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Microcontrollers: Lecture 7 Wireless Sensor Networks, Sensors and

radio Interfaces, Projects, Exercises.

Michele Magno

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Calendar

07.04.2017: Power consumption; Low power States; Buses, Memory, GPIOs

20.04.2017 Serial Communications

21.04.2017 Programming STM32

27.04.2017 Interrupts, Timers

Exercises

28.04.2017 Programming STM32

04.05.2017 Sensors, ADC and DMA

05.05.2017 Sensors / Radios / short seminar on WSN

Projects presentation and exercises summary.

Sensors

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Sensing is a Must

4Departement Informationstechnologie und

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Digital MEMS block schematic

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…open the datasheet

You will find a Table with PIN description

Block diagramshowing that thereis more than the micro-mechanicalelement

Indication of referencedirections of the 3 accelerations

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Check the electrical characteristics

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Interfacing with uC

The LIS3LV02DL (STMicroelectronics) can be accessed through both the

I2C and SPI serial interfaces. The latter may be SW configured to operate

either in 3-wire or 4-wire interface mode.

The serial interfaces are mapped onto the same pads

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Digital Output – I2C Interface- Adapted voltage- Logic level

determined by Vdd- More sensors- Slower

… connect to uC (1)

Communication occurs trough data bus

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Digital Output – SPI Interface- monodirectional lines- faster- transm freq = uc clk

… connect to uC (2)

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Sensor

… connect to uC (3) – analog MEMS

Amplifier MicrocontrollerFilter

1212

All the building blocks

Wireless Communication

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WSN Protocols

WSN protocol strongly impact on system performance

Choosing the wrong protocol may cause severe inefficiency and prevent the WSN to accomplish user need.

The protocol affect:

Energy dissipation

System cost

Latency

Security

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Radio interface

SPI DATA I/O

TIMER MCU RADIO

ANTENNARADIO SUBSTYSTEM

Radio only performs modulation‐demodulation

SPI serial port for data interface

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Radio Subsystem

• Ease of communication with other devices

• Consumption (10 - 100mA)

• Start-up time and available bandwidth

Transceiver

• Chip antenna

• PCB antenna

• External antenna

Antenna

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Radio subsystem architecure

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Radio module stand alone

FEATURES:

Integrated chip antenna

& crystal

Easy to connect

Ready to use

Internal MCU

Stack protocol on board

Flexible

Internal Flash

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Radio module interface

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Wireless microcontroller

Benefits

Single chip integrates transceiver and microcontroller for wireless sensor networks

Cost sensitive ROM/RAM architecture, meets needs for volume application

System BOM is low in component count and cost

Hardware MAC ensures low power consumption and low processor overhead

Extensive user peripherals

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Protocol layers

Protocols specific

User specific

User application, usually, are built over Network layer

WSN protocols define lower levels

Physical

Data Link (MAC)

Network

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Physical layer

Provides mechanical, electrical, functional, and procedural characteristics to establish, maintain, and release physical connections (e.g. data circuits) between data link entities

Communication bands and number of channels

Spreading and Modulation

Data Rate

Cost – Power consumption – Reactiveness

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Physical layer

Communication bands and number of channels

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Physical layer

Spreading and Modulation

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Physical layer

Data Rate

20, 40, 250 kbps

1, 3 Mbps

54 Mbps

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Classification of communication networks

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Data link layer (MAC)

Physical

Network

Data LinkMAC Protocol

Layer 2

Layer 3

Layer 1

OSI

Data link layer: Mapping network packets

radio frames

Transmission and reception of frames over the air

Error control Security

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Data link layer (MAC) (2)

Control access to the shared medium

Avoid interference and mitigate effects of collisions

A B C

A B C D

Hidden terminal problem

Exposed terminal problem

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Energy efficient MAC

idle listening (to handle potentially incoming messages)

collisions (wasted resources at sender and receivers)

overhearing (communication between neighbors)

protocol overhead (headers and signaling)

traffic fluctuations (overprovisioning and/or collapse)

scalability/mobility (additional provisions)

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Network layer

Provides functional and procedural means to exchange network service data units between two transport entities over a network connection. It provides transport entities with independence from routing and switching consideration

Organization of the network Network formation

Joining/leaving the network

Routing of packets through the network Shortest path

Energy efficient

Tracing of the status of the links Routing tables

On demand path (e.g. AODV)

