Fast track to wireless connectivity with modules

Protocols such as Bluetooth’s low-power modes and LoRaWAN have made it possible to provide long-term connectivity for devices that rely on batteries even in locations that used to be considered impractical. For example, the low-power wide-area network (LPWAN) standards Sigfox and LoRaWAN make it possible for a sensor node to be as much as 50km from the nearest gateway unit.

This makes it possible to deploy sensors for use in farming, wildlife surveying and pipeline monitoring where the devices need to operate in remote regions. Coupled with efficient microcontrollers, the low-power wireless protocols can support situations where a device need have its battery recharged or replaced only after a matter of months or even longer, even when long-distance communications are involved.

The range of options for wireless connectivity continues to expand for both longer-range and local networks. Bluetooth, Thread, Zigbee and Z-Wave are among the many protocols available that suit applications for building and home monitoring as well as industrial automation. Recent entrants to the market for both local and longer-range use include Wirepas, which uses the same 2.4GHz spectrum as Bluetooth and WiFi, or the 1.9GHz DECT-2020 NR standard for longer-range transmissions.

The challenge of RF design

The issue for Original Equipment Manufacturers (OEMs) and integrators is dealing with the complexity and range of choices that wireless connectivity presents. Each protocol has its own characteristics that a development team must consider within the context of a larger board or module design.

Consider the contrast between Sigfox and LoRaWAN. The latter uses a spread-spectrum modulation scheme to avoid interference and can support data rates from 300bit/s to 50kbit/s. Sigfox on the other hand uses ultra-narrowband transmission for a lower data rate. LoRaWAN is designed to support bidirectional communication, while Sigfox is optimised for transfers from sensor nodes gateways and very low power consumption. As a result, the two protocols will suit different application architectures.

A number of the local-area standards use mesh technology to extend the range and capacity of the wireless infrastructure without increasing energy consumption. In a mesh environment, packets that cannot be sent directly to a gateway can be directed to it using short hops between nearby peers. However, there may be cases where the application is better suited to direct point-to-point models for latency or security reasons.

To determine how well a product will work in real-world applications, a development team may want to test different network options. They can then settle on a preferred wireless-connectivity solution with good evidence. If they choose to pursue the route of custom circuit and antenna design, this prototyping can take significant time. The development effort can be substantial in the case of RF: most wireless standards require the integration of multiple design skills.

They include knowledge of antenna structures and the effects they have on signal-to-noise ratios as well as the design of low-noise amplifiers and analogue mixers. An additional burden is the firmware needed for a host microcontroller to manage channel access and advanced functions such as mesh routing.

Antenna and front-end analogue design can be extremely difficult to handle if designers have limited experience of best practice. Small routing and layout changes can have dramatic effects on radio performance, which may translate into a loss of effective range and excessive power consumption.

With RF circuitry, a further issue for those pursuing custom designs is the need for testing and certification. Although testing for electromagnetic compatibility (EMC) is a requirement for all electronic products, the addition of RF interfaces complicates the process. Most legislation that covers RF transmissions puts stringent limits on power both within and outside the frequency bands used by the device.

Unexpected interactions between circuitry in the system can lead to devices failing these tests. An additional complication lies in the certification procedures that may be needed for specific protocols such as Bluetooth. To be deemed compatible, a device needs to demonstrate that it follows the specification and interoperates with products from other manufacturers.

Readymade RF modules to enable wireless connectivity

The added complications that accompany custom RF design make a strong argument for the use of readymade modules. The key advantage of an RF module is that it can be supplied in a form, often complete with antenna in the case of low-power protocols, that is fully tested and certified. The designers will have put together a board or package that is effectively self-contained, with some even containing the microcontroller and firmware that will be used to schedule transfers, which may be triggered using simple commands from a host processor. The result is a solution where integration to a host system does not have an impact on the RF module’s performance or its certification status.

There are many choices available, ranging from small integrated packages designed for size-constrained Internet of Things (IoT) sensor nodes to high-bandwidth board-level modules. There are a number of integration choices for module users.

Some modules use a simple parallel or serial interface that works in the same way as a serial communications channel, and which conforms to common expansion-board formats. An example is the STMicroelectronics STEVAL-IDB 008V2, a module compatible with the Arduino Shield format and which provides a full Bluetooth radio interface. Some, such as the STEVAL-IDB 0007V1M (pictured), have additional functionality in the form of integrated accelerometers and pressure sensors. Others employ protocols such as USB. For easy attachment to an evaluation board, Silicon Labs has implemented a Bluetooth 4.0 controller inside an USB-A connector with the BLED112-V1C.

Other modules are designed to be soldered directly to a carrier board for situations where the volume product needs to be as small as possible or to minimise connector costs. Murata, for example, has implemented some of the world’s smallest LPWAN modules in the form of chip-sized packages as well as designs targeted for Bluetooth and WiFi networks, such as the LBEE59B1LV-278. Similarly, Würth Elektronik, which is adding support for Wirepas to its portfolio, has developed several modules designed for soldering to a carrier. The company offers models such as the Proteus-III that delivers Bluetooth functionality and the WiFi-compatible Calypso. Another manufacturer specialising in chip-down modules for the Bluetooth and WiFi spaces is Taiyo Yuden.

Minimising potential IoT attacks

Modules can offer additional functions that ease the integration of wireless networking into the device firmware. An example is the WFI32E01 made by Microchip, which couples a certified WiFi transceiver design with a secure element that takes advantage of the company’s Trust&Go pre-provisioning service.

This provides the module with secure private keys that can be used to access cloud-computing services as soon as the device is plugged in. The provisioning avoids the need to have installation engineers configure the product before making a secure connection, minimising the potential for the attacks that are increasingly being brought against IoT devices.

Some manufacturers focus on ease of development for the software. Pycom specialises in modules that can run the MicroPython interpreter including the comprehensive development tools and libraries this can offer. This approach provides rapid applications prototyping for a range of wireless communications standards including local and LPWAN protocols.

As well as offering a wide range of products that extend beyond local and LPWAN products into cellular solutions, Laird can support the creation of test networks with its wireless gateways and sensors with integrated wireless connectivity. In addition, suppliers such as Laird can offer customisation for volume products and provide testing for customers who integrate the company’s wireless circuitry at the board and system level.

Through the use of modules, design teams can perform deep evaluations of the wireless protocols that are key to supporting IoT and other distributed-computing applications. Modules also enable a move to cost-effective volume production once design engineers have found the right combination of processing and communications for the job.