ST is celebrating the launch of the STM32WL3 and, with it, a comprehensive ecosystem of STM32Cube solutions. The STM32WL3 is a sub-GHz wireless microcontroller with a new ultra-low-power radio and an updated S2-LP transceiver featuring additional modulation support. Hence, beyond opening the door to more cost-effective bills of materials for products like smart meters and asset trackers, among many others, it symbolizes a new era as the sub-GHz device brings the S2-LP to the STM32Cube ecosystem. Developers can, therefore, expect a more straightforward path from the proof-of-concept to their final design thanks to hardware features targeting their applications, like the LC Sensor Controller and a familiar software ecosystem.
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What’s new?
Avid readers will remember that we announced the OEM launch of the STM32WL3 a year ago. Since then, our teams worked to create an ecosystem that would enable engineers to move from proof-of-concept to a final product rapidly. For instance, the STM32CubeWL3 firmware package comes with a hardware abstraction layer, middleware, and RTOS necessary to start writing applications in minutes. There are even application examples to get started faster. Moreover, tools like STM32CubeMX, STM32CubeProgrammer, STM32CubeMonitor, and STM32CubeIDE will receive updates over the coming months to support the new package and device, thus truly integrating the STM32WL3 into the STM32 ecosystem.
This announcement is highly symbolic because it fulfills the promise ST made when we released the STM32WL3 to OEMs. Furthermore, we are also taking this opportunity to launch new tools to optimize further the workflow of engineers working on our newest device. One of them is WiSE-RadioExplorer, a wide survey explorer with a graphical user interface to tweak the sub-GHz radio more easily and experiment with its capabilities. The other is WiSE-RadioCodeGen, which builds flowcharts that map actions the radio will take under certain conditions, thanks to a sequencer driver, thus giving developers vastly more granular control over the STM32WL3’s behavior.
The best way to get started is to grab one of the two Nucleo boards featuring the new device, the NUCLEO-WL3CC1 (high band) or NUCLEO-WL33CC2 (low band). They will help engineers run demo applications, test the new software utilities, and even provide layout inspiration since their schematics and bills of materials are free. ST is also launching the MLPF-WL-01D3/02D3/04D3, integrated power devices containing filters compatible with the STM32WL3, so integrators don’t even have to worry about what components to select or how to tune them, making the overall design phase even more intuitive. We are also providing a pre-certified and tuned reference design, the STDES-WL3xxxx.
From STM32WL5 to STM32WL3: Finding a new balance of power
The STM32WL entered volume production at the end of 2023. We worked with select partners and customers on the Nucleo platforms available today to make sure we could have a mass market launch today. It also enabled some of them to create unique designs. For instance, Lierda announced its WB18 module. Based on the STM32WL3, the WB18 simplifies data transfer within a network by using a serial interface for packet transmission, thus enabling point-to-point and point-to-multiple communication. The company also provides an LCD driver port for more interactive UIs. Similarly, SilentSmart launched its WS8561xLS, an STM32WL33 UART module targeting smart cities, smart homes, and niche applications like healthcare and industrial settings.
How did it start?
Launched in 2020, the STM32WL series showcased the first microcontroller with an embedded LoRa® transceiver, the STM32WLEx. Both the radio and the application ran on a Cortex-M4, enabling newcomers to enjoy a processor with enough computational throughput for a lot of mainstream applications while keeping costs down. Strengthened by the positive industry reception to this new type of device, ST released the STM32WL5 a year later. The MCU distinguished itself with a dual-core architecture that added a Cortex-M0+ to run the wireless stack on top of the Cortex-M4 of the earlier model. The device targeted more high-end applications that require the security and isolation that the Cortex-M0+ affords.
How is it going?
The STM32WL3 continues to expand the existing portfolio by targeting a new type of application: low-power and cost-sensitive systems. The new device, therefore, features a Cortex-M0+ for the radio and the application. Consequently, it offers a significantly lower power consumption with only 47 µA/MHz in dynamic consumption for the STM32WL3 versus 72 µA/MHz for the STM32WLE. The new MCU also has up to 256 kB of flash and up to 32 kB of RAM. Hence, when companies build a smart smoke detector or an asset tracker that will use a coin battery for years, they can benefit from the MCU’s energy efficiency while enjoying the necessary resources to run an application comfortably.
From S2-LP to 2 new radios: Reaching new optimization levels
Why have a wake-up radio?
