Is it possible to use the RasPi 3 as a Bluetooth LE sensor?

Question

I'd like to add a LDR, Humidity and Temperature sensor, as well as some buttons to the Raspberry Pi 3. I mean, wire them to it (I've done that many times before).

Then the RasPi should be able to advertise itself via its integrated BT to a phone when the phone (an app, as it differs from normal Bluetooth) is scanning for Bluetooth LE devices, and ultimately connect to the phone (btgBluetoothGatt = device.connectGatt(context, false, btGattCallback); on Android), so that the phone can receive those sensor data as if it were a heart rate monitor or a speed and cadence sensor.

Is this possible? Where do I start with it?

I'd also prefer to use Python when possible.

Answer 1

I am busy finishing a project that does something similar. My project runs terminal command received by a client, allowing them to access the Pi without the need for 'cluttery' keyboards, mice and screens. The Pi will run the command and send the result back to the client device.

I have the Android, iOS and NodeJS code publicly on my GitHub account. I am not sure how you would do this in Python (perhaps this library) but I am fairly certain it'll end up looking similar. My work is heavily dependant on the NodeJS bleno library.

This code allows the Raspberry Pi 3 to advertise itself as a (BLE) peripheral, which your phone can connect to and read the data. The Android and iOS code is a little bad in the sense that:

1. They hold on to the connection, preventing other devices to connect. A BLE client should connect, get it's info, and then disconnect
2. The communication serialisation is wasteful, I use a whole message of a single character to represent the beginning and end. It should indicate how many blocks are being sent at the beginning and send that.
3. The iOS project is VERY basic, I haven't touched it since deciding what to do with the peripheral.

Anyway, here is the NodeJS code if it helps at all.

var bleno = require('bleno');
var exec = require('child_process').exec;

var CHUNK_SIZE = 20;

var Descriptor = bleno.Descriptor;

var deviceName = 'RaspberrPi3';
var myId = '4afb720a-5214-4337-841b-d5f954214877';
var data = new Buffer('Send me some data to display');
var output = "";
var updateCallback;

var terminalCallback;
var terminalResponse;

var START_CHAR = String.fromCharCode(002); //START OF TEXT CHAR
var END_CHAR = String.fromCharCode(003);   //END OF TEXT CHAR

function sliceUpResponse(callback, responseText) {
    if (!responseText || !responseText.trim()) return;
    callback(new Buffer(START_CHAR));
    while(responseText !== '') {
        callback(new Buffer(responseText.substring(0, CHUNK_SIZE)));
        responseText = responseText.substring(CHUNK_SIZE);
    }
    callback(new Buffer(END_CHAR));
}

var terminal = new bleno.Characteristic({
    uuid : '8bacc104-15eb-4b37-bea6-0df3ac364199',
    properties : ['write','read','notify'],
    onReadRequest : function(offset, callback) {
        console.log("Read request");
        callback(bleno.Characteristic.RESULT_SUCCESS, new Buffer(terminalResponse).slice(offset));
    },
    onWriteRequest : function(newData, offset, withoutResponse, callback) {
        if(offset) {
            callback(bleno.Characteristic.RESULT_ATTR_NOT_LONG);
        } else {
            var data = newData.toString('utf8');
            console.log("Command received: [" + data + "]");
            dir = exec(data, function(err, stdout, stderr) {
                if (err) {
                    var stringError = JSON.stringify(err);
                    console.log(stringError);
                    callback(bleno.Characteristic.RESULT_SUCCESS);
                    terminalResponse = stringError;
                } else {
                    console.log(stdout);
                    callback(bleno.Characteristic.RESULT_SUCCESS);
                    terminalResponse = stdout;
                }
                if (terminalCallback) sliceUpResponse(terminalCallback, terminalResponse);
            });
        }
    },
    onSubscribe: function(maxValueSize, updateValueCallback) {
        console.log("onSubscribe called");
        terminalCallback = updateValueCallback;
    },
    onUnsubscribe: function() {
        terminalCallback = null;
        console.log("onUnsubscribe");
    }
});

bleno.on('stateChange', function(state) {
    console.log('on -> stateChange: ' + state);
    if (state === 'poweredOn') {
        bleno.startAdvertising(deviceName,[myId]);
    } else {
        bleno.stopAdvertising();
    }
});

bleno.on('advertisingStart', function(error) {
    console.log('on -> advertisingStart: ' + (error ? 'error ' + error : 'success'));
    if (!error) {
        bleno.setServices([
                new bleno.PrimaryService({
                    uuid : myId,
                    characteristics : [
                            // add characteristics here
                            terminal
                    ]
                })
        ]);
        console.log('service added');
    }
});

bleno.on('accept', function(clientAddress) {
    console.log("Accepted connection from: " + clientAddress);
});

bleno.on('disconnect', function(clientAddress) {
    console.log("Disconnected from: " + clientAddress);
});

Since you haven't posted anything you've tried or researched, I would recommend you give it an attempt first and then post questions based on what you have attempted yourself.