While waiting for my flic.io buttons to turn up I’ve been playing with building my own Bluetooth Low Energy devices.
Since I already had a couple of sensors hooked up to publish their values via MQTT I thought I would try and build a bridge between MQTT and BLE.
I’m using a Raspberry Pi, a Bluetooth 4.0 USB dongle and a NodeJS npm module called bleno.
It turned out to be petty easy, first a short file to set up the BLE service and connect to MQTT:
var util = require('util');
var bleno = require('bleno');
var mqtt = require('mqtt');
var BlenoPrimarySerivce = bleno.PrimaryService;
var TopicCharacteristic = require('./topicCharacteristic');
var config = require("./config");
var client = mqtt.connect(config.broker);
var topicCharacteristic = new TopicCharacteristic(config);
client.on('connect', function(){
client.subscribe(config.topic);
});
client.on('message',function(topic, message){
topicCharacteristic.update(message);
});
bleno.on('stateChange', function(state){
if (state === 'poweredOn') {
bleno.startAdvertising('mqtt', ['ba42561bb1d2440a8d040cefb43faece']);
} else {
bleno.stopAdvertising();
}
});
bleno.on('advertisingStart', function(error){
if(!error) {
bleno.setServices([
new BlenoPrimarySerivce({
uuid: 'ba42561bb1d2440a8d040cefb43faece',
characteristics: [
topicCharacteristic
]
})
]);
}
});
And then something to add the characteristic for the topic:
var util = require('util');
var bleno = require('bleno');
function TopicCharacteristic(config, client) {
bleno.Characteristic.call(this, {
uuid: '6bcb06e2747542a9a62a54a1f3ce11e6',
properties: ['read', 'write', 'notify'],
descriptors: [
new bleno.Descriptor({
uuid: '2901',
value: 'Topic: ' + config.topic
})
]
});
this._value = new Buffer(0);
this._updateValueCallback = null;
this._client = client;
this._topic = config.topic;
}
util.inherits(TopicCharacteristic, bleno.Characteristic);
TopicCharacteristic.prototype.onWriteRequest = function(data, offset, withoutResponse, callback) {
this._value = data;
client.publish(this._topic, data);
callback(this.RESULT_SUCCESS);
}
TopicCharacteristic.prototype.onReadRequest = function(offset, callback) {
callback(this.RESULT_SUCCESS, this._value);
}
TopicCharacteristic.prototype.onSubscribe = function(maxValueSize, updateValueCallback) {
this._updateValueCallback = updateValueCallback;
}
TopicCharacteristic.prototype.onUnsubscribe = function () {
this._updateValueCallback = null;
}
TopicCharacteristic.prototype.update = function(value) {
this._value = value;
if (this._updateValueCallback) {
this._updateValueCallback(this._value);
}
}
module.exports = TopicCharacteristic;
I’ve used 2 randomly generated UUIDs, one for the service and one for the characteristic.
The code should allow you to read the last value published, publish a new value and subscribe to notifications when new values arrive.
I pulled together a quick Android app to subscribe to the notifications and update when a new value is published and it seams to be working well.
The code is all up on Github and on npmjs so feel free to have a play.
You can test it with the Bluez gatttoool.
[hardillb@bagend ~]$ gatttool -b 00:1A:7D:DA:71:15 -I
[00:1A:7D:DA:71:15][LE]> connect
Attempting to connect to 00:1A:7D:DA:71:15
Connection successful
[00:1A:7D:DA:71:15][LE]> primary
attr handle: 0x0001, end grp handle: 0x0005 uuid: 00001800-0000-1000-8000-00805f9b34fb
attr handle: 0x0006, end grp handle: 0x0009 uuid: 00001801-0000-1000-8000-00805f9b34fb
attr handle: 0x000a, end grp handle: 0x000e uuid: ba42561b-b1d2-440a-8d04-0cefb43faece
[00:1A:7D:DA:71:15][LE]> characteristics
handle: 0x0002, char properties: 0x02, char value handle: 0x0003, uuid: 00002a00-0000-1000-8000-00805f9b34fb
handle: 0x0004, char properties: 0x02, char value handle: 0x0005, uuid: 00002a01-0000-1000-8000-00805f9b34fb
handle: 0x0007, char properties: 0x20, char value handle: 0x0008, uuid: 00002a05-0000-1000-8000-00805f9b34fb
handle: 0x000b, char properties: 0x1a, char value handle: 0x000c, uuid: 6bcb06e2-7475-42a9-a62a-54a1f3ce11e6
[00:1A:7D:DA:71:15][LE]> char-write-req 0x000d 0300
Characteristic value was written successfully
Notification handle = 0x000c value: 42 61 72
Notification handle = 0x000c value: 48 65 6c 6c 6f 57 6f 72 6c 64
Notification handle = 0x000c value: 54 65 73 74 69 6e 67 20 31 32 33
[00:1A:7D:DA:71:15][LE]>
[00:1A:7D:DA:71:15][LE]> quit
The lines that start Notification handle contain the bytes published, in this case
- Bar
- HelloWorld
- Testing 123
MQTT
Node-RED
Owntracks