ST is celebrating the OEM launch of the STM32WL3, 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 will bring the S2-LP to the STM32Cube ecosystem by the end of 2024. 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.
The STM32WL has entered volume production, and we are starting to ship Nucleo platforms to select partners and customers. For instance, Lierda is announcing today 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 is launching its WS8561xLS, an STM32WL33 UART module targeting smart cities, smart homes, and niche applications like healthcare and industrial settings. We encourage companies to contact us if they would like to get some of the first Nucleo boards or more information.
Table of Contents
From STM32WL5 to STM32WL3: Finding a new balance of power
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).
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.
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.
