1 ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters Hardware Components:...

ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 1

Hardware Components:Sensors, Actuators,

Converters+

Nikil DuttUC Irvine

ICS 212 Winter 2005

+Copyrighted Material adapted from Peter Marwedel, Frank Vahid and Tony Givargis

Templates from Prabhat Mishra


Simplified Block Diagram

actuatorsactuators


Sensors and Actuators

Sensors: Capture physical stimulus (e.g.,

heat, light, sound, pressure, magnetism, or other mechanical motion)

Typical generate a proportional electrical current

May require analog interface

Actuators Convert a command to a physical

stimulus (e.g., heat, light, sound, pressure, magnetism, or other mechanical motion)


solenoid mic

laser diode/transistor

speaker

dc motor

compass

accelerometer


Sensors

Processing of physical data starts with capturing this data.

Sensors can be designed for virtually every physical stimulus

heat, light, sound, weight, velocity, acceleration, electrical current, voltage, pressure, ...

Many physical effects used for constructing sensors. law of induction (generation of voltages in an electric field), light-electric effects.


Example: Acceleration Sensor

Courtesy & ©: S. Bütgenbach, TU Braunschweig

MEMS device

Small mass in center

When accelerated: Mass displaced

from center Resistance of wires

connected to mass change

Detect change in resistance and model acceleration


Charge-coupled devices (CCD)

Image Sensors: Based on charge transfer to next pixel cellImage Sensors: Based on charge transfer to next pixel cell


CMOS Image Sensors

Based on standard production process for CMOS chips, allows integration with other components.


Comparison CCD/CMOS sensors

Sou

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B. D

ieric

ks: C

MO

S im

age

sens

or c

once

pts.

P

hoto

nics

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(Web

)


Example: Biometric Sensors

Example: Fingerprint sensor (© Siemens, VDE):Example: Fingerprint sensor (© Siemens, VDE):

Integrated into ID mouse.


Example: Artificial eyes

© Dobelle Institute(www.dobelle.com)


Artificial eyes (2)

He looks hale, hearty, and healthy — except for the wires. They run from the laptops into the signal processors, then out again and across the table and up into the air, flanking his face like curtains before disappearing into holes drilled through his skull. Since his hair is dark and the wires are black, it's hard to see the actual points of entry. From a distance the wires look like long ponytails.

© Dobelle Institute(www.dobelle.com)


Other examples of sensorsHeart monitoring sensors

“Managing Care Through the Air”» IEEE Spectrum Dec 2004

Rain sensors for wiper control High-end autos

Pressure sensors Touch pads/screens

Proximity sensors Collision avoidance

Engine control sensorsAudio sensors Motion sensorsThermal sensors

SARS detection (“high fever”)



actuatorsactuators



Sensors: Capture physical stimulus (e.g.,

heat, light, sound, pressure, magnetism, or other mechanical motion)

Typical generate a proportional electrical current


Actuators Convert a command to a physical

stimulus (e.g., heat, light, sound, pressure, magnetism, or other mechanical motion)


solenoid mic

laser diode/transistor

speaker

dc motor

compass

accelerometer


Actuators

Output physical stimulus varies in range and modality Large (industrial) control actuators

Pneumatic systems: physical motionOptical output

IRThermal outputSmall motor controllers (stepper motors)MEMS devicesList goes on…..


Stepper Motor Controller

Stepper motor: rotates fixed number of degrees when given a “step” signal In contrast, DC motor simply rotates when power applied,

and coasts to stop

Rotation achieved by applying specific voltage sequence to coils

Controller greatly simplifies this


MEMS Actuators

Huge variety of actuators and output devices.

Microsystems motors as examples (© MCNC)(Dimensions in the order of several microns)

(© MCNC)


Actuators

Courtesy and ©:E. Obermeier, MAT,

TU Berlin



actuatorsactuators


Sample-and-Hold Circuit

Sampling: how often the signal is converted.Quantization: how many bits used for sampling.

Model: Vx = Ve when Clock = 1


Aliasing

-1.5

-1

-0.5

0

0.5

1

1.5

Potential Consequence of sampling, e.g.:Signal frequency: 5.6 HzSampling frequency: 9 Hz


Analog to Digital Conversion

Sampling: how often is the signal converted?Twice as high as the highest frequency signal present in

the input

Quantization: how many bits used to represent a sample?Sufficient to provide required dynamic range Under-loading: dynamic range not used properlyClipping: input signal beyond the dynamic range

Aliasing: erroneous signals, not present in analog domain, but present in digital domainUse anti-aliasing filtersSample at higher than necessary rate


Analog-to-Digital Converter

proportionality

Vmax = 7.5V

0V

11111110

0000

0010

0100

0110

1000

1010

1100

0001

0011

0101

0111

1001

1011

1101

0.5V1.0V1.5V2.0V2.5V3.0V

3.5V4.0V4.5V5.0V

5.5V6.0V6.5V7.0V

analog to digital

4

3

2

1

t1 t2 t3 t4

0100 1000 0110 0101

time

analog input (V)

Digital output

digital to analog

4

3

2

1

0100 1000 0110 0101

t1 t2 t3 t4time

analog output (V)

Digital input


Flash A/D Converter

Parallel comparison with reference voltage Speed: O(1) HW complexity: O(n)

n= # of distinguished voltage levels


Successive Approximation

Key idea: binary search:Set MSB='1' if too large: reset MSBSet MSB-1='1'if too large: reset MSB-1 …..

