Just a short blogpost following up on the Lora Backplane I designed.
One of the main concerns was temperature. And while I didn't think it would be much of an issue because it has to be in a sealed box it was overheating to around 80 degrees. However since changing the powersupply from 12v to 7.5 this has dropped dramatically to around 50 Degrees peak. Very acceptable :D
Otherwise the gateway has been working perfect and more reliably than my original Pi Zero setup over Wi-Fi.
Improvements still to do
Multi Packet Forwarder
I'm still trying to sort out to use the multi packet forwarder. Currently while I have been able to get it crashes with a segfault. I need to do some more debugging to solve this, originally when trying to compile some extra debugging stuff the gateway was crashing due to overheating so now the overheating problem is solved I should be able to debug it.
Even while I've created a SNAP, I'll likely have to still create an installer bash script which will help speed up the installation process by automatically installing the snap, and then ask questions to automatically generate the configuration files for you.
More power improvements
To be honest, the Nano Pi is overkill. With it's 4 Cores running at around 1Ghz and 512MB Of ram, it's overspecced by far. The memory usage also rarely goes over 200MB.
A quick sysbench of 10,000 primes on one thread took around 210 Seconds. Looking around online this is around the same (or a little bit faster) than a Pi Zero at 1Ghz too. However when we add multiple threads in it's only 57 Seconds.
So when I get the parts for the second one I'll experiment with turning 2-3 cores off to see if the power saving is worth it.
Another thing I haven't turned off is the wi-fi adaptor as I'm not using it at all.
Some Questions that I've been asked
A little FAQ
You've missed off the cost of the SD Card
Yes I have, this is partially deliberate as for this you don't need a big SD Card and I suspect most people that are into electronics of some kind will have an abundance of SD Cards. However if you add one one (Say £8) our total is still around £116 so within my original £110-120 bracket quoted.
Why did you not use [Insert SBC Name here]?
I looked at a lot of SBC Options before designing it, the main part I wanted was a single connector going into the box which had ethernet and power without having to use extra adaptors or connectors in the box.
I could for example have used a Raspberry Pi B+/2/3/3 B+ / Orange Pi Zero / Orange Pi Plus with a POE Adaptor which takes the cable in and outputs a micro usb and ethernet cable. However I wanted it to be all on one board.
I could have used one such as the Pi Zero however I'd have either have had to used SPI for ethernet (very slow) or wire up a USB Network controller (Pogo pin mechanical reliability in question).
I did originally plan to use an Onion Omega 2+ however had issues with the SPI Bus on it. The benefit of this would have been that it could use built in flash which the nano pi duo does not have however the SPI Bus not working correct was a major issue.
As mentioned above it also doesn't need to be faster, for example I could have looked at using the 3B+ as this came out just a few days before I placed the order for the PCBs, However the initial cost of the Pi (£30) plus the much higher power consumption & heat generation didn't seem ideal.
To make it clear, the main idea was to have one connector going into one board to provide power and ethernet, not to then have extra adaptors in a box.
What about Kersing's forwarder?
As mentioned above I'm half way there, just a few bugs in my compiling to sort out.
SD Cards are unreliable either because of the type of memory / socket they use
This is a bit of a complicated subject. I've had some Raspberry Pi's with SD Cards last ages without issues and others have issue. In this case not a lot of data is being written to the SD Card at all so I'd say its fine.
Mechanically I'm not concerned about the SD Card slot. Being in an enclosed box the SD Card isn't going to get knocked. Also due to the design of the Nano Pi Duo because the SD Card is on the bottom
I could look at putting some storage IC and a USB Controller on the PCB as the Nano Pi has 3 USB Sockets through the pin headers but this would increase the cost significantly.
Why not just use a switching regulator?
I did seriously consider it, however regulators I was finding either were very expensive (About £3-4) or required quite a few extra parts to make them work.
But, to repeat my original post. I want as little external noise as possible. Switching regulators while very effecicent are usually very noisy unless very well designed (I'm not an expert at all in them as I've designed 0), can require more expensive components and it's sometimes found that even in new audio and RF equipment linear regulators are still used because of this.