My "Ultimate" Lora Gateway Backplane

My "Ultimate" Lora Gateway Backplane

A DIY Solution I'd be happy to use as a stable alternative to a premade.

I've been working on this project for about a month and a half now with changes along the way. If you follow me on twitter you'll have likely seen the progress I made. I've also been posting devleopment updates at https://hackaday.io/project/90405-ultimate-lora-gateway-backplane

This post will be a mix of a summary / analysis of the current design.

Designing the board

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I wanted to build a DIY Gateway solution which I'd be happy to put somewhere and leave. My current gateway is on the side of the garage but at the time I started developing this project I was planning to move it onto my roof. (Didn't happen due to another reason).

However as I was planning this I wanted a more reliable solution.

My design was to use a SBC of some kind, I wanted the SBC to have SPI and ideally some kind of built in networking. After lots of searching I found the Onion Omega 2, However due to some issues the SPI Bus just didn't work.

I then did some more searching and found the Nano Pi Duo, a H2+ Based SBC (Like the Orange Pi Zero) however in a Breadboard format, with the ethernet pins broken out like the onion omega. Ideal! I also know the SPI works fine on these chips as I've used my OPi 0 for my gateway before. I did look into an RPi based solution, however a zero would have had to have had SPI Ethernet (Max 10Mbits vs 100Mbits) or USB (Complicated). And the 3 B+ was launched around the same time I completed the other design, (And also costs more).

The next main consideration was power, I wanted to use POE of some kind. Originally I was planning on using a passive 5V POE method however this could have caused issues with voltage loss over long lengths of cable. So I decided on using between 9-12V with a onboard regulator.

This then lead onto comparing a linear vs a switching regulator. I chose the linear for a couple of reasons, being less noisy in theory than a switching, only being a couple of parts vs 5-10 components and I actually wanted some heat. One concern was during winter that it wasn't hot enough to keep itself warm enough with the previous solution I was using. Where as with heat being a side effect of linear regulators it could be used to it's benefit.

Finally I wanted this board to support both the main two DIY Gateway concentrators, these are the IMST IC880a and RAK831. This is for a simple reason of by having both supported by one board you can mix and match when you make more. For example I'll have one ic880a and one RAK831 gateway with both the rest of the hardware & software being identical.

Making the board

With all of my requirements set I designed the board in Eagle 7.7 and sent off to AllPCB to get fabbed up on Saturday. And they arrived on Wednesday!

I then started work on soldering them up, I did all of the SMT Components by hand and then just re-flowed them in my toaster oven to ensure a good solder. Followed by soldering all of the through header parts and it was complete!

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The nano pi fits on the back, with the radio of your choice on the front.

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picture of the nano pi duo on the back

ic880a
Picture of the ic880a on the front

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Picture of the rak831 on the front

Software

Aiming for my backplane to be "ultimate" with the idea being its easy to replicatefor other gateways. I wanted a simple method of installing the software on multiple.

For this I chose to create a "Snap" and use Ubuntu on the NanoPi DUO As the host OS. With lots of tweaking and compiling I had a Snap that I could install onto an SD Card image, change a couple of lines of config to identify each gateway seperately and then with a reboot the software would start automatically.

I originally tried to get the kersing multi packet forwarder working but kept getting issues with compliling. So for now I've just got it working using the classic semtech solution.

Analysis

So does it work?

Yep! It works perfect, the software has been stable as expected, the power over ethernet works perfect and an iperf test shows a speed of around 90Mbits, Almost the max for this connection and more than good enough for gateway usage.

It connects to a simple POE Injector which has a barrel jack, input and output socket. This connects to a Network Surge Protector and then finally to one of my network's switches.

My Raspberry Pi Solution kept crashing out on me recently too, so I replaced it with the new board outside, it just about squeezes into the box I have with the main bit being the network jack could possibly do with a slight adjustment. But much better than the previous setup I had.

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Board in gateway box outside

So a perfect success?

Maybe not perfect, currently it's depending on a lot more testing. One thing I mentioned is while I wanted the heat from the gateway from another angle its well, more heat in a box which is only 10x10CM. Not ideal. However this for example I plan to mitigate by swapping from my 12V Power supply to a 9V Power supply, at a theoretical maximum of 2A on the 5V Rail this decreases the dissipation from 14W to around 8W. A 7.5V PSU Should also be fine and drop it to 5W.

So far the only design issue has been that while the ic880a has headers on each side of the board so is mechanically stable just being plugged in. My drill hole to mount the other side of the RAK831 was misaligned. A simple fix and nothing major.

Final Notes

I'd say that I would be happy building more DIY Gateways with this as the backplane PCB, There's some advantages being that everything is connected to the one board, the NanoPi Duo is mounted to the back using a mechanically strong method, the mix of LEDs throughout the board also helps with debugging.

If you are interested in possibly buying one of these PCBs do get in contact. I might do a small batch of them soon.

Pricing

And finally, the pricing. One of the major advantages of a DIY Gateway over a pre-built is the price. So here's the costing.

For this I have included the price of the Radio, NanoPi Duo and Backplane PCB. The antenna is not included as with a prebuilt this is usually seperate. I also haven't included the box or POE Hardware as sometimes these are also extras with prebuilts depending on your setup.

A quick calculation later
Screenshot-from-2018-03-30-14-06-34

It works out at around £110-120 depending on a few components, if you use the ic880a its more around £175,

For comparison a The Things Network Gateway costs around £300. So this is much cheaper! You can build between 2-3 gateways for the same price which will work in theory just as well. However if you just want something that you can order online today, and have arrive tomorrow? The Things Gateway is for you.

That's it for now!

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