Real time sensing with bluetooth smart

Real-time Sensing with
Bluetooth Smart
Tue Haste Andersen @tuehaste
Better Embedded, Florence #bem2013
9 JULY 2013

FROG IS A GLOBAL
PRODUCT STRATEGY
& DESIGN FIRM

Typically a system based on a microprocessor contained within another system.
The other system can be anything from a bigger computer, appliances like a fridge or oven, or even the human body.

HARDWARE
+
SOFTWARE
Thus embedded is hardward + a simple software system to manage the
hardware

HARDWARE
+
SOFTWARE
+
DATA
It is increasingly difﬁcult to imagine a self-contained system that does not interact with the outside world.
An embedded system increasingly needs to interact with the external world though a user or network interface.
Thus to the deﬁnition, we need to add “data”.

About a year ago...
About a year ago I was doing a race in a club for radio controlled “Mini Z” cars in Milan. The “Mini Z” cars are cars at a scale 1/28 produced by
Kyosho and are becoming increasingly popular.

80 meters
8 seconds
~ 36 km/h
The cars travel at a very high speed and are difﬁcult to control. Unfortunately I’m not really got at controlling the cars and start thinking about
ways to get better.
I decided to start measuring the cars using sensors and thereby improve my driving.

Does the chassis ﬂex?
Interesting parameters include temperature, force/ﬂexing of the chassis, energy, acceleration and speed.

How are my plants doing?
Once having a sensor system, it could be used not only to pull telemetic information from cars, but e.g. to monitor plant growth by tracking
sunlight and humidity.

Body sensing and User Research
... or sensors could be used in body tracking as we are doing at frog as part of the user
research.

I NEEDED SOMETHING:
- REALLY SMALL
- ROBUST
- CHEAP
- TO COLLECT DATA
To monitor radio controlled cars I needed something really small, since the cars a very sensitive to physical changes, it needs to be robust and
able to operate in an environment where radio signals are heavily used, it needs to be cheap and able to collect data.

BLUETOOTH
For this project I’ve chosen
Bluetooth.

BLUETOOTH
But why Bluetooth? Bluetooth is known to have serious problems with usability where it is both slow and cumbersome to pair two devices.

BLUETOOTH
Even simple operations like attaching a phone or a mouse to a computer often result in errors.

BLUETOOTH
The reason for choosing Bluetooth is because of the new protocol, Bluetooth Smart, that is included in Bluetooth 4.0.
Bluetooth Smart is a protocol originally developed by Nokia, and later integrated in the Bluetooth spec. Bluetooth Smart was originally called
Wibree and later Bluetooth Low Energy.
The main goal of Bluetooth Smart is to create a protocol with very low energy consumption and low latency.

PC SUPPORT 1 1 0 0 4 4
PHONE
SUPPORT
1 1 1 0 4 4
ATTENTION
FREE
PAIRING
4 4 4 4 1 4
MAX ACTUAL
THROUGHP.
200 kbps 424 kbps 20 kbps 250 kbps 6 Mbps 305 kbps
LATENCY 25 ms 1 s * 0 * 20-30 ms 1,5 ms * 2,5 ms
RANGE 1 m 5 cm ~10 m 300 m 150 m 50 m
PEAK
CONSUMP.
10 mA 50 mA * 17 mA 40 mA 116 mA 16 mA
NETWORK
TOPOLOGY
STAR STAR MESH, STAR MESH, STAR STAR STAR
IrDA NFC WiFi BluetoothANT+ ZigBee
COMPARING WIRELESS TECHNOLOGIES
This is a comparison of different wireless technologies. The peak consumption is a key factor for making a system
that can last long on a single battery. A rule of thumb is that the current draw should not be above the range of
15 mA to avoid damaging the battery (this is valid for the standard coin cell batteries, CR2032)

BLUETOOTH
“Google’s support for the
Bluetooth Smart Ready platform
in Android is one step forward for
Bluetooth’s dominance in the
internet of things.”
GIGAOM
Google announced on Google I/O 2013 support for Bluetooth 4.0 as of Android API v18

BLUETOOTH
“Bluetooth is not becoming the
de facto standard for your
personal area network… it already
is the standard for your personal
area network”
Bluetooth SIG
Bluetooth 4.0 is backed by more than 400 companies.