Speed: O(log(n))Hardware complexity: O(log(n))with n= # of distinguishedvoltage levels;slow, but high precision possible.

Speed: O(log(n))Hardware complexity: O(log(n))with n= # of distinguishedvoltage levels;slow, but high precision possible.


Successive Approximation

Given an analog input signal whose voltage should range from 0 to 15 volts, and an 8-bit digital encoding, calculate the correct encoding for 5 volts.

0 1 0 0 0 0 0 0

½(Vmax – Vmin) = 7.5 voltsVmax = 7.5 volts.

½(7.5 + 0) = 3.75 voltsVmin = 3.75 volts.

0 0 0 0 0 0 0 0

0 1 0 0 0 0 0 0½(7.5 + 3.75) = 5.63 voltsVmax = 5.63 volts

½(5.63 + 3.75) = 4.69 voltsVmin = 4.69 volts.

0 1 0 1 0 0 0 0

½(5.63 + 4.69) = 5.16 voltsVmax = 5.16 volts.

0 1 0 1 0 0 0 0

½(5.16 + 4.69) = 4.93 voltsVmin = 4.93 volts.

0 1 0 1 0 1 0 0

½(5.16 + 4.93) = 5.05 voltsVmax = 5.05 volts.

0 1 0 1 0 1 0 0

½(5.05 + 4.93) = 4.99 volts 0 1 0 1 0 1 0 1


Signal Processing

Digital signal S0, S1, S2 … Sn-1

What can we do with it?Transpose: e.g., Zi = Si + KAmplify: e.g., Zi = Si Compose: e.g., Zi = (S1

i 1 + K1) + (S2i 2 + K2)

Filter: e.g, Zi = (Si+ Si+1) / 2Compress: e.g., using Huffman codesArchive, match against database, etc.

Or, process after converting to frequency domainSpectral analysis


Frequency Domain

Any continuous time varying signal can be represented as the sum of cosine functions of different amplitude and frequency E.g., input signal captured as

the sum of 4 cosine functions

Once in frequency domain, certain manipulations become trivial (e.g., filtering)



actuatorsactuators


Digital-to-Analog (D/A) Converters

Various types, can be quite simple, e.g.:


3

0

3

0123

2

842

i

ii

ref

refrefrefref

xR

VR

Vx

R

Vx

R

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refi

iref xnatR

RVx

R

RVV

Due to Kirchhoff‘s laws:

Due to Kirchhoff‘s laws:

Current into Op-Amp=0:

Hence:

Finally:

Output voltage no. represented by x


Reconstruct Analog from Digital?

According to Nyquist theorem:

Analog input to sample-and-hold can be precisely reconstructed from its output if

sampling frequency double the highest input frequency in input voltage and assuming voltages remain analog.

Digitizing values in the A/D generates additional uncertainty preventing precise reconstruction of initial values. Can be modeled as additional noise.

S/H A/D-converter D/A-converter

= ?

Inter-polate

Will this work?


Control Systems

actuatorsactuators


Control Systems

Control systems are a common class of embedded systems

Goal is to make a system’s output track a desired reference valueCruise control, thermostat, VCR tape speed, etc.

We’ll take a look at open-loop and closed-loop control systems


Control System

Control physical system’s output By setting physical system’s input

Tracking

E.g. Cruise control Thermostat control Disk drive control Aircraft altitude control

Difficulty due to Disturbance: wind, road, tire, brake; opening/closing door… Human interface: feel good, feel right…


Tracking

Good tracking Bad tracking


Open-Loop Control Systems

Plant Physical system to be controlled

Car, plane, disk, heater,…

Actuator Device to control the plant

Throttle, wing flap, disk motor,…

Controller Designed product to control the plant


Open-Loop Control Systems Output

The aspect of the physical system we are interested in Speed, disk location, temperature

Reference The value we want to see at output

Desired speed, desired location, desired temperature

Disturbance Uncontrollable input to the plant imposed by environment

Wind, bumping the disk drive, door opening


Other Characteristics of open loop

Feed-forward controlDelay in actual change of the outputController doesn’t know how well thing goesSimpleBest use for predictable systems


Closed Loop Control Systems

SensorMeasure the plant output

Error detectorDetect Error

Feedback control systemsMinimize tracking error


Benefit of Computer Control

Cost!!! Expensive to make analog control immune to

Age, temperature, manufacturing error

Computer control replaces complex analog hardware with complex code

Programmability!!! Computer Control can be “upgraded”

Change in control mode, gain, are easy to do

Computer Control can be adaptive to change in plant Due to age, temperature, …etc

“future-proof” Easily adapt to change in standards,..etc


Summary


ConvertersA/D and D/A

Signal Processing

Control Systems

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