Discover the latest in wireless technology with our e-magazine, covering RTOS applications, selecting the right ESP32 Wi-Fi/Bluetooth module, and securing IoT connections to the cloud. Explore key application layer protocols for M2M and IoT functionality to enhance connectivity and performance. Stay ahead in the evolving world of wireless innovation.
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Wireless Modules I Volume 8
Real-Time Operating Systems (RTOS) and their applications How to select and use the right ESP32 Wi-Fi/ Bluetooth module IoT security fundamentals: connecting securely to IoT Cloud services Application layer protocol options for M2M and IoT functionality
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Editor’s note In the dynamic world of technology, wireless communication stands as a cornerstone of modern innovation, reshaping how we interact with our surroundings and with each other. Wireless technology, at its core, is the transmission of information over a distance without the need for wires, cables, or any other physical connection. This seemingly simple concept has revolutionized communication, enabling not just cell phone calls and text messages, but also the rapid expansion of the Internet, media streaming, and much more. The impact of wireless technology extends beyond personal communication, deeply embedding itself in various sectors such as healthcare, automotive, and the burgeoning field of the Internet of Things (IoT). The future trajectory of wireless technology is towards faster, more reliable, and more pervasive networks. The ongoing rollout of 5G technology promises not only higher data rates and reduced latency but also the ability to connect a massive number of devices simultaneously. This leap forward presents engineers with both opportunities and challenges, requiring innovative solutions in network infrastructure, signal processing, and application development. Wireless technology is a dynamic and ever- evolving field that demands a multidisciplinary approach from engineers. Its profound impact on various sectors makes it an exciting area for engineering exploration and innovation. As we move forward, the role of engineers will be pivotal in shaping the future of wireless communication, ensuring its growth, efficiency, and security.
4 Real-Time Operating Systems (RTOS) and their applications 8 Use a cellular and GPS SiP to implement asset tracking for agriculture and smart cities 18 How to select and use the right ESP32 Wi-Fi/Bluetooth module 24 IoT security fundamentals: connecting securely to IoT Cloud services 32 Special feature: retroelectro The ALOHA System: Task II 40 Application layer protocol options for M2M and IoT functionality 46 Deploy a secure Cloud-connected IoT device network complete with Edge computing capabilities 54 Use rugged multiband antennas to solve the mobile connectivity challenge 60 Getting started with Zephyr: a developer’s guide to your first project
For more information, please check out our website at www.digikey.com/automation.
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because tasks can be blocked to wait for availability of RTOS objects. Most RTOS have objects such as: ■ Message queue ■ First-in-first-out (FIFO) queue to pass data ■ Data can be sent by copy or by reference (pointer) ■ Used to send data between tasks or between interrupt and task
A Real-Time Operating System (RTOS) is a lightweight OS used to ease multitasking and task integration in resource and time constrained designs, which is normally the case in embedded systems. Besides, the term ‘real- time’ indicates predictability/ determinism in execution time rather than raw speed, hence an RTOS can usually be proven to satisfy hard real-time requirements due to its determinism.
Scheduler
Schedulers in RTOS control which task to run on the CPU, and different scheduling algorithms are available. Normally they are: ■ Pre-emptive – task execution can be interrupted if another task with higher priority is ready ■ Co-operative – task switch will only happen if the current running task yields itself Pre-emptive scheduling allows higher priority tasks to interrupt a lower task in order to fulfil real-time constraints, but it comes in the cost of more overhead in context switching. Inter-task communication (ITC) Multiple tasks will normally need to share information or events with each other. The simplest way to share is to directly read/write shared global variables in RAM, but this is undesirable due to risk of data corruption caused by a race condition. A better way is to read/ write file-scoped static variables accessible by setter and getter functions, and race conditions can be prevented by disabling interrupts or using a mutual exclusion object (mutex) inside the setter/getter function. The cleaner way is using thread-safe RTOS objects like message queue to pass information between tasks. Besides sharing of information, RTOS objects are also able to synchronize task execution
Semaphore ■ Can be treated as a reference counter to record availability of a particular resource ■ Can be a binary or counting semaphore ■ Used to guard usage of resources or synchronize task execution Mutex ■ Similar to binary semaphore, generally used to guard usage of a single resource (MUTual EXclusion) ■ FreeRTOS mutex comes with a priority inheritance mechanism to avoid priority inversion (condition when high priority task ends up waiting for lower priority task) problem Mailbox ■ Simple storage location to share a single variable ■ Can be considered as a single element queue Event Group ■ Group of conditions (availability of semaphore, queue, event flag, etc.) ■ Task can be blocked and can wait for a specific
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Key concepts of RTOS are:
Task
Tasks (could also be called processes/threads) are independent functions running in infinite loops, usually each responsible for one feature. Tasks are running independently in their own time (temporal isolation) and memory stack (spatial isolation). Spatial isolation between tasks can be guaranteed with the use of a hardware memory protection unit (MPU), which restricts accessible memory region and triggers fault exceptions on access violation. Normally, internal peripherals are memory-mapped, so an MPU can be used to restrict access to peripherals as well. Tasks can be in different states: ■ Blocked – task is waiting for an event (e.g., delay timeout, availability of data/resources) ■ Ready – task is ready to run on CPU but not running because CPU is in use by another task ■ Running – task is assigned to be running on CPU
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Real-Time Operating Systems (RTOS) and their applications Written by:
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Lim Jia Zhi, Senior Embedded Software Engineer at DigiKey
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Real-Time Operating Systems (RTOS) and their applications
interrupt handling is a technique of deferring interrupt computation into an RTOS task, the ISR will only generate an event through the RTOS object, then the RTOS task will be unblocked by the event and do the computation.
