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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
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 2
Simplified Block Diagram
actuatorsactuators
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 3
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)
May require analog interface
solenoid mic
laser diode/transistor
speaker
dc motor
compass
accelerometer
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 4
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.
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 5
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
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 6
Charge-coupled devices (CCD)
Image Sensors: Based on charge transfer to next pixel cellImage Sensors: Based on charge transfer to next pixel cell
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 7
CMOS Image Sensors
Based on standard production process for CMOS chips, allows integration with other components.
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 8
Comparison CCD/CMOS sensors
Sou
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B. D
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age
sens
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P
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)
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 9
Example: Biometric Sensors
Example: Fingerprint sensor (© Siemens, VDE):Example: Fingerprint sensor (© Siemens, VDE):
Integrated into ID mouse.
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 10
Example: Artificial eyes
© Dobelle Institute(www.dobelle.com)
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 11
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)
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 12
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”)
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 13
Simplified Block Diagram
actuatorsactuators
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 14
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)
May require analog interface
solenoid mic
laser diode/transistor
speaker
dc motor
compass
accelerometer
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 15
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…..
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 16
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
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 17
MEMS Actuators
Huge variety of actuators and output devices.
Microsystems motors as examples (© MCNC)(Dimensions in the order of several microns)
(© MCNC)
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 18
Actuators
Courtesy and ©:E. Obermeier, MAT,
TU Berlin
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 19
Simplified Block Diagram
actuatorsactuators
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 20
Sample-and-Hold Circuit
Sampling: how often the signal is converted.Quantization: how many bits used for sampling.
Model: Vx = Ve when Clock = 1
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 21
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
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 22
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
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 23
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
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 24
Flash A/D Converter
Parallel comparison with reference voltage Speed: O(1) HW complexity: O(n)
n= # of distinguished voltage levels
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 25
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.
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 26
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
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 27
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
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 28
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)
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 29
Simplified Block Diagram
actuatorsactuators
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 30
Digital-to-Analog (D/A) Converters
Various types, can be quite simple, e.g.:
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 31
3
0
3
0123
2
842
i
ii
ref
refrefrefref
xR
VR
Vx
R
Vx
R
Vx
R
VxI
0'1 IRV
'II
01 IRV
3
0
131 )(8
2i
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
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 32
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?
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 33
Control Systems
actuatorsactuators
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 34
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
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 35
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…
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 36
Tracking
Good tracking Bad tracking
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 37
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
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 38
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
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 39
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
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 40
Closed Loop Control Systems
SensorMeasure the plant output
Error detectorDetect Error
Feedback control systemsMinimize tracking error
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 41
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
ICS212 WQ05 (Dutt) Hardware Components: Sensors, Actuators, Converters 42
Summary
Sensors and Actuators
ConvertersA/D and D/A
Signal Processing
Control Systems