Bluetooth Low Energy / Mbed 2 deprecated BLE_URIBeacon

The Uniform Resource Identifier Beacon (UriBeacon) defines Bluetooth 4.0 Advertisement Data that contain Web URIs. URIBeacon provides a way for Bluetooth Low Energy devices to discover nearby URIs, for example, provides a way for a user to discover a short URL and then download it on their smartphone.

Dependencies:   BLE_API mbed nRF51822

Fork of BLE_PhysicalWeb by Bluetooth Low Energy

This example demonstrates how to set up and initialize a basic URI Beacon. For a more advanced example of using a URI beacon please see the BLE_PhysicalWeb project. The Google Github Page also gives a great description of what UriBeacons are and how to use them.

Basic Details

URI Beacons are a standard way of providing a URI link in a BLE advertising packet. Website URL's are the most popular URI's. The goal of URI Beacons are to act as a bridge between the physical and digital worlds. Since the URI can be any web capable link the possibilities for use are really endless. The UriBeacons can be thought of as a natural extension of and more useful version of QR codes.

Smartphone App Links

iPhone Physical Web app

Android App

Walkthrough of Physical Web application

Size of URI

The UriBeacon has one purpose, to advertise a web link. Because of the nature of BLE these web links have to be small. In order to provide a nice balance of small and useful the UriBeacon specification has abstracted out the representation of the URI prefix('http://www.', 'https://www.' , ...etc) and suffix ('.com','.org','.edu','.gov' ...etc) to a single byte each. Of the 27 bytes available for a usual BLE payload the UriBeacon has 19 bytes available for the URI. Of these 19bytes one byte must be given to the prefix. That leaves 18 bytes to fit the address and the suffix into. If the suffix used is not one of the standard ones in the UriBeacon specification then each letter will take up 1 byte instead of the entire suffix being abbreviated into a single byte.

Here are the acceptable abbreviations currently available

So for example the address "http://www.google.com" would take up 8 bytes. Both "http://www." and ".com" are supported abbreviations so each will be shortened to 1 byte.

An address like "http://www.bit.ly/xyz" would take up 11 bytes. Notice that ".ly" is not a supported suffix, so each letter takes up 1 byte.

Even addresses with the suffix in the middle are abbreviated, ie "http://www.youtube.com/XYZ". Notice here that the '.com' is in the middle of an address, it is still shortened to just 1 byte.

Using UriBeacons with mbed BLE API

Using the UriBeacon with the mbed API is rather simple. Just like any other BLE project you must first initialize the BLE baselayer by creating a ble object.

BLEDevice ble;

Then you pass the BLE object to a UriBeacon config service.

URIBeaconConfigService *uriBeaconConfig;
uriBeaconConfig = new URIBeaconConfigService(ble, "http://www.mbed.org");

Optionally you can then adjust settings of the UriBeacon such as transmission power levels, grabbing verbose debug information and other handy dandy services.

/* Adjust the TX Power Level */
    const int8_t powerLevels[] = {-20, -4, 0, 10};
    uriBeaconConfig->setTxPowerLevels(powerLevels); // Set TX power levels, Lowest(-20), Low(-4), Medium(0), High(10)
    uriBeaconConfig->setTxPowerMode(URIBeaconConfigService::TX_POWER_MODE_LOW); // Set transmission in Low power mode

/* Adjust Beacon Period*/
setBeaconPeriod(1000); // Set beacon to advertise every 1000ms

Other UriBeacon Services

This is just the bare basics of how URI beacons work. There is also a configuration service that allows URI beacons to be updated, locked, and provides other management feature. That is beyond the scope of this example but details can be found in the Technical Details section below.

Technical Details

For more details on how URI beacons work please see these websites:
UriBeacon Github Project : the github home for all things UriBeacon (maintained by google)
UriBeacon Specification : lots of good technical details
UriBeacon configuration service - This is a service that pairs with the UriBeacon that allows changing the URI's, locking them, and some other cool features. This service is not detailed in this example application.
Android App : smartphone application to view nearby UriBeacons.
iOS App : Sample code for using UriBeacons with iOS.
The PhysicalWeb Project : a project that the UriBeacon is central to.

In case you're really interested here is a diagram that nicely sums up how the 27bytes of advertising data payload are used.

/* mbed Microcontroller Library
 * Copyright (c) 2006-2015 ARM Limited
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "pstorage.h"
#include "nrf_error.h"
#include "ConfigParamsPersistence.h"

static pstorage_handle_t pstorageHandle;

/* Dummy callback handler needed by Nordic's pstorage module. */
static void pstorageNotificationCallback(pstorage_handle_t *p_handle,
                                  uint8_t            op_code,
                                  uint32_t           result,
                                  uint8_t *          p_data,
                                  uint32_t           data_len)
{
    /* APP_ERROR_CHECK(result); */
}

/* Platform-specific implementation for persistence on the nRF5x. Based on the
 * pstorage module provided by the Nordic SDK. */
void loadURIBeaconConfigParams(URIBeaconConfigService::Params_t *paramsP)
{
    pstorage_init();
    static pstorage_module_param_t pstorageParams = {
        .cb          = pstorageNotificationCallback,
        .block_size  = sizeof(URIBeaconConfigService::Params_t),
        .block_count = 1
    };

    pstorage_register(&pstorageParams, &pstorageHandle);
    if (pstorage_load(reinterpret_cast<uint8_t *>(paramsP), &pstorageHandle, sizeof(URIBeaconConfigService::Params_t), 0) != NRF_SUCCESS) {
        // On failure zero out and let the service reset to defaults
        memset(paramsP, 0, sizeof(URIBeaconConfigService::Params_t));
    }
}

/* Platform-specific implementation for persistence on the nRF5x. Based on the
 * pstorage module provided by the Nordic SDK. */
void saveURIBeaconConfigParams(URIBeaconConfigService::Params_t *paramsP)
{
    if (paramsP->persistenceSignature != URIBeaconConfigService::Params_t::MAGIC) {
        paramsP->persistenceSignature = URIBeaconConfigService::Params_t::MAGIC;
        pstorage_store(&pstorageHandle,
                       reinterpret_cast<uint8_t *>(paramsP),
                       sizeof(URIBeaconConfigService::Params_t),
                       0 /* offset */);
    } else {
        pstorage_update(&pstorageHandle,
                        reinterpret_cast<uint8_t *>(paramsP),
                        sizeof(URIBeaconConfigService::Params_t),
                        0 /* offset */);
    }
}