Low Energy (BLE) beacon, the MCU can be put into deep sleep between the advertising interval. As shown in Figure 1, the beacon is put into deep sleep mode for most of the time, consuming power in tens of µA. Conclusion An RTOS provides features like scheduler, tasks, and inter-task communication RTOS objects, as well as communication stacks and drivers. It allows developers to focus on the application layer of the embedded software, and design multitasking software with ease and speed. However, just like any other tools, it has to be used properly in order to bring out more value. To create safe, secure, and efficient embedded software, developers should know when to use RTOS features and also how to configure RTOS.
(e.g., from mutex to counting semaphore) if there is more than one SPI module available. OSAL and other abstraction layers help in software testing as well by simplifying mock function insertion during unit testing. Tick interval selection Ideally, a lower tick rate is better because of less overhead. To select a suitable tick rate, the developer can list down timing constraints of modules in an application (repeating interval, timeout duration, etc.). If there are some outlier modules needing a small interval, having a dedicated timer interrupt can be considered for the outlier modules rather than increasing RTOS tick rate. If the high frequency function is very short (e.g., write to register to turn an LED on/off), it can be done inside an Interrupt Service Routine (ISR), otherwise deferred interrupt handling can be used. Deferred
on a different RTOS. Similar design patterns allow us to develop applications on different microcontrollers and even a different RTOS. Modularity Divide and conquer. By separating features in different tasks, new features can be added easily without breaking other features, provided that the new feature does not overload shared resources like the CPU and peripherals. Development without RTOS will normally be in a big infinite loop where all features are part of the loop. A change to any feature within the loop will have an impact on other features, making the software hard to modify and maintain. Communication stacks and drivers Many extra drivers or stacks like TCP/IP, USB, BLE stacks, and graphics libraries are developed/ ported for/to existing RTOSs. An application developer can focus on an application layer of the software and reduce time to market significantly.
that a RTOS object can be created successfully, saving the hassle of handling a possible failed allocation and making the application more deterministic. In terms of deciding stack size needed for a task, the task can be run with a bigger (more than enough) stack size and then the stack usage can be checked in runtime to determine the high- water mark. There is a static stack analysis tool available as well. Operating system abstraction layer (OSAL) and meaningful abstraction Just like Hardware Abstraction Layer (HAL), use of the RTOS abstraction layer allows application software to migrate easily to other RTOSs. Features of RTOSs are quite similar, so creating OSAL should not be too complicated. For example: Using the freeRTOS API directly: if( xSemaphoreTake( spiMutex, ( TickType_t ) 10 ) == pdTRUE ) { // dosomething } Wrapping the RTOS API into OSAL: if( osalSemTake( spiMutex, 10 ) == true) { //dosomething } Using the abstraction layer on inter- task communication to make code more readable and minimize the scope of an RTOS object: if( isSpiReadyWithinMs( 10 ) ) { // doSomething } Additionally, the abstraction also allows a programmer to change the RTOS object used underneath
combination condition to be fulfilled ■ Available in Zephyr as a Polling API, in FreeRTOS as QueueSets
System tick
Tick suppression for low power application
RTOS need a time base to measure time, normally in the form of a system tick counter variable incremented in a periodic hardware timer interrupt. With system tick, an application can maintain more than time-based services (task executing interval, wait timeout, time slicing) using just a single hardware timer. However, a higher tick rate will only increase the RTOS time base resolution, it will not make the software run faster.
Tickless idle disables tick interrupt when the system is going idle for a longer time. One significant way for embedded firmware to reduce power consumption is to put the system in low power mode for as long as possible. Tickless idle is implemented by disabling the periodic tick interrupt and then setting up a countdown timer to interrupt when a blocked task is due to execute. If there is no task waiting for a timeout, the tick interrupt can be disabled indefinitely until another interrupt occurs (e.g., button pressed). For example, in the case of a Bluetooth
Why use RTOS?
