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0.1.8 • Public • Published

Zwack BLE

Simulate/Implement a Bluetooth Low Energy sensor that can send:

  • Cycling Power and Cadence (CSP Bluetooth profile)
  • Running Speed and Cadence (RSC Bluetooth profile)

Zwack has many possible uses, here are some examples:

  • Simulate an indoor bike trainer (turbo) generating cyclist power and cadence data to test bike computers fitness, or virtual indoor bike apps.
  • Simulate a runner's speed and pace test bike computers fitness, or virtual indoor bike apps.
  • Integrate a common treadmill with Zwift, sending data from the treadmill to the Zwift game via bluetooth


At this time Zwack runs succesfuly on Mac OSX and Raspberry PI. Should run on Windows but it hasn't been tested. If it works let me know.


Install from npm

npm i zwack

or clone this repo and run

npm install

You may need to install Xcode on Mac to compile the bleno Bluetooth module.

Debug Flags

You can see a lot of debug information if you run the simulator or your app with the DEBUG environment variable set to

  • csp - Cycling Power and Cadence messages
  • rsc - Running Speed and Cadence messages
  • ble - Bluetooth low energy messages


DEBUG=rsc npm run simulator

You'll see something similar to this

rsc [Zwack notifyRSC] {"speed":4.4703888888888885,"cadence":180} +0ms
rsc Running Speed: 4.4703888888888885 +2ms
rsc Running Cadence: 180 +0ms
rsc [Zwack notifyRSC] {"speed":4.4703888888888885,"cadence":180} +1s
rsc Running Speed: 4.4703888888888885 +0ms

Using the simulator

Start the simulator by executing:

npm run simulator

On a different machine start your fitness app, bike computer or indoor virtual bike simulation software, like Zwift, and pair up the Zwack BLE sensor. The sensor name should be Zwack, it may have some numbers added to the name or you may see the host name of the computer running zwack. It all depends on the operating system you're uing to run Zwack.

If your indoor biking software does not detect the BLE sensor, disable, then enable, the Bluetooth on the machine where Zwack is running and retry to discover and connect to the sensor again.

The ZwackBLE sensor may show up as Zwack or has the host name of the machine running Zwack. This is normal.

Updating simulation parameters

List of Available Keys
  c/C - Decrease/Increase cadence
  p/P - Decrease/Increase power
  s/S - Decrease/Increase running speed
  d/D - Decrease/Increase running cadence  

  r/R - Decrease/Increase parameter variability
  i/I - Decrease/Increase parameter increment
  x/q - Exit

Pressing c on your keyboard will decrease the cadence, conversly pressing C (upper case) will increase simulated cadence. Same thing for power by pressing p or P.

The variability parameter will introduce some random variability to the cadence and power values, so they don't remain constant all the time. If you lower the variability to 0 the cadence and power values will remain constant.

Press x or q to exit Zwack.


Requires NodeJS, and should run in all Bleno (the base BLE module) supported platforms, which are Mac, Windows or Raspberry Pi.

Zwack cannot run on the same computer as the fitness or virtual indoor bike app, you'll need to run them on different systems.


Initial prototype based on ble-cycling-power code from olympum.


npm i zwack

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