WIP - Puck.js reading CSC (cycling speed cadence) BLE sensor to replace bike computer head unit with Puck.js or (later) Pixl.js

Thanks for your answer!

Here is the complete code:

var actual_menu, gatt;
var last_wheel_event_time = 0, actual_wheel_event_time;
var last_cumulative_wheel_revolutions = 0, actual_cumulative_wheel_revolutions = 0, track_cumulative_revolutions = 0;
var delta_revolutions, delta_event_time, timer = -1;
var wheel_circumference = 2340;
var delta_time_in_ms, connected = false;

function connect() {
  print("Starting scan...");
  g.clear();
  var s = "Connecting...";
  g.drawString(s ,0 ,0); g.flip();
  try {
  NRF.requestDevice({ timeout:20000, filters: [{ namePrefix: 'Wahoo' }] }).then(function(device) {
  console.log(device);
  return device.gatt.connect();
  }).then(function(gatt_object) {
    gatt = gatt_object;
    s = "Looking for service...";
    g.clear(); g.drawString(s ,0 ,0); g.flip();
    return gatt.getPrimaryService("1816");
    }).then(function(service) {
      s = "Looking for char...";
      g.clear(); g.drawString(s ,0 ,0); g.flip();
      return service.getCharacteristic("0x2A5B");
    }).then(function(characteristic) {
      characteristic.on('characteristicvaluechanged', OnNotify);
      return characteristic.startNotifications();
      }).then(function() {
        connected = true;
        setDisplayMode("livedata");
        console.log("Done!");
        // Then call gatt.disconnect(); if/when you want to disconnect
        });
  } catch(error) {
      print("Sensor not found", error);
      g.clear(); g.drawString("No sensor found..." ,0 ,0); g.flip();
    }
}

function disconnect() {
  if (gatt) {
      gatt.disconnect();
  }
  connected = false;
  print("Connected: ", connected);
  setDisplayMode("menu");
}

function OnNotify(event) {
    //console.log("-> "+(event.target.value.getUint8(0, true)>>> 0).toString(2)); //characteristics flags
    actual_cumulative_wheel_revolutions = event.target.value.getUint32(1, true);
    actual_wheel_event_time = event.target.value.getUint16(5, true);
    //console.log("Cumulative wheel Revolutions: " + actual_cumulative_wheel_revolutions);
    //console.log("Last Wheel Event time: "+ actual_wheel_event_time + " ms");
    delta_revolutions = actual_cumulative_wheel_revolutions - last_cumulative_wheel_revolutions;
    //console.log("-> "+event.target.value.getUint16(7, true)); //crank
    //console.log("-> "+event.target.value.getUint16(9, true)); //crank
  	if (actual_wheel_event_time >= last_wheel_event_time) {
				delta_event_time = actual_wheel_event_time - last_wheel_event_time;
		} else {
				delta_event_time = 65536 - last_wheel_event_time + actual_wheel_event_time;
			}
    delta_time_in_ms =(delta_event_time / 1.024);
    //console.log("delta_time_in_ms:" + delta_time_in_ms);
    last_wheel_event_time = actual_wheel_event_time;
    last_cumulative_wheel_revolutions = actual_cumulative_wheel_revolutions;
    track_cumulative_revolutions += delta_revolutions;
}

var mainmenu = {
  "" : {
    "title" : "-- Main Menu --",
    "fontHeight" : 10
  },

  "Connect" : function () { setDisplayMode("connecting"); },
  "Disconnect" : function () { disconnect(); },
  "Live Data" : function() {setDisplayMode("livedata"); },
  "New Track" : function () {},
  "Toggle Backlight" : function() { LED1.toggle(); },
  "-> Settings" : function () {Pixl.menu(SettingsMenu); },
  //"Exit" : function() { Pixl.menu(); },
};

var SettingsMenu = {
  "" : {
    "title" : "-- Settings --",
    "fontHeight" : 10
  },
  "Set Wheel Circumference" : undefined, // do nothing
  "Set Total Distance Counter" : undefined, // do nothing
  "< Back" : function() { Pixl.menu(mainmenu); },
};

function showLiveData() {
  //print("showlivedata");
  g.clear();
  var s = "Cum. Wheel Revolutions: ";
  g.drawString(s ,0 ,0); //95 - g.stringWidth(s) g.getWidth()
  g.drawString(actual_cumulative_wheel_revolutions, 0, 11);
  var speed = delta_revolutions * wheel_circumference / delta_time_in_ms * 60 * 60 / 1000;
  s = "Speed: " + String(speed.toFixed(2));
  g.drawString(s, 0, 22);
  s = "Track distance: " + (track_cumulative_revolutions * wheel_circumference / 1000 / 1000).toFixed(2);
  g.drawString(s, 0, 33);
  g.flip();
}

function onInit () {
  require("Font8x12").add(Graphics);
  setDisplayMode("menu");
  setWatch(function () { setDisplayMode("menu"); }, BTN2, {repeat:true, debounce:50});
}

function setDisplayMode(displaymode) {
 print("setDisplayMode: ", displaymode);
 switch (displaymode) {
         case "switchToConnected":
           Pixl.menu();
           break;
         case "connecting":
           if (timer!==-1) {clearInterval(timer); timer = -1;}
           Pixl.menu();
           setTimeout(function() {connect();},1);
           break;
         case "livedata":
           print("livedata");
           Pixl.menu();
           if (timer==-1) {
             print("Set timer"); 
             timer = setInterval( function () {showLiveData(); }, 2000); 
             print("timer = ", timer);
           }
           break;
         case "menu":
           if (timer!==-1) {clearInterval(timer); timer = -1;}
           m=Pixl.menu(mainmenu);
           g.setFont8x12();
           m.draw();
           }
}

onInit();

Though sadly your idea with

setTimeout(connect, 1);

did not work out; returning the same error. Thanks again!