Organization Applications can always be
written in a bare metal way, but as the code complexity increases, having some kind of structure will help in managing different parts of the application, keeping them separated. Moreover, with a structured way of development and familiar design language, a new team member can understand the code and start contributing faster. RFCOM Technologies has developed applications using different microcontrollers like Texas Instruments’ Hercules, Renesas’ RL78 and RX, and STMicroelectronics’ STM32
Figure 1: Current consumption of a BLE beacon Credit: RFCOM
Tips Static allocation
Use of static allocation of memory for RTOS objects means reserving memory stack in RAM for each
RTOS object during compile time. An example of a static
allocation function in freeRTOS is xTaskCreateStatic(). This ensures
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and design requirements of asset tracking. It then introduces a GPS and cellular narrowband system- in-package (SiP) solution from Nordic Semiconductor and shows how it can greatly simplify the implementation of GPS-enabled cellular devices for asset tracking and other agriculture and smart city IoT applications. Why asset tracking is increasingly important The ability to ship products efficiently is vital to commerce: Amazon alone shipped an estimated five billion packages in 2019, spending almost $38 billion in shipping costs – a 37% increase over 2018. For any shipping company, delays, damage, and theft place a significant strain on manufacturers, distributors, and customers. For Amazon, nearly a quarter of those shipped packages were returned, 21% because the customer received a damaged package. Amazon is by no means alone in allocating a significant portion of their budget to shipping. According to the 2020 State of Logistics report from the Council of Supply Chain Management Professionals (CSCMP), companies spent nearly
Developers of Internet of Things (IoT) and asset tracking devices and systems for industry, agriculture, and smart cities need a way to communicate over long distances at minimal power for extended periods of time. Wireless technologies such as RFID tags, Bluetooth, and Wi-Fi are already widely used for asset tracking solutions, but they have limited range and consume too much power. What’s required is a combination of GPS and an adaptation of infrastructure such as cellular networks that are already widely deployed and are designed for communications at longer ranges than available with Wi-Fi or Bluetooth. LTE-based cellular networks were originally designed for wide bandwidth wireless connectivity for mobile products and devices. IoT applications, on the other hand, can get by using lower power, narrowband cellular technologies such as long-term evolution for machines (LTE-M) and Narrowband IoT (NB-IoT). Still, RF/wireless design is difficult, and developers lacking extensive experience, particularly with respect to cellular, face great difficulty implementing a functioning design that optimizes wireless performance and power consumption, while also meeting international regulatory guidelines for both cellular and GPS location services, as well as specific carrier requirements.
Use a cellular and GPS SiP to implement asset tracking for agriculture and smart cities
Written by: Stephen Evanczuk Contributing Author at DigiKey
$1.7 trillion on shipping costs in 2019 – an expenditure that
accounts for 7.6% of the US gross national product (GDP). At these levels, the ability to track packages, identify delays and instances of
This article describes the trends
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damage can provide significant benefit to suppliers and purchasers to correct shipment problems. Besides following packages through the supply chain, most enterprises need improved methods for tracking their own assets and locating misplaced items. Yet, half of all businesses still manually log assets, and of those, many rely on employees to search through warehouses, plants, and physical locations to find missing assets. Comparing connectivity technologies for asset tracking Although a number of solutions have emerged to help automate asset tracking, the underlying technologies have limited coverage area, are expensive per unit cost, or have high power requirements. The latter is critical as asset tracking and remote IoT devices are battery- powered devices. Conventional tracking methods based on passive radio frequency identification (RFID) cannot provide live data in transit and require packages to pass through some physical checkpoint to detect the RFID tag attached to a package. Battery-powered active RFID tags are able to provide real-time location data but require additional infrastructure and remain limited in coverage.
Alternatives based on low-power ultra-wideband (UWB) technologies can achieve significant range, but network coverage remains limited. In fact, few alternatives can provide the kind of global coverage already available with low-power wide-area network (LPWAN) cellular solutions based on LPWAN technology standards defined by 3rd Generation Partnership Project (3GPP) – the international consortium that defines mobile communications standards. Achieving global reach with cellular connectivity Among 3GPP standards, those based on LTE-M and NB-IoT technologies are designed specifically to provide a relatively lightweight cellular protocol well matched to IoT requirements for data rate, bandwidth, and power consumption. Defined in 3GPP Release 13, LTE Cat M1 is an LTE-M standard that supports 1 megabit per second (Mbit/s) for both downlink and uplink transfers with 10 to 15 millisecond (ms) latency and 1.4 megahertz (MHz) bandwidth. Also defined in 3GPP Release 13, Cat-NB1 is an NB-IoT standard that offers 26 kilobits per second (Kbits/s) downlink and 66 Kbits/s uplink with 1.6 to 10 s latency and 180 kilohertz (kHz) bandwidth. Defined in 3GPP Release 14, another NB-IoT standard, Cat-NB2 offers higher date rates at 127
Kbits/s downlink and 159 Kbits/s uplink. Although the specific characteristics of these two broad classes of LPWAN technology lie well beyond the scope of this brief article, both can serve effectively for typical asset tracking applications. Combined with sensors and global positioning satellite (GPS) capabilities in compact packages, asset tracking solutions based on LTE-M or NB-IoT based cellular LPWANs can support the kind of capabilities required for asset management and end-to-end logistics. Given LPWAN’s potential for achieving greater efficiency and cost savings, cellular LPWAN continues to play a greater role in logistics. With the availability of the nRF9160 SiP from Nordic Semiconductor, developers can more quickly and easily serve the growing demand for LPWAN- based devices needed for more effective asset tracking or other IoT applications.