Bluetooth Smart devices are marketed using two labels.

Peripheral
Central
A peripheral only needs to implement functionality to advertise itself and participate in a
connection, but does not need the functionality to initiate a connection. A central on the
other hand needs to implement all the functionality of a peripheral + ability to initiate a
connect + support for all older standards of Bluetooth.

Peripheral Slave
Central Master
Data
The naming Slave and Master is also used in the specs.

Peripheral Slave
Peripheral
Central Master
Slave
A Bluetooth Smart Ready device can act both as a Central and as a Peripheral.

Bluetooth 4.0 Stack
Application
Generic Access Proﬁle
(GAP)
Generic Attribute
Proﬁle (GATT)
Attribute Protocol
(ATT)
Security Manager (SM)
Logical Link Control and Adaption Protocol
Link and RF layer

Bluetooth 4.0 Stack
Application
Generic Access Proﬁle
(GAP)
Generic Attribute
Proﬁle (GATT)
Attribute Protocol
(ATT)
Security Manager (SM)
Logical Link Control and Adaption Protocol
Link and RF layer
The parts of the stack that an application typically interfaces with are GAP and
GATT.

Central
Peripheral
Ad
Advertisement interval
(20ms to 10s)
Ad
(20ms to 10s)
Ad
(20ms to 10s)
Advertisement
A Bluetooth connection begins with the peripheral sending out advertisements to announce it’s presence. The advertisement interval can be
conﬁgured at the application level.

Central
Peripheral
Ad
(20ms to 10s)
Ad
(20ms to 10s)
Ad
(20ms to 10s)
Scanning Scanning
Advertisement
Scanning
A central is scanning for
advertisements.

Central
Peripheral Ad
Ch 37
(20ms to 10s)
Ad
Ch 37
(20ms to 10s)
Ad
Ch 37
(20ms to 10s)
Ad
Ch 38
Ad
Ch 39
Ad
Ch 38
Ad
Ch 39
Ad
Ch 38
Ad
Ch 39
Scanning Scanning
Advertisement
Scanning
Bluetooth 4 is using 40 different channels in the 2,4GHz spectrum. In reality 3 is used for advertisements and the remaining 37 is used when
the connection is established. Frequency hopping is implemented to ensure a stable connection.

Central
Peripheral Ad
Ch 37
(20ms to 10s)
Ad
Ch 37
(20ms to 10s)
Ad
Ch 37
(20ms to 10s)
Ad
Ch 38
Ad
Ch 39
Ad
Ch 38
Ad
Ch 39
Ad
Ch 38
Ad
Ch 39
Scanning Channel 39 Scanning Channel 37
Advertisement
Scanning Channel 38

Master
Central
Slave
Peripheral
Conn.
Req
150us
Data
Data
150us
Data
Data
Data
Data
150us 150us
Connection interval
(7.5ms to 4s)
Connection interval
(7.5ms to 4s)
Connection Interval
Once the central has initiated the connection, packets are exchanged between the central and peripheral at a ﬁxed interval, called
“connenction interval”. The connection interval is conﬁgurable at the application level. More data packets can be sent during the connection
interval.

Req. Data
Data
Data
Connection
interval
Connection
interval
Slave Latency = 2
Data
Connection
interval
Data
Data
Slave Latency
Master
Central
Slave
Peripheral
The peripheral is not required to respond to each packet. It is allowed to skip a number of packets deﬁned as the “slave latency”. In this ﬁgure
the slave latency is set to 2.
The slave latency is a value from 0 to 499, however, the maximum period that the peripheral remain silent should not exceed 16 seconds.

Mobile
Phone
Sensor
Bluetooth
Smart
The architecture that I’m following is based on a simple setup where sensors are attached electronically to the Bluetooth Peripheral, and the
peripheral communicates using Bluetooth Smart to a mobile phone.

Mobile
Phone
Sensor
Bluetooth
Smart
?

Temperature
Force
Accelerometer
Any sensors can be used. Good sources for ﬁnding useful sensors include Arduino and websites like Adafruit.