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Network – Structure

Not always predictable but can follow logical structure

Mesh Cluster tree

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Network – Structure

Not always predictable but can follow logical structure

Clustering:

Balance load among nodes Cluster Head must compute more data

energy efficency

Adapt to network changes

Reduce data transfer

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Network – Routing

Hard, due to node failure and mobility

Balance between low duty cycle and frequent path updates

Routing algorithm can be classified in three group

Connect dominating

Try to find the shorter path to the destination

Energy dominant

Life of network can be longer if energy consumption is balanced among nodes

Biological model

Ants communication paradigm

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Protocols – Security (1)

Security Concerns:

Integrity - Ensure that information is accurate, complete, and has not been altered in any way.

Availability - Ensure that a system can accurately perform it’s intended purpose and is accessible to those who are authorized to use it.

Confidentiality - Ensure that information is only disclosed to those who are authorized to see it.

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Protocols – Security (2)

Traditional security techniques cannot be applied due to system constraints

Power

Bandwidth

Computation

Secure protocols uses:

Encription

Data authentication

Data freshness

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Bluetooth:2.4GHZ

Frequency Hopping Spread Spectrum(1600 hop/s)

720kb/s up to 3Mb/s (for voice, audio and bulk data)

ZigBee:800 MHz, 900 MHz, 2.4GHz

Direct Sequence Spread Spectrum

250kb/s (Optimised for short packets)

Networking

Dynamic ad-hoc Pico-nets, master negotiation

Extensive profiles to ensure compatibility

Active / Park modes

Hybrid MAC (mostly scheduled, with RT streams)

Networking

Large master-slave networks, with fast access

Slave - initiated communication, (slave energy reduced)

Virtual peer-peer device pairing links

Hybrid MAC (mostly contention)

State transitionsNetwork join time 3s

Sleeping slave changing to active = 3s typ.

Active slave channel access time = 2ms typ.

State transitionsNetwork join time = 30ms typ

Sleeping slave changing to active = 15ms typ

Active slave channel access time = 15ms typ

ZigBee VS BT VS BTLE

BTLE (4.0):2.4GHZ

GFSK @ 2.4 GHz Adaptive Frequency Hopping

Sleep current ~ 1µA

1Mb/s (no optimized for files)

Networking

New ease of discovery & connection

Asynchronous connection-less MAC

Modes:Broadcast, Connection, Event Data Models Reads, Writes

State transitions3ms from start to finish with

Asynchronous

Sleeping slave AsynchronousClient / Server architecture

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ZigBee vs. BTLE

BTLE focuses on low power & low cost communications betweenmobile phones and small sensor devices,

Mobile phones will have several radios (many @ 2.4 GHz): BTLE iscost- and power-wise optimized for sensor connectivity in thisenvironment,

BTLE ~ZigBee in terms of peak power, but due to the higher bit rate, Wibree results in lower energy per bit @ high utilization

ZigBee focuses on home and industry automation.

Wibree does not support mesh networks as does ZigBee

ZigBee support higher range operation

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Power Consumption in WSN

0

2

4

6

8

10

12

14

16

Po

wer

(mW

)

Power Consumption

Sensing

Communication

Data processing

CPU Sensing TX RX Idle Sleep

RADIO

Usually the Radio is the most power hungry component

Idle mode is needed to allow the node to be reactive but it wastes a lot of power.

Sleep Mode consumption is very low.

• WSN Complex systems made up of a large number of sensor nodes.

Each node has:– Communication

– Sensing

– Computing

– Power (batteries, scavengers)

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Wake Up Radio Motivations

• Listening mode power consumption of wakeup radio much less than idle power consumption of standard radio

• Using information about traffic in the network, we can make better decisions about how frequently to wake up the microcontroller

Power Characteristics for a CC2520 transceiver

Radio wake

up

Main Radio

Sleep < uW 1 mA

TX/RX < uW 20 mA

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Wake up radio Concept

CPU

Main

Radio

ON/OFF

Wake up radio

receiver Interrupt

Wake up Message

Main RADIOTon

Wake up radio

receiver

Toff Toff

Wake up Message Always on nano power consumption

t

t

Sleep/wake up radio technique

Project EXAMPLE: Let’s build our smart

home!

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Projects: You can work and learn on hardware/firmware/software from the project.

