Messaging Accelerometer Data (Data piling up)

[SimonWdm]

Hey everyone,

for an application I need a more or less continuous stream of accelerometer data. I want the app to run all the time so I use a clockface. My approach is to use an accelerometer with 20 Hz and a batch size of 20 (so every second there's a readout).

Whenever the accelerometer has a readout, I message it to the Companion.

My problem is that the messaging seems to be very slow. So when the Companion received the first package, 5 more were sent. This leads to the unpleasant situation that I send 5 times more data than I receive. When the clockface crashes, all unreceived packages are lost.

I am really out of my wits and very grateful for any ideas.

Best

Simon

[JonFitbit]

Can you provide some code for your project? What format data are you sending?

It might be worth using an approach like this: https://www.npmjs.com/package/fitbit-asap

[SimonWdm]

Hey Jon,

sorry for the late reply. Got stuck in something... . I changed my sending strategy such that now I have a send/received ratio of 2/1 when I am constantly sending data from device to Companion. I am sending JSONs which I later forward to a web API.

I attach some code and thank you very much in advance for input.

Btw. the asap package is awesome, thanks for sharing it.

Cheers

Simon

#### APP ####

import asap from "fitbit-asap/app"
import { me } from "appbit";
import { Accelerometer } from "accelerometer";
import { Gyroscope } from "gyroscope";

// Disable app timeout
if (me.appTimeoutEnabled) {
  console.log("Timeout is enabled. Disabling it!");
  me.appTimeoutEnabled = false; // Disable timeout
} else {
  console.log("Timeout is disabled. Nice!")
}

// sensor settings
const samplerate = 20;
const batch = 20;
const settings = { frequency: samplerate, batch: batch };

// initialize sensors
let acc = new Accelerometer(settings);
let gyro = new Gyroscope(settings);

// norm function for sensors
function getNorm(x, y, z) {
  return Math.sqrt(Math.pow(x, 2) + Math.pow(y, 2) + Math.pow(z, 2))
}

// aux sender function
function send(data){
  // asap is more stable messaging
  // https://www.npmjs.com/package/fitbit-asap
	asap.send(data)	
}

// will later be sent to Companion
var send_array = {}
// serves as message ID
var counter = 0

acc.addEventListener("reading", () => {
	// initialize sending objects
	var data = {};
	data['endtime'] = new Date().getTime();
	for (let index = 0; index < acc.readings.timestamp.length; index++) {
    	data[acc.readings.timestamp[index]] = getNorm(acc.readings.x[index], acc.readings.y[index], acc.readings.z[index])
    };
    send_array['a'] = data
	}
)

gyro.addEventListener("reading", () => {
	// initialize sending objects
	var data = {};
	data['endtime'] = new Date().getTime();
	for (let index = 0; index < gyro.readings.timestamp.length; index++) {
    	data[gyro.readings.timestamp[index]] = getNorm(gyro.readings.x[index], gyro.readings.y[index], gyro.readings.z[index])
    };
    send_array['g'] = data
    send_array['ID'] = counter.toString()
    send(send_array)
    counter = counter + 1
    send_array = {}
	}
)

acc.start()
gyro.start()

#### COMPANION ####

import asap from "fitbit-asap/companion"
import * as messaging from "messaging";
import { me as companion } from "companion";

// to upload 
var uploadArray = []

// append incoming data to postData
asap.onmessage = function(evt) {
  const message = evt.data;
  // print chunk ID
  console.log('Companion: Receiving ' + message['ID']);
  uploadArray.push(message)
  if (uploadArray.length == 30 ){
  	console.log('Got ' + uploadArray.length.toString() + ' seconds')
    // upload to API
    const formData = new FormData();
    formData.append('name', 'New Approach ' + message['ID'])
    formData.append('json_string', uploadArray)
    fetch('https://my_api_adress', {method: 'POST', body: formData})
    uploadArray = []
  }
}