The Seeed Studio LoRa-E5 Hardware
The STM32WLE5 CPU+LoRa radio chip is the basis for Seeed Studio’s LoRa-E5 module. They’re both very interesting so I’m going to walk through what the Lora-E5 is and how to develop apps for it and for the STM32WL series.
This post is specifically about the hardware. The following few posts are about the software.
What is the CPU?
The STM32WLE5 chip line integrates a Semtech SX126x LoRa chip (or at least the IP and some silicon) and an Arm Cortex M4 with 256K flash and 64K RAM at 48MHz. It’s quite a package, with multiple internal power supplies for the LoRa current, and reportedly a battery charger. Even built-in TCXO (temperature compensated crystal oscillator) control to keep the radio on-frequency.
The default firmware is a turnkey LoRaWAN node with a simple serial AT interface.
What is a Lora-E5?
The LoRa-E5 packages an STM32WLE5 with the appropriate RF matching components, switches, and crystals/oscillators to be a self-contained LoRaWAN node subsystem. Seeed Studio’sGrove (I2C) LoRa adapter is just a Lora-E5, a few simple components and a bad antenna. The HF model runs 868–930MHz (covering both EU and US ISM bands).
Usefully, the serial debug pins and a ROM bootloader are available on the chip (and the Lora-E5 module) so you can overwrite the existing LoRaWAN node application with whatever you want — and 256KB is a lot of flash.
STM/Seeed provide a few simple startup applications including the node app, a sparse Wiki, and then you’re on your own. There is no schematic or layout or even block diagram of the Lora-E5 module so good luck there. Nevertheless, and kudos to the team, the applications actually compile and run so they provide an excellent learning resource.
Even better, Seeed has done the work to create a basic working board definition for use with the Zephyr OS so you don’t have to rely on STM32Cube — which I’ll discuss later.
At the moment I’m basing this on a small amount of testing (and NO RF testing) along with reading the basic specs. Over time I may change some of this but…
The STM32WLE5 looks like an awesome chip. If it had a built-in USB interface it would be almost perfect for creating mobile LoRaWAN sensor nodes. In my opinion it’s the most useful LoRa chip available today.
Next, customizing VSCode to build and debug a Zephyr application.