Analog
I²C
SPI
Sensors can be attached using either an ADC converter or through a serial protocol like Inter-Intergreated Circuit or Serial Peripheral Interface.

Texas Instruments
Nordic Semiconductor
CSR
EM Microelectronic
A number of manufacturers are producing Bluetooth Smart
chipsets.

Texas Instruments - CC2540/CC2541
Nordic Semiconductor
CSR
EM Microelectronic
Texas Instruments is producing the CC2540 chip that is interesting because it include a 8501 MCU, thus eliminating the need for an external
MCU. This reduces the total energy consumption and the complexity of the hardware design.

This is the architecture of the CC2540. The CC2541 is slightly different in that it includes a I2C hardware interface and no USB interface. The
CC2541 also consumes less energy.
To make the system run is also needed a crystal, antenna, signal cap, EEPROM etc. The total BOM (Bill of Materials) cost is around 3€.

Turnkey modules:
Bluegiga BLE112 and BLE113
Blueradio BR-LE4.0-S2A
Alpwise ALPW-BLEDVK002
Alpha Micro
Building a module around a chipset also requires a certiﬁcation from Bluetooth. An alternative is to use a turnkey module. Some options
include:
Bluegiga: http://www.bluegiga.com/BLE113_Bluetooth_Smart_module
Blueradio: http://www.blueradios.com/hardware_LE4.0-S2.htm
Alpwise: http://www.alpwise.com/produit.php?ref=ALPW-BLEDK002&id_rubrique=6
Alpha Micro: http://news.cision.com/livewire-pr/r/alpha-micro-launches-low-energy-bluetooth-smart--modules-for-medical-and-other-devices-
from-laird-te,c9405289

BlueGiga is a module with good documentation, it’s based on CC2540/CC2541
BgScripting language or BG API
According to BlueGiga it will be possible to use the IAR Workbench (expensive) 8051 compiler in the near future.
BLE112 costs around €11

Phones and computers
supporting BT4
iOS
Android
Linux
iOS (from iPhone 4S) has good support for BT4. Google has announced support in Android and Linux has support.

http://www.inmojo.com/store/jeﬀ-rowberg/item/ble112-
bluetooth-low-energy-breakout/
Building a hardware prototype requires the use of a development kit or the use of a breakout board. Breakout boards for BlueGiga are
available under the Creative Commons license.

After some Surface Mount Soldering, this is how the working prototype module looks
like...

Force
Sensor
Temperature
Sensor
Sensors can be attached to the ports similar to how sensors are attached to an
Arduino.

BGScript compiler from
http://techforum.bluegiga.com

Texas Instruments
CC Debugger
The CC Debugger costs around €50.

Flash programmer from
http://www.ti.com/tool/ﬂash-
programmer
As an alternative the open source cc-tool can be
used.

BGScript
Basic-like language
Event driven
No functions (!)
BGScript used to program the BLE112/3 modules is a basic like language, event driven, not allowing any functions to be deﬁned.

Generic Attribute Profile (GATT)
The first step in programming the firmware is defining a GATT
profile.

value
Byte array, from 0 to 512 bytes
Each type of value transferred can be a value between 0 and 512 bytes
long.

Characteristics specification at:
http://developer.bluetooth.org/
valuetype
16 bit predefined UUID
or
128 bit generated UUID
Each value is assigned to a type. The type can either be a type defined in the Bluetooth spec (16 bit UUID) or be a randomly generated 128
but UUID. This means that the application developer can define custom application-specific types and does not need to rely on the availability
of profiles in the chipsets and drivers. This is a really powerful feature of the new Bluetooth protocol.

valuetypehandle
16 bit handle
In addition a handle, an ID is assigned.

valuetypehandle permission
And various permissions.

Characteristic valuetypehandle permission
All these attributes are collectively called a Characteristic.

Service
A characteristic is assigned to a service.

Server
Service
A service to a server. The server is typically implemented by the
peripheral.

Service
Service
Server
A server can have more than one
service.

Service
Characteristic
valuetypehandle permission
Server
Service
A service can have more than one
characteristic.

Defining a GATT profile
The Gatt profile is defined in a simple XML
file.

