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

WHAT IS EMBEDDED?

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+

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

PAIRING4 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 4.0

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

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

Peripheral Slave

Peripheral

Central MasterSlave

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

Bluetooth 4.0 StackApplication

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 StackApplication

Generic Access Profile(GAP)

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)

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

Scanning Scanning

Scanning

A central is scanning for advertisements.

Central

Peripheral AdCh 37

AdCh 37

AdCh 38

AdCh 39

AdCh 38

AdCh 39

AdCh 38

AdCh 39

Scanning Scanning

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 AdCh 37

AdCh 37

AdCh 38

AdCh 39

AdCh 38

AdCh 39

AdCh 38

AdCh 39

Scanning Channel 39 Scanning Channel 37

Scanning Channel 38

MasterCentral

SlavePeripheral

Conn.Req

150us 150us

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

Connection interval

Slave Latency = 2

Connection interval

Slave Latency

MasterCentral

SlavePeripheral

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.

MAKING

MobilePhoneSensor Bluetooth

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.

Smart?

Temperature

Accelerometer

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

Analog

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

Smart?

Texas Instruments

Nordic Semiconductor

EM Microelectronic

A number of manufacturers are producing Bluetooth Smart chipsets.

Texas Instruments - CC2540/CC2541

Nordic Semiconductor

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 BLE113Blueradio BR-LE4.0-S2AAlpwise ALPW-BLEDVK002Alpha 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_moduleBlueradio: http://www.blueradios.com/hardware_LE4.0-S2.htmAlpwise: http://www.alpwise.com/produit.php?ref=ALPW-BLEDK002&id_rubrique=6Alpha 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/CC2541BgScripting language or BG APIAccording to BlueGiga it will be possible to use the IAR Workbench (expensive) 8051 compiler in the near future.BLE112 costs around €11

Smart ?

Phones and computers supporting BT4

iOSAndroidLinux

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

HARDWARE PROTOTYPE

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.

FIRMWARE PROGRAMMING

YOU NEED 4 THINGS

Text editor

BGScript compiler fromhttp://techforum.bluegiga.com

Texas Instruments CC Debugger

The CC Debugger costs around €50.

Flash programmer fromhttp://www.ti.com/tool/flash-programmer

As an alternative the open source cc-tool can be used.

BGScript

Basic-like languageEvent drivenNo functions (!)

BGScript used to program the BLE112/3 modules is a basic like language, event driven, not allowing any functions to be defined.

The first step in programming the firmware is defining a GATT profile.

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 UUIDor

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

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.

SensorBluetoothPeripheral Phone

Sensors are connected with the phone using this diagram.

Bluetooth 4analog/serialSensorBluetoothPeripheral Phone

Desktop

Bluetooth

Desktop computers could be used.

Desktop

Bluetooth

RaspberryPi

Bluetooth 4

Or a Raspberry Pi.

Desktop

Bluetooth

RaspberryPi

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

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.

Conclusion

Bluetooth Smart in a year:

Open Source breakout boardsAndroid SupportImproved iOS supportTI SmartTag developer kitLower power chipsetsHundreds 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

Tweets on data, sensing and startups

@tuehaste

real time sensing with bluetooth smart

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