagnetic bubble". This article will discuss the low-power levels and signal types used in various applications, ranging from wearable devices or simple "deep in-place" sensors to more complex high-definition video and image processing for real-time 3D gesture recognition.
We will discuss the standard chip-level solutions that are available today, such as IRDA, Wireless USB, Bluetooth, Z-Wave, ZigBee, and Wi-Fi, and study it from the perspective of bandwidth to determine what is expected to be visible and practical. The throughput. At the same time we will also discuss which standards are better for different functions. All parts, specifications, guides, and development tools referenced in this document can be found on the Digi-Key website.
Not all RF
Wireless links generally make us think of radio concepts, but not all wireless links are based on RF. Some line-of-sight, short-range, and low-bandwidth communications can be replaced with IR (infrared). For example, two-piece force feedback gloves for remote control of equipment or medical procedures. At this time, IRDA modules like ROHM RPM973-H11E2A do a better job (Figure 1). The transceiver is ultra-thin and self-contained, capable of providing optical link speeds of up to 4 Mbits/s without interference from ambient RF noise from any source. It also has a rugged structure that is suitable for harsh conditions.
Figure 1: Do not underestimate the usefulness of rugged IR as a line-of-sight link in moderate bandwidth data communications. There are a variety of well-designed, low-cost transceivers for engineers to choose from.
Although optical technology has its unique features, so far, the most widely used communication technology in emerging PAN applications is RF. Interestingly, low-cost, narrow-band AM, FM, ASK, FSK, carrier on/carrier off, and PSK type RF can be used for relatively short-range low-speed links. A computer mouse with a data rate of 1,200 bit/s works well.
The Murata TR3000 uses a 433.92 MHz carrier and ASK or OOK modulation, supporting data rates up to 115.2 Kbaud. Its working voltage is 2.7 to 3.7 V, and the current is only 3.8 mA when receiving data, and 7.5 mA current can be used for data transmission. Its energy consumption is even better. It can reduce the energy consumption of short-range links by an order of magnitude, thereby extending battery life (Figure 2).
Figure 2: Narrow-band transmissions Because of the relatively low data rate, lower power numbers can be used. However, noise sources and crowded interactive environments can cause problems.
Although power limitations can be applied to narrow-band AM and FM, there are too many possible sources of interference, so when an error occurs, such links generally do not undergo arbitration, collision detection, collision avoidance, and automatic retransmission. It is better to use a digital radio at this time.
Multiple digital standards are competing in the coveted larger PAN market, including consistent interoperable standards such as Bluetooth, USB, ZigBee, Wi-Fi, or Z-Wave.
With multiple IC-level devices coming on the market, Wireless USB will provide some assurance. The Cypress CYRF6936-40LTXC is the only part of the direct-sequence spread-spectrum wireless 2.4 GHz USB transceiver. Data speeds of 1.8 to 3.6 V devices are up to 1 Mbit/s, set and controlled using a 4 MHz SPI port. This is a 40-pin part with an exposed pad that is slightly larger than a narrowband solution. Its 34 mA emission (21.2 mA receive) current is also significantly higher. In fact, many applications are mostly dormant rather than awake, and can use a small battery to achieve long bursts of communication, especially if the battery can be charged.
Similar parts with an embedded controller are the Cypress CYRF89235-40LTXC, which offers an on-chip Harvard architecture M8C RISC processor up to 24 MHz and an emulation port (Figure 3). On-chip 32K flash memory can store stack and user code for certain applications. The 2 K RAM can be extended on the programmable I/O through an 8-bit port or through an I2C or SPI interface (both included).
Figure 3: The system-on-chip approach allows the embedded microprocessor to fully run the protocol stack while providing an embedded environment that can either store your application-specific code or build your own custom interface.
