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NarfButt! An nRF51822 BTHome Button

This is (currently a proof-of-concept) implementation of the BTHome protocol for nRF51xx chips (in particular the nRF51822).

The idea is to create a BLE (Bluetooth Low Energy) remote control with buttons (and perhaps other sensors) that sends data to HomeAssistant via ESPHome Bluetooth Proxies.

Using the BTHome protocol means that no integrations are required, and the device will show up automatically in Home Asssistant ready for creating automations.

  +----------+          +-----------+           +-----------+
  | NarfButt |          |  ESPHome  |           |   Home    |    **~*~*~**
  | Remote   | -(ble)-> | ble_proxy | -(wifi)-> | Assistant | -> * MaGiC *
  +----------+          +-----------+           +-----------+    **~*~*~**

My personal goal is to create super-affordable remote control buttons for placing over the top of existing light switches etc for home-automation projects.

Status

  • Proof of concept. Sends valid BTHome v2 unencrypted advertisements, with battery percentage level and a bogus temperature measurement that increments with each packet sent.

uFAQ

  • What's with the name?
    • Narf! is the nonsense-word exclamation / catchphrase of Pinky from Pinky and the Brain.
    • Butts are funny and very unprofessional.
    • nRF51822... nrf... Narf.
    • Button... Bluetooth... bt... butt
  • Why not zigbee, zwave or wifi remotes?
    • Cost. I want 6 or so buttons for under AU$10. Tradfi buttons are sexy, but too expensive to replace lots of wall switches (for me, anyway).
    • Redundancy - zigbee networks have only one controller node, despite having redundant paths to that node. Using BLE Proxies means I have many (currently half a dozen or so) BLE receivers that forward their data via one of multiple wifi APs, at which point my ethernet network is pretty reliable. I don't know how zwave works, but see point 1 above.
    • Wifi's no good because of power consumption, as I want these remotes to be easily thrown anywhere around the house. A CR2032 in this device should last a year or so if I haven't left too many bugs in the code.
  • What modules should I buy?
    • The cheapest I've found are the HOLYIOT-17051-NRF51822 which are a little breakout board with annoyingly small 2.0mm-pitched pins. They seem to work just fine. There are also some smaller modules with castellated edges which might be easier to mount - I plan to make a board layout for those too - oddly the smaller modules are a bit more expensive, but still quite cheap.

Building the Firmware image

This is a platformIO project with VSCode plugins, so opening with with VSCode is probaby going to give the smoothest experience to try it out.

Please forgive my atrocious C++ code, I'm a greybeard SysAdmin not a programmer :-) PR's VERY welcome!

Flashing

I use a clone STLink V2 flasher and OpenOCD.

This connects with just the GND, 3.3v, SWDIO and SWCLK lines.

Update! The built-in stlink flashing in vscode works. Just doing a build and upload cycle in vscode should get the firmware on to your device. However, if you want to do it without vscode or do something more specific, then...

The modules need to be mass-erased before flashing. Sometimes this part is hard to get working, but ultimately what I've found works is:

openocd -f interface/stlink-v2.cfg -f target/nrf51.cfg \
    -c "tcl_port disabled" \
    -c "init; reset halt; nrf51 mass_erase; reset halt;" \
    -c "program ./.pio/build/waveshare_ble400/firmware.hex; reset; exit"

(You can just run ./tools/flashit.sh to run exactly the above, or some later variant that I've forgotten to update here).

Currently I'm having issues running openocd interactively, it seems to disconnect after a few seconds, but using the command above so it all happens immediately is working fine for me.

Building the Hardware

  • There's a PCB layout in the folder, which is my current design for a general-purpose 6-button switch for placing over existing light switches, or using as a stand-alone remote control. I expect to create some variations of this, in particular a version with a rotary encoder might be fun to play with.

PCB Prototype Back PCB Prototype Front

  • Note that the buttons are surface-mounted on the "back" while the NRF module is mounted on the non-trace side. This can be a bit confusing when doing the pcb layout!

TODO's (please!)

  • learn c.
  • learn cpp.
  • add buttons, sleep mode etc.
  • turn this into a usable basis for my own and others' projects.
  • document how to build and flash a device (I think I used openOCD but frankly it was months ago and I am just whacking this up on GH now).
  • Implement BTHomeV2 Encryption
  • Fix module width in PCB design
  • Try to take over the world. Narf!
  • Choose a license. I haven't chosen a license yet. I need to check the sources I pilfered from (there are comments in the code) and choose a permissive license that fits the requirements of the stolen code prior art.