Bluetooth Low Energy / Mbed 2 deprecated BLE_iBeacon Featured

Beacon demo for the BLE API using the nRF51822 native mode drivers

Dependencies:   BLE_API mbed nRF51822 X_NUCLEO_IDB0XA1

Introduction

Bluetooth Low Energy Beacons are a service that allow for highly localized positioning. The Beacon service is particularly useful for indoor positioning, low power positioning and location aware software. A particular use of the Beacon service is iBeacon. The iBeacon standard is a Apple specific implementation of Beacons.

The Basics

The Beacon service is a BLE Service that operates in advertising mode only. A Beacon service advertises 4 things:

  • A company ID
  • A unique UUID (unique to a retailer)
  • A Major number (ex a store number)
  • A Minor number (ex a location in the store)
  • Signal Strength at transmitter (requires calibration per each device)

These pieces of information are all you need for a Beacon service to work. The majority of the heavy lifting is done by the smart phone application that reads these four fields and then uses a web app or a database of some sort to turn these numbers into valuable information about what you are near and how near you are to it.

The signal strength field is compared to the actual signal strength at the receiver to determine how close the beacon is to the phone. The number used is the calibrated signal strength 1 meter from the device. By doing this 1 meter increments can be used to measure distance from the Beacon. The distances usually get broken down into 3 ranges:

  • Immediate: Within a few centimeters
  • Near: Within a couple of meters
  • Far: Greater than 10 meters away

Company ID's are used to make beacon UUID's unique to companies. Some example company UUID's are:

  • 0x004C - Apple Inc.
  • 0x0059 - Nordic Semiconductor
  • 0x0078 - Nike
  • ​0x015D - Estimote
  • ​0x0171 - Amazon Fulfillment Service
  • 0xFFFF - reserved for internal testing before release

Here is the Bluetooth SIG's full list of Company ID's.

Example : Coffee Shop X

For example, if a smartphone app reads a BLE Beacon with UUID = 0x1234546... , Major Number=5, Minor number = 3, it would check that against a database. From that database it would find out that UUID 0x123456... is owned by Coffee Shop X, that Major number 5 belongs to the store on main street and that Minor number 3 belongs to the coffee rack in that store. Then the application could check to see if there are any deals for the Coffee Shop X on Main Street on Coffee today. If there are any deals the phone could then alert the user and display a coupon code.

Example : museum

The Beacon service also provides a way for the phone to tell how close it is to the beacon. This can be useful for location aware applications, such as in a museum. For example, the smartphone reads a BLE Beacon with UUID = 0x98765....., Major Number=1, minor number = 0. The smartphone then looks this up in a database and find the UUID is for the Natural Science Museum, Major Number 1 = the Art Gallery room 1, and the minor number 0 = an abstract painting of a duck. If we assume all the paintings are spread out at 10feet each, then the application can sense when you are within 3 feet of the painting (based on signal strength of the Beacon) and give the user information about the painting they are approaching.

Technical Details

An iBeacon is just a normal Bluetooth LE device broadcasting advertisements with special data shoved into the Manufacturer Specific Data field.

The iBeacon prefix is little more than metadata about the advertisement packet.

BytesDatadescription
0,1,20x020106This sets the flags for General Discoverable and BR/EDR not supported
3,40x1AFFThis says the length of the Manufacturer specific data field will be 26 bytes
0,10x4C00Company ID
20x02ID
30x15length of remaining data in bytes (16B UUID+ 2B major, 2B minor, 1B Txpower)

Note that bytes 0-4 are set implicitly by the API by declaring the advertising data to be LE General Discoverable and BR/EDR not supported. The remaining fields that make up an iBeacon advertisement packet can be clearly seen in the image below.

http://www.havlena.net/wp-content/uploads/ibeacon-packet.png

For a more depth explanation please see these well done explanations:

main.cpp@60:3034dc913ea1, 2015-03-24 (annotated)