Not just voice
Bluetooth voice is most likely to dominate the headset field or for personal voice links in the future, although it uses far more power than it needs. For most parts, Bluetooth devices work together very well, even in crowded environments. The network sharing process makes the transceiver a simple type of query lock without having to maintain multiple sockets and complex protocol stacks.
On the other hand, Bluetooth low energy is ideally suited for non-voice applications such as sensors, actuators, and PANs. Similar to other standards, someone has already started to move forward with an integrated solution. One Bluetooth LE solution worth noting is CSR, its TCSR1010A05-IQQM-R single-chip Bluetooth LE SoC transceiver (Figure 4). As part of CSR's μEnergy Bluetooth low energy platform, the device also includes an embedded microcontroller. In this example, it is a 16-bit RISC processor running the BT LE stack, radio, interrupt, and external interface.
Figure 4: The embedded microprocessor can include not only digital radio peripheral functions, but also other connections and peripheral interfaces, including mixed signals.
It should be noted that these parts have more resources available. Both flash and RAM are 64 Kbytes in size. In addition, these parts also include a 10-bit A/D, 12 programmable I/O, SPI, I2C, UART, PWM, and a debug SPI port. With regard to radios currently under development, almost all have energy management features and can use 32 kHz real-time clock crystals to save more sleep power.
Another competitor in this area is STMicroelectronics, which offers the Bluetooth LE wireless network processor BLUENRGQTR. It also meets the Bluetooth v4.0 specification as a 1 Mbit/s compatible master and slave device. It can use 32 kHz clocks or oscillators to reduce power consumption or run at higher native frequencies for process-intensive data processing. In this case, the frequency is up to 32 MHz.
It is based on the ARM Cortex-M0 processor (Figure 5) with a 64K program flash and 12K SRAM. It also has SPI, I2C, UART, serial program and debug, and AES hardware. STMicroelectronics sees it as a potential peripheral controller in the PAN field and is particularly suitable for health care applications. The company also provides product training modules for Bluetooth LE health applications.
Figure 5: Not only 8-bit and 16-bit cores can be used in PAN applications, but the 32-bit Cortex-M0 can also operate on radio links and have tremendous processing power for your code.
Like many other vendors, STMicroelectronics also supports the stack and provides a development environment to help you speed development. In this example, the vendor's STEVAL-IDB002V1 is a useful demonstration and evaluation board for the BlueNRG low-power network processor.
Other possibilities
There are many obstacles that other wireless players have to overcome in order to get a share of the emerging PAN market in explosive growth. One example is ZigBee. This is a popular standard, supported by a number of device and module manufacturers, suitable for home and building automation applications.
Unlike Bluetooth, ZigBee does not have native support on smart phones, tablets, and laptops. This may have obstacles. ZigBee also needs a fairly complex stack, which means the cost of the node will be higher. ZigBee, on the other hand, has architectural arbitration and identification capabilities that have the advantage of being part of a larger mesh.
Wi-Fi is also an attractive place, especially in promoting the Internet of Things. It provides cloud-based connectivity and the chips and modules it provides are also certification-ready solutions. Although Wi-Fi has native support on smart phones, tablets, and laptops, it consumes too much power. The control flexibility may make it less suitable for PAN applications, so it may still not be a feasible solution, especially after it enters low-power mode every time, it needs to re-establish the connection when it wakes up, and the discovery mode also takes up a lot of Time and energy consumption.
There are other potential solutions. Z-Wave, ANT+, IOHomecontrol, W6LoPAN, and RF4CE are among application-specific and common protocols that are worth understanding.
All in all, we are witnessing the rapid development of a new generation of Internet-related products that will enhance our capabilities and our self-awareness. In this environment, smart phones are most likely to become the backbone of the personal area network, linking wearable devices such as health monitors, smart watches and display devices (such as Google glasses) and sensors embedded in various clothes and shoes. . This article explores the options engineers have to generate and receive data through personal "electromagnetic bubbles." We also discussed many possible protocols and reviewed representative parts.
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