peleton.js

const SerialPort = require('serialport')
const Delimiter = require('@serialport/parser-delimiter')
const port = new SerialPort('/dev/ttyUSB0', {
  baudRate: 19200
})

var peletonData = {
  cadence: 0,
  power: 0
}

var peletonDelimiter = new Buffer('f6', 'hex');
const parser = port.pipe(new Delimiter({ delimiter: peletonDelimiter }))

parser.on('data', function (data) {
  switch (data[1]) {
    case 65:
      peletonData.cadence = decodePeloton(data, data[2], false)
      return
    case 68:
      peletonData.power = decodePeloton(data, data[2], true)
      return
  }
}) 

setInterval(function() {
  console.log(peletonData)
}, 250)

function decodePeloton(bufferArray, byteLength, isPower) {
  wholeValue = 1
  precision = 0.0
  accumulator = 0
  iteratorOffset = 3

  for (iteratorTemp = iteratorOffset; iteratorTemp < iteratorOffset + byteLength; iteratorTemp++) {
      offsetVal = bufferArray[iteratorTemp] - 48
      if (offsetVal < 0 || offsetVal > 9) {
          console.log("invalid value detected: ", offsetVal)
          exit()
      }

      if (!isPower || iteratorTemp != iteratorOffset) {
        accumulator += (offsetVal * wholeValue)
        wholeValue *= 10;
      } else {
          precision = wholeValue * offsetVal / 10.0
      }
  }

  return accumulator + precision
}