array (LGA) package. Along with an Arm Cortex-M33-based microcontroller dedicated to application processing, nRF91 SoC variants integrate an LTE-M modem in the NRF9160-SIAA SiP, NB-IoT modem in the NRF9160-SIBA SiP, and both LTE-M and NB-IoT as well as GPS in the NRF9160-SICA SiP. Furthermore, the nRF9160 SiP is pre-certified to meet global, regional and carrier cellular requirements, allowing developers to quickly implement cellular connectivity solutions without the delays typically associated with compliance testing. All SiP versions combine the microcontroller-based application processor and modem with an extensive set of peripherals, including a 12-bit analog-to-digital converter (ADC) often needed in sensor designs. The SiP further packages the SoC with an RF front- end, power management integrated circuit (PMIC), and additional components to create a drop-in solution for LPWAN connectivity (Figure 2). Serving as the host processor, the SoC’s microcontroller integrates a number of security capabilities designed to meet the growing demand for security in connected devices, including IoT devices and asset tracking systems. Building on the Arm TrustZone architecture, the microcontroller embeds an Arm Cryptocell security block, which combines a public key cryptography accelerator
Figure 1: Advanced direction-finding capabilities in Bluetooth support precision location of a tag in three-dimensional space. Image source: Nordic Semiconductor
low energy (BLE) and Wi-Fi offer progressively greater range within a coverage area equipped with fixed locators for each technology. Building on a rich ecosystem of devices and software, BLE and Wi-Fi are already applied in location-based applications such as COVID-19 contact tracing and conventional real-time location services (RTLS), respectively. With the availability of direction-finding features in Bluetooth 5.1, the location of a tag can be accurately calculated based on angle-of-arrival (AoA) and angle-of-departure (AoD) data (Figure 1). While BLE applications remain limited to short-range applications, Wi-Fi’s greater range can make it effective for use in asset tracking applications within a warehouse or enterprise campus. Yet, Wi-Fi RTLS tags are typically expensive devices
with power requirements that make batteries impractical, thereby limiting its use to tracking larger, expensive assets. At the same time, large-scale deployments using either of these technologies can suffer from increasing noise in their reception bandwidth, leading to lost or corrupted packets and degradation of location detection capabilities. Despite their potential use for tracking assets locally, neither RFID, BLE, nor Wi-Fi can provide the range of coverage needed to easily track an asset once it leaves the warehouse or enterprise campus. The ability to track a package or piece of equipment regionally or even globally depends on the availability of a wireless technology able to achieve both extended reach and low power operation.
How a SiP device can deliver a drop-in asset tracking solution
Nordic Semiconductor’s low-power nRF9160 SiP device combines a Nordic Semiconductor nRF91 system-on-chip (SoC) device with support circuitry to provide a complete LPWAN connectivity solution in a single 10 x 16 x 1.04 millimeter (mm) land grid
Compared to RFID tags, Bluetooth
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Developers can override the default low-power sub mode, switching instead to a constant latency sub mode. In constant latency sub mode, the PMU maintains power to some resources, trading an incremental increase in power consumption for the ability to provide a predictable response latency. Developers can invoke a third power mode using the external enable pin, which powers down the entire system. This capability would typically be used in a system design that uses the nRF9160 SiP as a communications coprocessor controlled by the host system’s main processor. These power optimization features enable the SiP to achieve the kind of low power operation needed to ensure extended battery life in an asset tracking device. For example, with the microcontroller in the idle state and the modem powered down, the SiP consumes only 2.2 microamps (μA) with the real-time counter active. With the microcontroller and modem both off and power maintained only to the general-purpose input output (GPIO)-based wakeup circuitry, the SiP consumes only 1.4 μA. The SiP continues to achieve low power operation while executing various processing loads. For example, running the CoreMark benchmark with a 64 MHz clock requires only about 2.2 milliamps (mA). Of course, as more peripherals are enabled, power consumption rises
accordingly. Still, many sensor- based monitoring applications can often operate effectively at reduced operating rates that help maintain low power operation. For example, current consumption for the integrated differential successive approximation register (SAR) ADC drops from 1288 mA to less than 298 mA when switching from a high accuracy clock to a low accuracy clock for sampling in either scenario at 16 kilosamples per second (Ksamples/s). The device also uses other power optimization features for its other functional blocks including GPS. In normal operating mode, continuous tracking with GPS consumes about 44.9 mA. By enabling a GPS power saving mode, current consumption for continuous tracking drops to 9.6 mA. By reducing the GPS sampling rate from continuous to every two minutes or so, developers can significantly reduce power. For example, the GPS module consumes only 2.5 mA when performing a single-shot GPS fix every two minutes. The device’s support for other power saving operating modes also extends to the nRF9160 SiP’s modem. With this device, developers can enable modem features supporting special cellular protocols designed specifically to reduce power in battery-powered connected devices.
Figure 2: The Nordic Semiconductor nRF9160 SiP combines an SoC with application processor and LTE modem with other components needed to implement a compact low power cellular-based design for asset tracking or other IoT applications. Image source: Nordic Semiconductor
How the nRF9160 SiP achieves low power cellular connectivity The nRF9160 SiP combines its extensive hardware functionality with a full set of power management features. Its included PMIC is supported by a power management unit (PMU) which monitors power usage and automatically starts and stops clocks and supply regulators to achieve the lowest possible power consumption (Figure 3). Along with a System OFF power mode, which maintains power only to circuits needed to wake the device, the PMU supports a pair of System ON power sub modes. After power-on-reset (POR), the device comes up in the low-power sub mode, which places functional blocks including the application processor, modem, and peripherals in an idle state. In this state, the PMU automatically starts and stops clocks and voltage regulators for different blocks as needed.