Another innovation unique to the STM32WL3 is the presence of two radios, one dedicated to a low-power wake-up function. Designed for proximity detection, it only supports OOK modulation, has a continuous RX mode, and is compatible with a wide frequency band from 100 MHz to 2.4 GHz. As a result, it consumes a meager 4.2 µA, an order of magnitude lower than a traditional radio. For comparison, the regular sub-GHz module of the STM32WL3 needs 5.6 mA in RX mode, which is already considered an efficient device by today’s standards.
Developers can use a traditional gateway to take advantage of the wake-up radio. Many may already have one that’s supported since the wake-up radio covers a wide range of frequencies. When the STM32WL3 comes near the gateway, it receives a packet and triggers a wake-up function to turn the regular radio and MCU on. The wake-up radio is sensitive enough (-53 dBm) to have a range of tens of meters (more than 32 feet), which means it can operate in various settings, from warehouses to smart factories or smart cities. The output power also got a boost to reach up to +20 dBm in transmission, whereas the S2-LP reached +16 dBm.
Why improve on the S2-LP?
The regular radio in the STM32WL3 is an updated version of the S2-LP with support for (G)MSK, DBPSK, and DSSS on top of the traditional 4-(G)FSK, 2-(G)FSK, OOK, and ASK. Consequently, the device natively supports 802.15.4g and is compatible with 6LoWPAN, MBus, Sigfox, WiSUN, and KNX protocols. Moreover, thanks to its new capabilities, the STM32WL3 is Mioty-capable, thus further expanding the new device’s reach in Europe. The radio of the STM32WL3 is also more power efficient in RX (5.6 mA vs. 7 mA for the S2-LP) and TX (8 mA vs 10 mA for the S2-LP). It also provides greater output power at +20 dBm (+16 dBm for the S2-LP).
ST is also thrilled to announce that its partners are already working on wireless stacks to ensure developers can rapidly support these protocols. STACKFORCE already has a WMBUS/OMS stack ready to use for end nodes and gateways, and Fraunhofer IIS will have a Mioty stack ready by the first half of 2025. Additionally, a Wi-SUN PHY layer is also ready for certification, which should significantly reduce the time to market.
From flow metering to asset tracking: Solving new problems one app at a time
How to focus on smart metering?
To make the STM32WL3 even more meaningful, ST engineers added features tailored for some of the most popular use cases. For instance, the new device includes an LC Sensor Controller (LCSC), which detects mechanical-wheel fluid metering. For instance, as the wheel of a metering system tracks the amount of water consumed, a circuit inside the STM32WL3 increments a value inside a register after each wheel revolution. Consequently, the MCU records the wheel’s rotations without waking the Cortex-M0+ for more significant energy savings since it only requires between 2 µA and 4 µA. After the value stored in the register reaches a threshold or after a certain period, the system wakes the CPU, which records the value in memory.
Furthermore, ST is releasing a version of the STM32WL3 supporting a wireless band of 169 MHz. Ending with “A”, the STM32WL3 part number will thus be compatible with Wize, a European standard for remote areas that would benefit from long-range communication. The standard aims to popularize smart city applications, water metering, energy tracking, waste management, and more. ST is using the launch of the new STM32WL3 to contribute to this new interconnectivity effort at a very large scale.
How to optimize for worldwide asset tracking?
Another feature tailored for the most common applications is the presence of two power amplifiers for the sub-GHz radio. Indeed, since asset tracking is one of the widespread use cases for the STM32WL3, the device must be able to adapt to different regional wireless standards automatically. For instance, the European Union and Japan mandate using +14 dBm of output power, whereas North America goes up to +20 dBm. By having two power amplifiers, the STM32WL3 can automatically switch from one to the other. Engineers don’t have to qualify a different product for each region and can vastly simplify developments, which more than makes up for the cost associated with the presence of another amplifier.
How to streamline development?
Regarding developments, the STM32WL3 is symbolic because it brings the S2-LP DNA to the STM32 ecosystem. ST will continue to offer the S2-LP transceiver and support the existing software stacks to help teams that need a more modular approach. Put simply, many are still eyeing an S2-LP alongside an STM32 MCU for scalability or flexibility reasons. However, by the end of next year, the ability to use the STM32WL3 with the STM32Cube ecosystem will make it familiar and practical. In all cases, our goal is to ensure developers can write proofs-of-concept and demo applications much faster as the initialization process benefits from existing UIs, and example codes are often just a few clicks away.
