I carried on through the developer study guy and implemented the basic Light. The messaging flow is now making sense to me. I knew the Microbit’s 16KB of RAM wasn’t going to be enough for any real project, so I decided to bite the bulled and pick up a Adafruit nRF52832 device.
Ordered from www.coolcomponents.co.uk, they arrived pretty quickly. I plugged it in, downloaded the Bluefruit app from the app store and was able to discover and connect to the device pretty quickly. So far, so good.
Unfortunately, I couldn’t flash it my Zephyr project. More digging around, using the Nordic Tools and I discovered that the West tool couldn’t detect the device. Strange, as I could flash it with simple Arduino sketches. I trawled the documentation. Tried changing drivers. Updated the bootloader. Nothing had any effect.
During the umpteenth reading of the Zephyr docs, I finally realised why:
Flashing Zephyr onto the nrf52_adafruit_feather board requires an external J-Link programmer. The programmer is attached to the X1 SWD header.
I have emphasized external in the quote above. I totally missed that key piece of information. More googling and I learn that Segger J-Link is a special protocol and that a small unit is required to interface your computer with the board! Everything fell into the place. The different drivers and the talk of the SWD header.
Unfortunately, my Adafruit boards don’t have a SWD header. Fortunately, the board has space and solder pads for one to be added.
I found a J-LINK device on The PiHut which I ordered, along with a short cable. I’ll wait for that to arrive before I attempt to solder this header onto the board. I’m going to need some steady hands!!
J-Link Device arrived and connected up. Managed to solder on the header without any issue.
I think hooked up my newly purchased J-LINK device. Side node here – I ordered a serial cable with this as PiHut said it was recommended. One came in the box, so the extra one I ordered was redundant! I’ll be writing to them about that.
Running the nordic command shows it has found the J-LINK connector!
I was aware that the Expressif ESP32 supports the new Bluetooth LE Mesh protocol, and as Bluetooth Low Energy would help stretch battery life, it seemed like the natural place to start my investigations.
I was initially going to try the WiFi mesh, but it didn’t really seem to suit devices like temperature sensor as they are actually asleep most of the time. If nodes in the mesh keep turning on and off, the other devices in the mesh would be constantly reorganizing themselves to plug the gaps. I do want to learn about ESP’s WiFi mesh, but for now, I’ll focus on Bluetooth
Documenting my progress
Rather than try and put a post together at the end, I’m going to try and document my progress as I go, with additions to this post each time I do something significant.
I’ve already got the ESP-IDF environment setup and have two different dev boards. I’m going to try and approach this in stages
Copy one of the sample projects and get it running
Add another node
Send data from one node to another
Add MQTT and WiFi to get data out of the mesh
9th July 2019
I pulled down the ESP-IDF code from their mesh branch and spun up on the samples. After faffing around with the menuconfig settings, I got the Node example compiled and deployed onto the device. It also appeared appeared in the Nordic iOS Mesh App.
Once I tapped on the node, I was able to tap “Identify”, which pulled back more information. I think this is what novelbits called “Invitation”. I then tapped “Provision” and after a few seconds, and a lot of logging from the device, I had the first Node in my mesh!
Now that I had my first mesh node, I quickly realised why the Expressif code was only at version 0.6 – none of the provisioning data was being saved. This meant that each time I flashed the device, I had to provision it again. This became annoying after the fifth time, so I started digging into the actual provisioning process, to see if I could put in something temporary.
I was digging around on google and I came across the Zephyr RTOS. In their examples, they had a simple 2 node mesh demo. The readme page states that no provisioning is required, and whilst it’s insecure, it’s sufficient for the demo. In their code, I could see a few lines of code where they manually provision the device with their own network and device keys.
This seemed ideal for my tinkering. I also found reference to the Zephyr code in Expressif’s news release about their BLE Mesh, where they state they are basing their implementation on top of the Zephyr . This meant I could probably find simple code in the esp-idf repo.
Running this code on the device resulted in it saying that provisioning was complete.
After more digging around the ESP-IDF examples, I came across some testing code, which appeared to provision using the esp code.
Try as I might, I couldn’t get that to work. Just kept reporting an error of -22.
UPDATE 13th August: During some experimenting with how to bridge the mesh network with MQTT, I managed to get this code working eventually, meaning:
After more attempts to provision the device directly, I’ve decided to kinda give up. As I mentioned, the Zephyr code is easier for me to understand at this stage, so I’m going to try and get a build of the Zephyr samples running on my ESP32 boards.
After hours of playing around trying to get the Zephyr SDK compiling against the ESP32 toolchain, I decided to stop. I found an excellent resource at over on the Bluetooth SIG website, called “An Introduction to Bluetooth Mesh Networking“. The samples in their course use the Zephyr SDK and the BBC Microbit. I had a glance though it and most of the main concepts are covered, so I think I’ll order some BBC Microbits and run through it.
I also came across an interest post at https://hutscape.com/, which is worth checking out. The author, Sayanee, uses an Adafruit board to build a UV sensor. Pretty cool. At £26 (and no Friend Node support in the Nordic SDK), I decided against buying any for the time being.
I got a BBC Microbit and tried the Zephyr mesh_demo code. After more mucking around, I managed to flash it with their code.
As suggested by the Bluetooth study guide, I turned on the logging and then
Hardware development is tough! That said, these microbits are perfect for me to dabble in the fundamentals of Bluetooth Mesh and to get to grips with the models. Hopefully there is enough space for me to try my own code. Perhaps it’s possible to compress the Zephyr RTOS runtime down a little??
Been reading about how to figure out the size of the runtime. You just run the command ninja rom_report
I don’t know what those numbers actually mean. I had assumed bytes, but that would mean the bluetooth library, if measured in bytes, was around 50KB and I know that’s not right.
I experimented with the Zephyr mesh_demo sample, but couldn’t make it work. Kept getting error codes when trying to send messages. I tried to tweak it here and there, but I was just strumbling around in the dark. I returned, instead, to the Bluetooth developer guide and gave that go. The guide starts at the Switch module.
The sample code wasn’t up-to-date with the latest Zephyr code, so I had to tweak it somewhat, but I got it to compile and, amazingly, it worked.