Read speed from ELM327 over TCP/IP

readspeed.ts

const { createConnection } = require("net")
const { format } = require("util")

const socket = createConnection({ port: 35000 })

const CURRENT_DATA_MODE = "01"
const CURRENT_DATA_MODE_RESPONSE = "41"
const VEHICLE_SPEED_PID = "0D"

const debounceWait = (time: number) => {
  let readTimeoutHandle = -1

  return (fn: Function) => {
    clearTimeout(readTimeoutHandle)
    readTimeoutHandle = setTimeout(fn, time)
  }
}

const writeDelay = debounceWait(100)

const requestSpeed = () => {
  const message = `${CURRENT_DATA_MODE} ${VEHICLE_SPEED_PID}\r`
  console.log(format("<< %s", message))
  socket.write(message)
}

socket.on("data", (data: Buffer) => {
  if (data.includes('>')) {
    writeDelay(requestSpeed)
  }

  const messages: Array<string> = data
    .toString("utf8")
    .split(/[\r\n]+/g)
    .filter(v => v.length)

  const responses = messages
    .map(message => message.split(" "))
    .filter(segments => segments[0] === CURRENT_DATA_MODE_RESPONSE)

  const speedResponses = responses
    .filter(res => res[1] === VEHICLE_SPEED_PID)

  speedResponses
    .forEach(segments => {
      const speedHex = segments.slice(-1).join(" ")
      const speed = parseInt(speedHex, 16)
      console.log(format(">> Speed: %s", speed))
    })
})

socket.write(`AT Z\r`)