Choosing a LoRaWAN module

A project log for OpenAirMonitor

A solar-powered, outdoor air quality monitor that transmits data over LoRaWAN and Bluetooth LE

Gerrit NiezenGerrit Niezen 12/08/2021 at 10:200 Comments

If your electronics projects needs to talk to other devices, but you don't have access to WiFi, LoRaWAN is a great alternative. The Things Network (TTN) is a global collaborative Internet of Things ecosystem which allows devices to use the network for free. No payment or SIM cards are required like with NB-IoT or Helium, you just need to keep to the usage limits.

The problem is that there are very limited options for LoRaWAN modules, given the current global chip shortage. As I'm based in the UK, I'm looking specifically for 868MHz modules to use with the OpenAirMonitor.

The RN2483 LoRaWAN module from Microchip used to be the de facto option when you don't want to run a LoRaWAN stack on your microcontroller. Unfortunately they are out of stock until 2022 or later. Luckily there are other options, so let's have a look at what's out there.

RAK Wireless has a range of LoRaWAN modules where different microcontrollers are combined with LoRa chips. The RAK3172 is their first module that uses the STM32WL, combining a microcontroller and LoRa on the same chip. It comes preinstalled with a LoRaWAN stack, so you can use it with your own microcontroller over a UART interface.

Seeed Studio's LoRa-E5 module also uses the STM32WL chip, and is also controlled over a UART interface if you use the preinstalled stack. 

Unfortunately both the RAK and Seeed modules suffer from a high transmit power consumption bug, which look like it may not be able to fix in firmware without reducing the range significantly.

Ai-Thinker's Ra-07H uses the ASR6501 chipset which also combines a LoRa transceiver with a microcontroller, and can also be controlled over a UART interface.

Ebyte's E78 module is also based on the ASR6501 chipset. It appears that both the Ra-07H and E78 modules are compatible with TTN v3.

There are other LoRaWAN  modules out there, like Move Solutions' STM32WL-based MAWLE-C1, but the ones above are ones that were actually in stock at the time of writing.

In the end I went with Seeed Studio's LoRa-E5 module, as they have a range of different promotions going on at the moment and I intended to make use of their Fusion PCB Assembly Service. I bought my first batch of LoRa-E5 modules directly from their web shop, and they arrived relatively quickly.

For my first prototype PCB I used JLCPCB's assembly service, but had to solder the LoRa-E5 module and the MDBT42Q module myself, as they're not in JLCPCB's SMT parts library. For my second prototype revision I used Seeed's Fusion assembly service, as they currently have an offer for two free PCBA boards if it contains a LoRa-E5. I thought it was too good to be true, but I literally didn't have to pay anything to get the two prototype boards, including all the components.

During the design check they even found a footprint issue that wasn't discovered during the first prototype run, and where parts were out of stock they worked with me to find suitable alternatives. The only part that we couldn't find an alternative for was the MDBT42Q, for which there was no stock in the entire mainland of China. Luckily I had modules on hand, so had the board manufactured without the module and soldered it on myself.