Controlling Other BLE Espruino Devices

There are two main ways for one Puck to control another:

• Using the built-in UART service
• Using custom services
• Using advertising and scanning

See the About Bluetooth page for a bit more information

We're just going to use the UART here because it's the easiest.

On the slave/peripheral Puck (to be controlled)

• Connect to the Puck with the Web IDE (if you have more than 2 Pucks, remember what it was called)
• Enter a function that you'll want to make available to the controlling Puck on the right-hand side of the IDE:

var on = 0;
function toggle() {
  on = !on;
  digitalWrite(LED, on);
}

• Click the Upload button
• Now disconnect.

On the master/central Puck (that will control the other)

• Connect to the master Puck with the Web IDE
• Enter the following code on the right-hand side of the IDE:

// Are we busy?
var busy = false;

// Function to call 'toggle' on the other Puck
function sendToggle() {
  if (!busy) {
    busy = true;
    digitalPulse(LED3, 1, 500); // light blue to show we're working
    NRF.requestDevice({ filters: [{ name: 'Puck.js 7fcf' }] }).then(function(device) {
      require("ble_simple_uart").write(device, "toggle()\n", function() {
        digitalPulse(LED2, 1, 500); // light green to show it worked
        busy = false;
      });
    }).catch(function() {
      digitalPulse(LED1, 1, 500); // light red if we had a problem
      busy = false;
    });
  }
}

// Call sendToggle when the button is pressed
setWatch(sendToggle, BTN, { edge:"rising", debounce:50, repeat: true });

• Replace the name of the Puck (Puck.js 7fcf) with the name of your Puck.
• Click the Upload button
• Disconnect if you want to (you don't have to)

Testing

• Now if you press the button on the Puck you're programming:
  • It'll flash Blue
  • The other Puck will turn Red
  • It'll flash Green
• Or, it might flash Blue and then Red - this shows the communications failed. After all, it is radio and isn't 100% reliable - you'll have to write code to retry until you're sure there is success.

Note: the function above is also having to check if there is a task in progress. If there is, NRF.requestDevice will immediately raise an exception saying that a BLE task is already in progress.

Making it faster

You probably noticed that it takes a while to control the other Puck. This is because it's having to use requestDevice to search for the Puck first, and then we need to connect to it.

To get a lot faster, we'll need to go a bit more low level than the ble_simple_uart module, and access the individual characteristics as shown on the About Bluetooth page.

• Reconnect to the 'master' Puck again (if you'd disconnected).
• Copy the following code onto the right-hand side

// Are we busy?
var busy = false;

// The device, if we're connected
var connected = false;

// The 'tx' characteristic, if connected
var txCharacteristic = false;

// Function to call 'toggle' on the other Puck
function sendToggle() {
  if (!busy) {
    busy = true;
    if (!connected) {
      NRF.requestDevice({ filters: [{ name: 'Puck.js 7fcf' }] }).then(function(device) {
        return device.gatt.connect();
      }).then(function(d) {
        connected = d;
        return d.getPrimaryService("6e400001-b5a3-f393-e0a9-e50e24dcca9e");
      }).then(function(s) {
        return s.getCharacteristic("6e400002-b5a3-f393-e0a9-e50e24dcca9e");
      }).then(function(c) {
        txCharacteristic = c;
        busy = false;
        // Now actually send the toggle command
        sendToggle();
      }).catch(function() {        
        connected=false;
        digitalPulse(LED1, 1, 500); // light red if we had a problem
        busy = false;
        if (connected) connected.disconnect();
      });
    } else {
      txCharacteristic.writeValue("toggle()\n").then(function() {
        digitalPulse(LED2, 1, 500); // light green to show it worked
        busy = false;
      }).catch(function() {
        digitalPulse(LED1, 1, 500); // light red if we had a problem
        busy = false;
      });
    }
  }
}

// Call sendToggle when the button is pressed
setWatch(sendToggle, BTN, { edge:"rising", debounce:50, repeat: true });

• Replace the name of the Puck (Puck.js 7fcf) with the name of your Puck.
• Click the Upload button
• Now press the button again - it'll be just as slow as before :(
• Now press it a few more times - now it's connected and has found the transmit characteristic, everything is really fast
• When you're done, type reset(). If you don't, even after you disconnect the IDE, the Puck will stay connected and will drain your battery