Utilizing low power cellular protocols As with any wireless device, the largest contributor to power consumption, besides the host processor, is typically the radio subsystem. Conventional cellular radio subsystems take advantage of power saving protocols built into the cellular standard. Smartphones and other mobile devices typically use a capability called discontinuous reception (DRX), which allows the device to turn off its radio receiver for a period of time supported by the carrier network. Similarly, the extended discontinuous reception (eDRX) protocol lets low power devices such as battery-operated asset trackers or other IoT devices specify how long they plan to sleep before checking back in with the network. By enabling eDRX operation, an LTE-M device can sleep up to about 43 minutes while an NB-IoT device can sleep up to about 174 minutes, dramatically extending battery life (Figure 4). Another cellular operating mode, called power save mode (PSM), enables devices to remain registered with the cellular network even while they are in sleep mode and unreachable by the network. Normally, if a cellular network is unable to reach a device within some period of time, it will terminate the connection with the device and require the device to
with mechanisms designed to protect sensitive data. In addition, a secure key management unit (KMU) provides secure storage for multiple types of secret data including key pairs, symmetric keys, hashes, and private data. A separate system protection unit (SPU) also provides secure access to memories, peripherals, device pins and other resources. In operation, the SoC’s microcontroller serves as the host, executing application software as well as starting and stopping the modem. Other than responding to start and stop commands from the host, the modem handles its own operations using its substantial complement of integrated blocks including a dedicated processor, RF transceiver, and modem baseband. Running its embedded
firmware, the modem fully supports 3GPP LTE release 13 Cat-M1 and Cat-NB1. Release 14 Cat-NB2 is supported in hardware but requires additional firmware to operate. Figure 3: The nRF9160 SiP includes a PMU that automatically controls clocks and supply regulators to optimize power consumption. Image source: Nordic Semiconductor
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additional parts beyond decoupling components, antennas, and those needed for separate matching networks for GPS and LTE antennas (Figure 6). Developers can easily combine the nRF9160 SiP with a Bluetooth device, such as Nordic Semiconductor’s NRF52840 Bluetooth wireless microcontroller and sensors, to implement a sophisticated sensor-based GPS enabled cellular asset tracker that provides users with access to data through their smartphones and other Bluetooth enabled mobile devices. Nordic Semiconductor further helps developers quickly begin evaluating cellular-based designs through a pair of development kits. For rapid prototyping of sensor- based asset tracking applications, the Nordic Semiconductor NRF6943 THINGY:91 cellular IoT development kit provides a complete battery-powered sensor
system that pairs the nRF9160 SiP with an NRF52840 Bluetooth device, multiple sensors, basic user interface components, a 1400 milliamp-hour (mAh) rechargeable battery, and a SIM card to allow out-of-the-box cellular connectivity (Figure 7). For custom development, the Nordic Semiconductor NRF9160- DK kit serves as an immediate development platform and reference for new designs. Although it does not include sensors like the THINGY:91, the NRF9160-DK kit combines an nRF9160 SiP with an NRF52840 Bluetooth device and includes a SIM card along with multiple connectors including a SEGGER J-Link debugger interface (Figure 8). For software development of an asset tracking application, Nordic includes a complete nRF9160 asset tracking application with its nRF Connect software development kit (SDK). The SDK combines Nordic’s nrfxlib software library for its SoCs, a Nordic fork of the Zephyr Project real-time operating system (RTOS) for resource constrained devices, and a Nordic fork of the MCUboot project secure bootloader. The THINGY:91 and NRF9160-DK kits come preloaded with the asset tracking application designed to connect with Nordic’s own nRF Cloud IoT platform. Using the preconfigured settings with either kit, developers can immediately
Figure 4: The nRF9160 SiP’s modem supports extended discontinuous reception which allows devices to achieve dramatic power savings by sleeping for a period of time negotiated with the cellular network. Image source: Nordic Semiconductor
eDRX
Figure 6: Using the Nordic Semiconductor nRF9160 SiP, developers need few additional components to
Up to 40- minutes vs. today’s upper limit of 2.56 seconds
implement the hardware design for a complete cellular-based asset tracker or other IoT device. Image source: Nordic Semiconductor
Sleep
Sleep
Time
power consumption. When in its unreachable stage with PSM, the device consumes only 2.7 μA. eDRX uses only slightly more current, consuming 18 μA in Cat-M1 operation or 37 μA in Cat-NB1 operation while using cycles of 82.91 seconds. Developing low power asset tracking solutions Implementing the hardware design for an asset tracking device based on the nRF9160 SiP requires few
execute a reattachment procedure that consumes an incremental amount of power. During long-term operation of a battery-powered device, this repeated small consumption of power can exhaust or significantly reduce battery charge. A device enables PSM by providing the network with a set of timer values that indicate when it will periodically become available and how long it will remain reachable before returning to sleep mode (Figure 5). Because of the PSM negotiation, the carrier network does not detach the device. In fact, the device can wake at any time and resume communications. The benefit is that it uses its low power sleep mode when it has nothing to communicate without losing its ability to wake as needed and instantly communicate. The nRF9160 SiP supports both eDRX and PSM, enabling the device to maintain operation with minimal
Figure 7: The Nordic Semiconductor NRF6943 THINGY:91 cellular IoT development kit provides a complete platform for rapidly prototyping sensor-based applications with both cellular and Bluetooth connectivity. Image source: Nordic Semiconductor
Figure 5: The cellular PSM protocol allows devices to take advantage of low power sleep modes without incurring the power costs of reattachment by negotiating specific periods when they are not reachable. Image source: Nordic Semiconductor
begin evaluating cellular-based asset tracking and prototyping their own applications. Along with the preloaded firmware, Nordic provides complete source code for the asset tracking application. By examining this code, developers can gain a deeper understanding of the NRF9160 SiP’s capabilities, and its use in supporting GPS localization and
LTE-M/NB-IoT connectivity in an asset tracking application. The main routine in this sample software illustrates basic design patterns for implementing a custom asset tracking application. When started, the main routine invokes a series of initialization routines. Among those routines,
PSM
Device not reachable
Time
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extend this software package to implement their own asset tracking applications or use its code examples to implement their own application architecture.
