bangle.js 2 - simple BLE example

[janrakete]

Hello everyone,

I am looking for a very simple BLE example.

I want to program an app that sends random integer values via BLE. I have the LightBlue app on my smartphone to receive them.

So I want to start LightBlue on my smartphone and then connect to the bangle app. Now I want to subscribe to a characteristic in LightBlue and see the respective random value from the bangle App.

I've tried many things, but I always fail because the console.log output is included in the packet to be sent. I have no idea why.

[gfwilliams]

Do you have the code you're using? If you are using the default Nordic uart characteristic then that's what the console is on by default so yes, console.log will appear on there.

You could just not log though, and use Bluetooth.println to write directly, or swap the console to somewhere else with something like Terminal.setConsole() (the screen)

But if you want a new characteristic that you have complete control of writing to, check out the example at https://www.espruino.com/Reference#l_NRF_updateServices - that should work fine

[janrakete]

Hi,

this is my code:

(() => {
  // ===== Display helper =====
  let log = [];
  function drawLog(msg) {
    log.push(msg);
    if (log.length > 5) log.shift();
    g.clear();
    g.setFont("6x8",2);
    g.drawString("BLE demo",10,10);
    g.setFont("6x8",1);
    let y = 30;
    for (let m of log) { g.drawString(m,10,y); y+=12; }
    g.flip();
  }

  drawLog("Starting...");

  // ===== BLE Setup =====
  const SERVICE_UUID = "6e400001-b5a3-f393-e0a9-e50e24dcca9e";
  const TX_UUID      = "6e400003-b5a3-f393-e0a9-e50e24dcca9e";

  NRF.updateServices({
    "6e400001-b5a3-f393-e0a9-e50e24dcca9e": {
      "6e400003-b5a3-f393-e0a9-e50e24dcca9e": {
        readable:true,
        notify:true,
        value:""
      }
    }
  }, { advertise:["6e400001-b5a3-f393-e0a9-e50e24dcca9e"] });

  // ===== Send interval ID =====
  let intervalId;

  // ===== On BLE connection =====
  NRF.on("connect", () => {
    drawLog("Connected!");

    // wait 0.5s to let client subscribe to notifications
    setTimeout(()=>{
      if (intervalId) return;
      intervalId = setInterval(()=>{
        const value = Math.floor(Math.random()*10)+1;
        const jsonStr = JSON.stringify({t:"random",v:value}) + "\n";

        try {
          // Always update TX value on BLE service
          NRF.updateServices({
            "6e400001-b5a3-f393-e0a9-e50e24dcca9e": {
              "6e400003-b5a3-f393-e0a9-e50e24dcca9e": { value: jsonStr }
            }
          });
          drawLog("TX: "+jsonStr.trim());
        } catch(e) {
          drawLog("TX error: "+e);
        }
      },3000);
    }, 500);
  });

  NRF.on("disconnect", ()=>{
    drawLog("Disconnected");
    if (intervalId) {
      clearInterval(intervalId);
      intervalId = null;
    }
  });

})();

[gfwilliams]

Ahh, ok, so what you've done is attempt to recreate the Nordic UART service yourself, which Espruino already provides out of the box. So then it's not creating anything new but is sharing the service with the built-in one which console.log/etc go to by default.

I'd suggest you either:

• Use your own Characteristic UUIDs (you can just use a random sequence of digits) and then you won't get any overlap
• Remove all the NRF.setServices/updateServices code, and just do Bluetooth.print(jsonStr) instead. If you're printing anything to the console, add Terminal.setConsole() in the connect handler to ensure that whatever gets printed just goes to the LCD, but just bear in mind that when your app is running and you connect you'll be unable to upload new code to it as you'll have removed the communication method.

... it's also possible to disable the built-in UART and then use your existing code but I wouldn't advise that, as Espruino handles the built-in UART much more efficiently, so you might as well use it if you want those characteristics.

[janrakete]

Many thanks, it's working now (example at the bottom).

My last question: You mentioned own Characteristic UUID anstead of just 6e40001... . This would be very convenient for me, as I would like to transfer several different values in the final app. Then each value could have its own characteristic. How can I achieve this based on the code below?

(() => {
  function log(msg) {
    g.clear();
    g.setFont("6x8", 2);
    g.drawString("BLE println()", 10, 10);
    g.setFont("6x8", 1);
    g.drawString(msg, 10, 40);
    g.flip();
    Bluetooth.println(msg);
  }

  log("Waiting for BLE...");
  NRF.on("connect", () => {
    log("Connected!");
    setInterval(() => {
      const val = Math.floor(Math.random() * 10) + 1;
      const json = JSON.stringify({ type: "value", v: val });
      Bluetooth.println(json);
      log("TX: " + val);
    }, 3000);
  });

  NRF.on("disconnect", () => log("Disconnected"));
})();

[gfwilliams]

Then each value could have its own characteristic

You might be better off just outputtiing on the same characteristic, but tagging your output line:

• JSON.stringify({ type: "val1", v: val });
• JSON.stringify({ type: "val2", v: val });

then it's easy enough to pull apart at the other end, and very extensible.

How can I achieve this based on the code below?

You actually want to use the code you had previously where UUIDs are explicitly defined, and just replace the UUIDs in it with your own (you can find 'random uuid generators' online) and replace chars 5..8 with 0001/0002/etc like is done already.