HARDWARE:

Design PCB

Sensors Interfaces

Wake up Radio and Analog/Digital Desing

Energy Harvesting and Power Circuits

Software

Firmware for microcontrollers

Firmware to take data from sensors and processing on-board

Firmware and protocols for Radios

Software on application level to get information, processing data.

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Sensori

CPU

Head Up Display

Project Example: Smart Helmet

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44shelmet: sensors

3-axis Accelerometer

Temperature & Ambient Light Sensors

• Alcohol detection system

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Student projects can involve Hardware implementation and optimization

New PCB with hardware design.

Possible new sensors / LCD Display / Sensor network

Energy Harvesting and power stafges

Firmware implementation

MSP432 (ARM CORTEX M4F) programming

Data acquisition and low power classifier (with deep learning)

Wireless communication

Software power management

Software implementation on Android/iOS

App for data logging

Interfacing with the helmet

Data analysis, clouding, social network, GPS

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Exercises

We have two microcontrollers with the following

specifications

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MCU A

(1.8V to 3V)

MCU B

(1.5V to 3V)

Active mode200 µA@3V/MHz (up

8MHzMaster Clock)

300µA@3V/MHz(16MHz Master

Clock)

Active mode150 µA@2V/MHz (up to 2Mhz

Master Clock)

180 µA@2V(up to 4Mhz Master

Clock)

Sleep Mode 1.2 uA 0.6 uA

The microcontroller should be selected to be attached to a Analog sensor to

acquire a analog signal with frequency at 1KHz with a voltage range of 1V. The

required resolution for the ADC is of at least 550µV. For the sensor specification

the sample and hold period should be at least of 90µs.

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ADC Clock Diagram

ADCCLKPrescaler

/2, /4, /6 or /8

Master Clock

3 cycles

15 cycles

28 cycles

84 cycles

58 cycles

Sa

mp

leT

ime

Se

lec

tion

The ADC Block of the internal microcontroller

follows:

Goal:

• Configure the ADC to satisfy the project requirements

• Select the Microcontroller and configuration to satisfy the Project specification and consumes less energy

in continuous mode.

• Quantify the energy consumption

• Estimate the lifetime of a system (for both MCU A and MCU B) that acquires the sensor data every 4 hour

for 36s with a battery of 100mAh, and discuss the best on the best microcontroller.

• Design the block diagram of the system designed

Vref

3V

2V

1.5V

1.1V

Resolutions

12 bits

10 bits

8 bits

6 bits

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Solution: Configure the ADC

We need to understand

the minimal Frequency needed for the ADC sampling and acquisition.

Constrains:

- Sample and hold time of the sensor (90µ) –> It Will fix the SAMPLE AND HOLD time and the minimal ADC frequency.

- Minimal Resolution of 550µV. -> It will fix Vref and the ADC-bits

- Sample frequency for Nyquist (1KHz) –> It will fix the ADC Clock, and it will depend of the

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Solution ADC:

90µs -> 1/T => frequency of 11.11KHz of Sampling and hold.

We can select number of clock cycle of 3/15/28. Let’s select 15.

- This results on 166.66KHz of minimal clock ADCLK. NOTE IF YOU NEED A FASTER ADCLOCK YOU NEED TO GO FASTER! AND SELECT HIGHER SAMPLE&HOLD CYCLING.

ADCLK depends of Master clock of at least a prescale of /2 /4/6 etc.. Lets chose

6. So the minimal master clock is 1MHz to satisfy the sample and Hold.

550µV -> Sensor has 1V maximum value. We can choose 1.1 For the

reference. From:

With 11bits ADC -> 1.1V/211 = 530µV -> OK!

n

ref

LSB

VV

2

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For Nyquist we need to sample at the double of the frequency of the

signal that is at 1KHz -> so we need to sample at 2KHz.

So we need a conversion time less than 1/2KHz = 500µs.

TADC = Tsample + Tconversion Where Tconversion = Tclk*bits.

Tsample = 90us

Tconversion = 66us

TADC= 156us => Maximal frequency 6.4KHz. So we fit the SPECIFICATIONS

and also we could reduce the ADC clock if needed.

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First Selection to fit the ADC requirements.

Master Clock 1MHz

ADC Clock 166KHz (1MHz/6)

Exercise• Let’s assume we

• two possible microcontrollers as in

table.