static void work_init(void) { k_work_init(&sensors_start_work, sensors_start_ work_fn); k_work_init(&send_gps_data_work, send_gps_ data_work_fn); k_work_init(&send_button_data_work, send_ button_data_work_fn); k_work_init(&send_modem_at_cmd_work, send_ modem_at_cmd_work_fn); k_delayed_work_init(&send_agps_request_work, send_agps_request); k_delayed_work_init(&long_press_button_work, long_press_handler); k_delayed_work_init(&Cloud_reboot_work, Cloud_ reboot_handler); k_delayed_work_init(&cycle_Cloud_connection_ work, cycle_Cloud_connection); k_delayed_work_init(&device_config_work, device_ config_send); k_delayed_work_init(&Cloud_connect_work, Cloud_ connect_work_fn); k_work_init(&device_status_work, device_status_ send); k_work_init(&motion_data_send_work, motion_ data_send); k_work_init(&no_sim_go_offline_work, no_sim_go_ offline); #if CONFIG_MODEM_INFO k_delayed_work_init(&rsrp_work, modem_rsrp_ data_send); #endif /* CONFIG_MODEM_INFO */ } Listing 2: The Nordic asset tracker sample application demonstrates the basic design pattern for transmitting data including sensor data as shown in this code snippet. Code source: Nordic Semiconductor
Listing 1: The Nordic asset tracker sample application builds on Zephyr RTOS utilities for queue management to create a series of queues with associated callback routines for handling various tasks such as sensor data acquisition and transmission to the Cloud. Code source: Nordic Semiconductor if (env_sensors_get_humidity(&env_data) == 0) { if (cloud_is_send_allowed(CLOUD_CHANNEL_ HUMID, env_data.value) && cloud_encode_env_sensors_data(&env_data, &msg) == 0) { err = cloud_send(cloud_backend, &msg); cloud_release_data(&msg); if (err) { goto error; } } } [code deleted] static void env_data_send(void) { [code deleted] if (env_sensors_get_temperature(&env_data) == 0) { if (cloud_is_send_allowed(CLOUD_CHANNEL_ TEMP, env_data.value) && cloud_encode_env_sensors_data(&env_data, &msg) == 0) { err = cloud_send(cloud_backend, &msg); cloud_release_data(&msg); if (err) { goto error; } } }
Conclusion
Using conventional methods, the ability to track valuable packages or locate high value assets across agricultural
or smart city environments has been limited to wireless technologies such as RFID tags, Bluetooth, and Wi-Fi. Designers need greater range and more accurate location information over longer periods of time. Low-power LTE cellular standards like LTE-M or NB-IoT combined with GPS can meet these requirements, but implementation can be challenging due to the difficulty and nuances of RF design. As shown, a Nordic Semiconductor SiP provides a near drop-in solution for long-range, low power asset tracking. Using this pre-certified SiP and its development kits, developers can quickly evaluate cellular connectivity, prototype cellular-based GPS enabled asset tracking applications, and build custom asset tracking devices that take full advantage of the extended range and low power requirements of LTE-M and NB-IoT cellular connectivity.
Figure 8: The Nordic Semiconductor NRF9160-DK kit offers a comprehensive development platform for implementation of custom cellular-based applications for asset tracking and other IoT solutions. Image source: Nordic Semiconductor
one initialization routine configures the modem and establishes the LTE connection by sending a series of attention (AT) strings to define connection parameters and invoke the modem’s built-in functionality to connect to the carrier network. Another initialization routine, work_init, initializes a set of Zephyr RTOS work queues including those for sensor, GPS, and development board buttons (Listing 1). During this initialization phase, the functions associated with each work queue initialization invocation perform their own specific initialization tasks, including those required to perform any required updates. For example, the
sensors_start_work_fn function called by work_init sets up a polling mechanism that can periodically invoke a function, env_data_send, that sends sensor data to the Cloud (Listing 2). When running the asset tracker sample application on the Nordic Semiconductor NRF6943 THINGY:91 cellular IoT development kit, the application sends actual data from the THINGY:91’s onboard sensors. When running on the Nordic Semiconductor NRF9160- DK development kit, it sends simulated data using a sensor simulator routine included in the SDK. Developers can easily
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wireless design. As a low-cost Wi-Fi/Bluetooth combo radio, it has gained popularity not just among hobbyists but also among IoT developers. Its low energy consumption, multiple open-source development environments, and libraries makes it perfectly suited for developers of all sorts. However, ESP32 comes in so many different modules and development boards that it can be difficult to select the right one.
Figure 1. The ESP32- WROOM-32D module runs at speeds up to 240 MHz and contains 8 Mbytes of onboard SPI flash. Credit: Espressif Systems
How to select and use the right ESP32 Wi-Fi/ Bluetooth module
Written by: Jacob Beningo Contributing Author at DigiKey
As the industrial automation accelerates, engineers on the factory floor are working to connect systems to an IoT that has in many ways left older factory floors behind. However, for both new and legacy systems, wireless connectivity to the IoT using Wi- Fi or Bluetooth has been made relatively simple using ESP32 modules and kits. Created and developed by Espressif Systems, ESP32 – a series of low- cost, low-power system-on-a-chip microcontrollers with integrated Wi- Fi and dual-mode Bluetooth – is a
This article introduces ESP32 solutions and shows how
developers can identify the right module and development board to start connecting their application to the IoT.