Defining a GATT profile
A custom service and characteristic is defined with a generated
UUID.

Programming BLE113
BGScript is event driven. When the peripheral is powered on a system_boot event is raised. At this point the advertisement interval is
conﬁgured and advertisement is started.

Programming BLE113
Once a connection has been established a sensor is montiored using a timer. An analog sensor is read using a call to hardware_adc_read,
the result is not immediately available but given in another event.

Programming BLE113
The result is given as part of the hardware_adc_result_event. Here we write the value to the GATT database using the id “xgatt_force” that we
deﬁned in the GATT XML ﬁle.

iOS App using
CoreBluetooth and
AFNetworking.
Bluetooth connection
is kept alive while the
app is sleeping
The Bluetooth peripheral is connecting to an iPhone app. I’ve used Apple’s CoreBluetooth API and AFNetworking to relay the data to a cloud
service.

Issues
Each line of BGScript takes 1-3ms to execute
Problem with I2C
(hardware support in BLE113)
Changing GATT profile requires switching
Bluetooth off and on in iOS
1. The main issue with the BLE112/113 system is that BGScript is slow. It is not possible to measure sensor with high frequency with this
system. Instead a C compiler should be used.
2. On the CC2540/BLE112, the I2C interface is implemented in software making it slow and buggy. If you need I2C you should use CC2541/
BLE113.
3. When updating the GATT profile on the peripheral iOS does not see the changes. To account for this, switch off and on Bluetooth in iOS
settings

Actual Performance
Actual range around 25 meters
Duration on a standard CR2032 battery, with
constant non-optimized communication and
reading of four ADC sensors: around 4 hours
From a few experiments I’ve seen that the connection becomes somewhat unstable above 25 meters range. This obviously depends a lot on
the environment. Below 25 the connection is very stable, even in environments with a lot of radios in the 2,4GHz band.
The coin cell battery can last for a very long time, however, this requires setting the connection interval parameters rather conservative,
implement low power modes etc. etc. Running the chip in a busy loop where it reads the ADC and sends the values to the central, the battery
lasts for around 4 hours.

Sensor
Bluetooth
Peripheral
Phone
Sensors are connected with the phone using this
diagram.

Bluetooth 4analog/serialSensor
Bluetooth
Peripheral
Phone

Bluetooth
Peripheral
Phone
Desktop
Bluetooth
4
Desktop computers could be
used.

Bluetooth
Peripheral
Phone
Desktop
Bluetooth
4
Raspberry
Pi
Bluetooth 4
Or a Raspberry
Pi.

Bluetooth
Peripheral
Phone
Desktop
Bluetooth
4.0
Raspberry
Pi
Bluetooth 4.0
CloudTCP/IP
In any case the data needs to move off the device, to the cloud, to be able to share, compare and analyze the
data.

nodejs and log.io
The ﬁrst step is to setup a tool that allows to verify that the whole chain, from Sensor to cloud is working. For this I use the node.js program
log.io.
This is a simple tool that allows to see logs realtime in a web browser.

Sensing in the Cloud
Xively,
Open Sen.se,
SenseOS,
Etherios,
ElectricCimp,
One of the most mature cloud based sensor platforms is Xively (previously
Pachube)

Store Process Visualize
HTTPEvent
HTTP
Open Sen.se Cloud Platform
Open Sen.se offers a platform that is modular and easy to conﬁgure. The platform is still in private beta, but conceptually very
interesting.

Here’s an example of the force sensor data from the MiniZ car shown on Open
Sen.se.

Bluetooth Smart in a year:
Open Source breakout boards
Android Support
Improved iOS support
TI SmartTag developer kit
Lower power chipsets
Hundreds of devices launched

Bluetooth and Embedded is
clearly becoming easier, less
hardware hacking is needed
grazie a tutto cio, e’ diventato piu facile ad utilizare e programmare embedded e bluetooth
4

Bluetooth 4 is the standard
that will enable massive data
collection. A great challenge
lies in what to do with the
data.
Secondo me la prossima sﬁda e’ scoprire come sfruttare al meglio tutti questi
dati

Real time sensing with bluetooth smart

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