Committer:
rgrover1
Date:
Tue Mar 24 08:08:38 2015 +0000
Revision:
60:3034dc913ea1
Parent:
59:4cd4f48e2775
Child:
69:f121dba6fcd3
updating underlying libraries.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
ktownsend 0:7613d21e5974 1 /* mbed Microcontroller Library
ktownsend 0:7613d21e5974 2 * Copyright (c) 2006-2013 ARM Limited
ktownsend 0:7613d21e5974 3 *
ktownsend 0:7613d21e5974 4 * Licensed under the Apache License, Version 2.0 (the "License");
ktownsend 0:7613d21e5974 5 * you may not use this file except in compliance with the License.
ktownsend 0:7613d21e5974 6 * You may obtain a copy of the License at
ktownsend 0:7613d21e5974 7 *
ktownsend 0:7613d21e5974 8 * http://www.apache.org/licenses/LICENSE-2.0
ktownsend 0:7613d21e5974 9 *
ktownsend 0:7613d21e5974 10 * Unless required by applicable law or agreed to in writing, software
ktownsend 0:7613d21e5974 11 * distributed under the License is distributed on an "AS IS" BASIS,
ktownsend 0:7613d21e5974 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
ktownsend 0:7613d21e5974 13 * See the License for the specific language governing permissions and
ktownsend 0:7613d21e5974 14 * limitations under the License.
ktownsend 0:7613d21e5974 15 */
ktownsend 0:7613d21e5974 16
ktownsend 0:7613d21e5974 17 #include "mbed.h"
mbedAustin 53:f9ec2c7a47f5 18 #include "iBeaconService.h"
ktownsend 0:7613d21e5974 19
mbedAustin 56:56bc0cab3916 20 /**
mbedAustin 56:56bc0cab3916 21 * For this demo application, populate the beacon advertisement payload
mbedAustin 56:56bc0cab3916 22 * with 2 AD structures: FLAG and MSD (manufacturer specific data).
mbedAustin 56:56bc0cab3916 23 *
mbedAustin 56:56bc0cab3916 24 * Reference:
mbedAustin 56:56bc0cab3916 25 * Bluetooth Core Specification 4.0 (Vol. 3), Part C, Section 11, 18
mbedAustin 56:56bc0cab3916 26 */
mbedAustin 56:56bc0cab3916 27
mbedAustin 50:7bc38f01d2d3 28 BLEDevice ble;
mbedAustin 50:7bc38f01d2d3 29
mbedAustin 56:56bc0cab3916 30 /**
mbedAustin 56:56bc0cab3916 31 * The Beacon payload has the following composition:
mbedAustin 56:56bc0cab3916 32 * 128-Bit / 16byte UUID = E2 0A 39 F4 73 F5 4B C4 A1 2F 17 D1 AD 07 A9 61
mbedAustin 56:56bc0cab3916 33 * Major/Minor = 0x1122 / 0x3344
mbedAustin 56:56bc0cab3916 34 * Tx Power = 0xC8 = 200, 2's compliment is 256-200 = (-56dB)
mbedAustin 56:56bc0cab3916 35 *
mbedAustin 56:56bc0cab3916 36 * Note: please remember to calibrate your beacons
mbedAustin 56:56bc0cab3916 37 * TX Power for more accurate results.
mbedAustin 56:56bc0cab3916 38 */
rgrover1 57:9782cb35c494 39 const uint8_t uuid[] = {0xE2, 0x0A, 0x39, 0xF4, 0x73, 0xF5, 0x4B, 0xC4,
rgrover1 57:9782cb35c494 40 0xA1, 0x2F, 0x17, 0xD1, 0xAD, 0x07, 0xA9, 0x61
rgrover1 57:9782cb35c494 41 };
mbedAustin 56:56bc0cab3916 42 uint16_t majorNumber = 1122;
mbedAustin 56:56bc0cab3916 43 uint16_t minorNumber = 3344;
mbedAustin 56:56bc0cab3916 44 uint16_t txPower = 0xC8;
mbedAustin 56:56bc0cab3916 45
ktownsend 0:7613d21e5974 46 int main(void)
ktownsend 0:7613d21e5974 47 {
Rohit Grover 11:6774f4827024 48 ble.init();
mbedAustin 53:f9ec2c7a47f5 49
mbedAustin 56:56bc0cab3916 50 iBeaconService ibeacon(ble, uuid, majorNumber, minorNumber, txPower);
mbedAustin 53:f9ec2c7a47f5 51
rgrover1 60:3034dc913ea1 52 ble.setAdvertisingInterval(1000); /* 1000ms. */
Rohit Grover 19:869d8c7306b4 53 ble.startAdvertising();
ktownsend 0:7613d21e5974 54
mbedAustin 56:56bc0cab3916 55 while(1) {
mbedAustin 56:56bc0cab3916 56 ble.waitForEvent(); // allows or low power operation
ktownsend 0:7613d21e5974 57 }
Rohit Grover 10:391c1acf4b9d 58 }