The ESP32 module
The ESP32 module is an all-in-one, integrated and certified Wi-Fi/ Bluetooth solution that provides not just the wireless radio but also an on-board processor with interfaces to connect with various
breakthrough for automation engineers who don’t want to get caught up in the nuances of radio frequency (RF) and Figure 2. The ESP32-WROOM- 32U is pin compatible with the WROOM-32D but replaces the latter’s on- board trace antenna with an IPEX connector for an external antenna, allowing for optimized RF characteristics. Credit: Espressif Systems
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Real-Time Operating Systems (RTOS) and their applications
For development of low-volume fixtures on the manufacturing floor, developers can use an ESP32 development board. These boards range from very basic ‘getting started’ boards to sophisticated boards that include secondary processors and LCDs. There are some that are also well suited for industrial automation applications, assuming simplicity of development is a key requirement. For instance, there’s the ESP32- DEVKITC-32D-F (Figure 3). This is a simple breakout board for the WROOM-32D that has all the power conditioning and programming circuits a designer or developer needs to get started. The board is powered either through an on- board USB micro connector or through the V-IN breakout header. Jumpers or wires can then be used to connect various components to the WROOM-32D. Another example is the Adafruit Industries Airlift ESP32 Shield. This not only includes the WROOM- 32D, but also has additional prototyping space (Figure 4). This prototyping space can be used to add connections to other shields in addition to adding custom circuitry. A developer could use this area to build input and output circuits for low voltage industrial automation applications. There is also an onboard SD card connector that makes developing a data logging application that much easier.
an external antenna that they can arrange within their product for optimal RF characteristics. An interesting point about the WROOM-32D modules is that they also come in various flash memory sizes. The modules come in additional memory support variants like the ESP32-WROOM-32D with 8 Mbytes and the ESP-WROOM-32D with 16 Mbytes. Selecting an ESP32 development board for industrial control The ESP32 modules are a great choice when designing a board that will be used in production or where they will be put on a board that will be used in ‘high’ volume.
Figure 5. The Digilent ESP32 PMOD board provides the ESP32 module in an easy to connect expansion format for use with other processors and development boards. Credit: Espressif Systems
Figure 3. TThe ESP32-DEVKITC-32D-F development board includes breakout headers for connecting to any of the WROOM-32D pins and can be powered through USB for development purposes. Credit: Espressif Systems
peripherals. The processor actually has two processing cores whose operating frequencies can be independently controlled between 80 megahertz (MHz) and 240 MHz. The processor’s peripherals make it easy to connect to a range of external interfaces such as:
additional hardware and layout complexity associated with an IPEX connected antenna. However, if the IPEX connector option is selected, there are plenty of good antenna options, such as Inventek Systems’ W24P-U.
automation applications where a development board with an additional processor is being used and the ESP32 will just be providing connectivity rather than handling the whole application load. In these applications, the development board or product may have expansion PMOD connectors onboard. Rather than custom designing a PMOD board for the ESP32, developers can leverage the Digilent ESP32 PMOD breakout board (Figure 5). The ESP32 PMOD provides a PMOD standard connector along with the following:
■ Four pin I/O expansion ■ Jumpers for boot configuration The Espressif Systems ESP- WROVER-KIT provides a full ESP32 development solution with everything designers need to develop an ESP32-based application (Figure 6). For example, the WROVER includes an FT2232HL USB to serial converter from FTDI which makes it easy to program the ESP32 module without the need for custom programming tools. The board also includes an onboard 3.2 inch LCD, a microSD connector, an RGB LED and a camera interface. The development board also as all the I/O lined up and made easily accessible through pin headers.
The module contains 4 megabytes (Mbytes) of flash and has 38 pins that are arranged to minimize the module’s size, making it nearly square. In fact, the WROOM- 32D is completely pin compatible with the ESP- WROOM-32U (Figure 2). The WROOM-32U replaces the onboard PC board trace antenna with an IPEX connector, based on the Hirose U.FL design. In doing so, the WROOM-32U saves board space and allows developers to connect
■ SPI ■ I2C ■ UART ■ I2S
■ Ethernet ■ SD Cards ■ Capacitive touch
There are several different ESP32 modules that a developer can select based on their application needs. The first and most popular ESP32 module is the ESP32- WROOM-32D, which runs at up to 240 MHz (Figure 1). The module includes a PC board trace antenna, which simplifies implementation. It also avoids having to add the
Figure 4. The Adafruit Airlift ESP32 Shield allows designers to prototype their design or build one-off circuits that can be used in industrial automation applications. The Airlift includes prototyping space that can be used for dedicated circuitry. Credit: Espressif Systems
■ A power LED indicator ■ An on-board user button
There may be some industrial
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Real-Time Operating Systems (RTOS) and their applications
■ Users that don’t have embedded programming experience should ‘flash’ MicroPython onto the ESP32 so that the application code can be written in the easy to learn Python scripting language ■ For the application, search the Internet for ESP32 examples and libraries to accelerate application development and integration (there are a lot of great examples already available) ■ In the design, make sure that the boot strapping pins are able to be used to boot into the update mode. This will make it very easy to update firmware in the field ■ Developers that follow these ‘tips and tricks’ will find that they can save quite a bit of time and grief when working with ESP32 for the first time.
using MicroPython.
experienced embedded software developers. The toolchain includes several useful pieces such as an IDE to develop the application, a compiler, libraries, and examples. The IDF uses FreeRTOS as the base real-time operating system (RTOS) along with the lwIP TCP/IP stack and TLS 1.2 for Wi-Fi. For developers who have minimal programming experience, the popular Arduino IDE can also be used to develop an application and deploy it to the ESP32. While the Arduino IDE is a bit slower and clunkier than a professional development environment, it offers a lot of examples and support for the ESP32, which can make development for a newbie much easier.
