Low-Cost LoRaWAN Gateways!

I saw in an e-mail an advert for LoRaWAN gateway modules, so I took a quick peek, and was surprised at how low-cost they had become. These can be used with any computer, such as a Raspberry Pi, to wirelessly monitor or control sensors and actuators, both DIY and ready-made.

In the not-too-distant past, the average price was about £200 GBP to build up a LoRaWAN gateway with no outdoor-friendly enclosure. Now it’s less than half that price using these LoRaWAN modules which come in 868 MHz and 915 MHz variants.

For anyone unfamiliar with it, LoRaWAN is a wireless network that allows for small quantities of information to be sent to or received by LoRaWAN nodes.

A typical LoRaWAN node (blue dashed line below) could consist of a sensor, microcontroller and wireless transceiver, all operating from a battery that could last years. The node will communicate with a LoRaWAN network. There are several providers, and you’d need to check coverage maps to see if any provider has gateway devices installed nearby. Those gateway devices connect to the Internet, and the data makes its way to servers owned by the provider. Some providers offer free accounts, others are paid. You can log in and view your LoRaWAN node data, or connect to it using an application programming interface (API).

If there isn’t a gateway near you, then you can install your own (green dashed line above), and configure it to connect to the service provider infrastructure via the Internet. I currently use a LoRaWAN gateway built around a Raspberry Pi with a RAK2245 HAT board plugged on top. With that, I can use homemade LoRaWAN nodes (for instance Pico IoT LoRaWAN EasyNode  ) or commercial off-the-shelf ones.

The RAK2245 and Raspberry Pi gateway has been very reliable. I have no issues with it, except that it’s more expensive than I’d like, so I didn’t want to purchase another RAK board until prices come down.

The RAK2245 HAT board uses an older chip from Semtech, called SX1301. The Elecrow modules use the newer SX1302. The Elecrow module was low-cost, at about $24. This is what the module looks like with the metal can lifted:

It looks very well built, and I believe it is closely following reference designs from Semtech. At the top-left is the SX1302 “baseband processor” chip that performs the modulation/demodulation for multiple channels (LoRaWAN gateways can manage communication from many nodes simultaneously; it’s not just tuned to one channel). To the right of that, are two SX1250 chips that take the baseband modulated information and up-convert it to the radio frequencies that are required (it is around 868 MHz in some locations such as Europe, and 915 MHz in other such as USA). Further to the right is a Skyworks SKY66420 chip that contains transmit/receive amplifiers and switching, and it is wired to an antenna connector at the far right. The SKY66420 accepts RF from the topmost SX1250 chip, and amplifies it and directs it to the antenna. For RF reception, the chip is attached to both SX1250 chips (you can see the RF signal split in the center of the board).

At the lower-left of the board, the missing chip is used for a USB interface that I didn’t purchase; I wanted to use the SPI interface that the SX1302 chip supports directly. The other missing chip to the right of that is SX1261, which is used for providing more optimal radio usage, by listening to the channels to provide a quality/interference type of assessment.

There are no components on the underside of the board:

To use the board, it would need to be wired via SPI to a computer, running LoRaWAN gateway software. There is a Pi HAT adapter board that could be used. I didn’t purchase it (I was hoping to just DIY it), but due to lack of time I’ve decided to just order it for now; it’s about $17.

(image source: Elecrow website)

I think that if anyone is interested in LoRaWAN, I don’t think it’s going to get much cheaper to build a gateway! Obviously for a real deployment ready-made gateways would be used (and many are ruggedized for outdoor use; Seeed Studio has some nice outdoor-capable gateways for $399 which is low-cost compared to some of the competition). However some of the indoor gateways are very low cost, ballpark £100. I wanted to go the Pi route however, just to learn a bit about the underlying code, and perhaps peek at the SPI traffic too.

In total, the LoRaWAN gateway module, plus the Pi HAT, costs about $42 including shipping. Add on the cost of a Pi and a basic antenna, and the total is easily under £100 GBP! Since it doesn’t require the latest Pi for operation (I’m using the Pi 3 with the RAK module), then if you already have a Pi then it could be repurposed for this.

Currently I don’t know how easy/hard it is to set up, and how it will perform. I’m hoping it’s as good as the RAK module, I’ve never used any Elecrow modules before, but I did purchase a childrens project kit from them in the past, and it was pretty decent. Of course that means absolutely nothing where RF is concerned! Anyway, fingers crossed, and I'll report back after I've given it a go.

Thanks for reading!