This is a small project based on the sparkfun nrf52480 mini which is based on Nordic Semiconductor's nRF52480 chip. This project can be used to implement any bike which provides a digital hall effect trigger for cadence and analogue signal for resistance / gear. Based on these inputs an ANT+ PWR and ANT+ SPD sensor can be developed using the awesome nRF52480 chip.
Also note, this project will require a programmer to program the Softdevice. To the best of my knowledge (and attempts) you cannot program the s340 softdevice without a programmer. I used the cheap educational segger mini if you are looking for a recommendation.
As ANT+ requires a license and registration as a developer, this project does not provide two crucial elements to make this successful;
- You need the Softdevice s340 to operate ANT on the nRF52480. This is ONLY available through thisisant.com.
- You need the ANT+ Network Num and set it in the project under #define ANTPLUS_NETWORK_NUM. Again this is ONLY available through registration and developer license agreement at thisisant.com. They are freely available behind the registration and license acceptance process. Note: You cannot distrubute these, and can only be used for educational, not-for-profit projects... exactly like this one.
To map the Speed in m/s to the Power rating I used a simple quadratic that mirrored some engineering work here. Improvements need to be made here I suspect. I will link the function to desmos in another update.
Calibration of the PWR curve is a hack at best until I get access to something better to qualify it. The calibration and auto-calibration feature of ANT+ PWR is not implemented, so this is another area of work. However I have set a table to reflect ADC values against PWR based on the bike I used, an older Keiser M3 spin bike (which my model is not for sale anymore but latest models are here - not even the latest models talk ANT+ natively.
The Keiser M3 has a circuit board that sends the signals, both cadence and resistance (which is a potentiometer), to the bike computer . For my use I simply tapped the 4 wire connection for input into the sparkfun nrf52480 mini. Specifically hall effect digital pin went to pin 23 (NRF_GPIO_PIN_MAP(0, 23)) and after supplying 3V3 and GND to the pot the wiper went to analog pin 7 (NRF_SAADC_INPUT_AIN7) which I think is pin 31. The sparkfun nrf52480 mini comes with a board header file which maps all the pins to common #defines used in the SDK. I've edited it a little but you can follow sparkfuns guide to set it up in your environment - note this project only caters for the armgcc build toolchain. Its free and most familiar to me and easy to access on OS X.
The project utilises the latest nRF5 SDK which at the time of authoring is 15.3.0
Finally this project has served my purpose very well, it registers both the Power and Cadence as an ANT+ PWR profile (Channel 0) and also provides Speed as an ANT+ SPD profile (Channel 1). This coupled with a ANT+ HRM (outside the scope of this project) and I was able to register it all on my Garmin Forerunner 935 watch. All whilst being able to Zwift at the same time using my computer with ANT+ USB dongle. Note: iOS and Android devices are not supported at this stage as I have not implemented the Bluetooth stack.
I upload the work in the hope that others will share and extend this work mainly in these areas I'd like to encourage;
- Enhancements to calibration (auto-calibration functionality) and quality of authentic PWR and SPD values.
- Leverage Bluetooth stack - its available in the Softdevice s340 but I have built strickly ANT+. This will help with native sync to iOS and Android apps and also allow for functional project sharing out of the box without ANT+ license restrictions.
- The Ultimate Goal - ANT+ FE-C. This is a computer controlled spec and will require the project to implement a stepper motor to increment and decrement resistance requests based on connected computer. I consider this to be the ultimate end game which the community can use to implement a FE-C stack and upgrade many old spin bikes to FE-C.
Cheers.