Finally, for developers who are interested in developing their application in Python, the ESP32 is supported by the open source MicroPython kernel. Developers can load MicroPython onto the ESP32 and then develop Python scripts for their application. This can make it very easy to update the application on-the-fly in an industrial setting and remove layers of required expertise that normally come with embedded development. Tips and tricks for working with ESP32 Getting started with ESP32 is not difficult, and a search of the web will provide detailed descriptions of how to set up the various software environments. That said, there are many nuances and decisions required of developers working with ESP32 for the first time. Here are a few ‘tips and tricks’ for getting started: ■ Carefully identify and configure a module’s boot pins – MTDI, GPIO0, GPIO2, MTDO and GPIO5 – to load an application from the correct memory source (internal flash, QSPI, Download, Enable/ Disable debug messages) ■ Set the serial output baud rate to the same baud rate as the ESP32 boot firmware baud rate. This will allow monitoring of the ESP32 boot messages, and the application debug messages, without reconfiguring the baud rate
ESP32 – a series of low-cost, low-power system-on-a-chip microcontrollers with integrated Wi-Fi and dual-mode Bluetooth – is a breakthrough for automation engineers who don’t want to get caught up in the nuances of radio frequency (RF) and wireless design.
All told, ESP32 is an excellent choice for connecting industrial automation equipment quickly and efficiently.
that there are several different development environments to choose from to develop and program the device. The most popular development tools include: ■ The Espressif IoT Development Framework (IDF)
Once a designer has decided which module and development board best fit their application, they need to spend some time looking at the development environment for the ESP32 that best fits their needs.
■ Arduino IDE ■ MicroPython
Selecting an ESP32 development environment
The first environment, the Espressif IDF, is a development toolchain for
The ESP32 has become so popular
E2PROM
32.768KHz crystal
Conclusion
12MHz
As shown, ESP32 has several different modules and development boards that developers can leverage to begin designing their industrial IoT application. The advantage of using ESP32 for this purpose is that it simplifies development by removing the need to understand RF circuitry and to certify the wireless receiver. ESP32 is also widely supported, not just by the module manufacturer but also within professional and hobbyist circles. Developers who are not familiar with embedded software can easily use the Arduino IDE or program their wireless application
I/O expand
JTAG
ChannelA
JTAG
LCD: 3.2 inch
D+/D-
USB Connector
FT2232HL
ESP32_Module
Camera
UART
ChannelB
UART
MicroSD
RGB LED
USB_5V
+3.3V
LDO: +5V->+3.3V
EXT_5V
Key1
Key2
Figure 6. The Espressif ESP-WROVER-KIT board provides industrial automation developers with an ESP32 module that has access to an RGB LED, microSD slot, camera, an LCD, and easily accessible I/O expansion. Credit: Espressif Systems
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Figure 1. As with other Cloud providers, AWS provides developers with a set of specialized services designed to enhance the security and effectiveness of transactions between IoT devices and enterprise Cloud services. Credit: Amazon Web Services
AWS IoT
IoT security fundamentals: connecting securely to IoT Cloud services
Using preconfigured development boards, developers can quickly gain experience with the security methods used by leading IoT Cloud services to authenticate connections and authorize use of IoT devices and Cloud resources. This article describes the connection requirements of two leading Cloud services, Amazon Web Services (AWS) and Microsoft Azure, and shows how developers can use development kits and associated software from a variety of vendors to quickly connect with these services.
Internet of Things (IoT) security depends on multiple layers of protection extending from the IoT device’s hardware foundation through its execution environment. Threats remain for any connected device, however, and typical IoT application requirements for Cloud connectivity can leave both IoT device and Cloud services open to new attacks. To mitigate these threats, IoT Cloud providers use specific security protocols and policies which, if misused, can leave IoT applications vulnerable.
Contributed By: Stephan Evanczuk, Contributing Author at Digikey
interact with each provider’s full set of Cloud resources such as virtual machines (VMs) and software- as-a-service (SaaS) offerings. Using a functionally similar set of mechanisms and capabilities, Azure IoT Hub and AWS IoT provide this portal for their respective enterprise Cloud offerings. At a minimum, these and other IoT portals use specific authentication protocols implemented through each provider’s software development kit (SDK) to create a secure connection. For AWS,
for both IoT devices and Cloud resources, Cloud services require the use of specific security protocols for mutual authentication of identity for sign in and subsequent authorization to ensure permitted usage of services. These protocols are typically included in a set of services that provide a secure portal between IoT devices and Cloud resources. As with other available IoT Cloud service platforms, AWS, and Azure each provide a specific entry portal that IoT devices need to use to
The role of IoT portals in Cloud services When an IoT device connects to a resource such as a Cloud service or remote host, it potentially exposes itself – and by extension the entire IoT network – to threats masquerading as legitimate services or servers. Conversely, the Cloud service itself similarly faces the threat of attacks from hackers mimicking IoT device transactions in an attempt to penetrate Cloud defenses. To help ensure protection
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