• A battery of 100mAh a 3.7V.

• Evaluate the minimal Duty Cycling

that maximize the number of tasks

executed and achieve 2 weeks for

each Microcontroller assuming the

minimal time for the active task is

1s at 16MHz and 2s at 8MHz.

•

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05.05.2017Presentation Title

MCU A

(1.8V to 3V)

MCU B

(1.5V to

3V)

Active

mode2 mA (8Mhz)

3 mA

(16Mhz)

Low power

mode0.6 uA 1 uA

• EBattery = 100mAh * 3600s * 3.7V-> 1320J

• Etask = P * time ->

• MCU-A -> P = 2mA*1.8V ; Etask = 3.6mW * 2s = 7.2mJ

• MCU B-> P = 3mA * 1.5V; Etask = 4.5mW * 1s = 4.5mJ

• Theoretical Max Numbers tasks (no dissipation in sleep) : Ebattery / Etask

• MCU A -> 184000

• MCU B -> 296000

• Lifetime in Continuous mode[h]: Battery[mAh] / Current Consumption [h]

• MCU A -> 50 h

• MCU B -> 33 h (But double number of Tasks)

• Duty Cycling. D = P/T *100.

• Example MCU A => P = 2s , T = 10s -> D= 20%.

• Example MCU B=> P = 1s T= 10s -> D= 10%

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05.05.2017Presentation Title

Exercise

• ESleep = PLowPowerMode * Sleep time [T-Active Time] ->

• MCU-A -> P = 0.0006mA*1.8V = 3.6µW * 8s = 8.6µJ

• MCU B-> P = 0.001mA * 1.5V = 1.5µW * 9s = 13.5µJ

Exercise I

• Evaluate the life time using the following duty cycling

• MCU B: T= 1000s; P = 1s; D= ?

• MCU A: T = 2000s; P = 2s; D = ?

• Which one last more? How Long?

• Etot (T) = Esleep (T- P) + Etask (T)

• MCU_B => Etask = 4.5mJ ; Esleep = 1.5µW * 999s= 1.498mJ; Etot = 5.99mJ

• MCU_A => Etask = 7.2mJ ; Esleep = 3.6µW * 1998s = 7.19mJ; Etot = 14.49mJ

• LifeTime (s) = (Ebattery / Etot ) * T

• MCU_B => 7 Years!

• MCU_A => 6 years!

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05.05.2017Presentation Title

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How select the Microcontroller?

We need to evaluate the power/energy consumption with the previous

results

Power = Voltage * Current = [W]

Energy = P * time in seconds. = [J]

Energy duty cycling period T = Pactive*Tact + Psleep*Tsleep

T = Tact + Tsleep -> Duty Cycling D = Tact/T *100

In Continues mode D = 100% so Tsleep = 0

MCU A Power = 2V * 200µA (1MHz) = 400µW

MCU B Power = 2V * 300µA (1MHz) = 600µW! 33% MORE EXPENSIVE

Energy for one hour -> 1.44J for MCU A.

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Energy With Duty Cycling

In 4 hours the active mode it is only 36s.

T = 4h. Duty Cycling is 36s / 4h*3600 => 0.0025%

We need to evaluated Psleep

Psleep = Tsleep * Voltage * Isleep

Energy for sleep period

MCU A = 14364s * 2V * 1.2µA = 34.4mJ

MCU B = 14364s * 2V * 0.6µA = 17.2mJ

Energy for period T of 4h Esleep + Eactive

MCU A= 34.4mJ + 36*400µW = 48.8mJ

MCU B = 17.2mJ + 36*600 µW = 38.8mJ

MCU B IS MORE EFFICIENT!

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Estimation of Lifetime.

Assuming we have 100mAh without conversion losses (battery could works

of more than 2V and MCU works at 2V)

MCU A: Energy per hour -> 48.8mJ / 4 (h) -> 12.2mJ per 1h

MCU B: Energy per hour -> 48.8mJ / 4 (h) -> 9.7mJ per 1h

Average Power = Energy per hour/ 3600s =

=3.38µW (MCU A) and 2.69µW (MCU B)

Average Current MCUA = Power / Volt = 1.69µA

Average Current MCUB = Power / Volt = 1.34µA

Lifetime[years] = 100mAh /Avg. Current => around 6.5y MCUA and 8.5y

MCUB