Basic of Analog and Digital sensors.ppt

This documents is useful for an embedded engineer who is advancing in Internet of things.

1. By
SanthiKumaran
ACEIoT

2. Types of Signals
Analog:
An analog signal is a continuous signal and is often represented
by a V(t).
A dimmerlight switch continuously increases/decreases the
current.
Digital:
A digital signal is a discrete time signal, binary signal.
An On/Off light switch applies a fixed, predetermined voltage.

3. Analog and Digital Signals
Light intensity
Temperature
Pressure

4. Analog-to-Digital Conversion
Sampling–converts the continuous signal into a series of discrete
analog signals at periodic intervals
Quantization–each discrete analog is converted into one of a finite
number of (previously defined) discrete amplitude levels
Encoding–discrete amplitude levels are converted into digital code
Variable
Time
Analogue Signal
1001 1101 0101
Discrete
Variables

5. Features of an ADC
Sampling rate –rate at which continuous analog signal
is polled e.g. 1000 samples/sec
Quantization –divide analog signal into discrete levels
Resolution –depends on number of quantization levels
Conversion time –how long it takes to convert the
sampled signal to digital code
Conversion method –means by which analog signal is
encoded into digital equivalent
Example –Successive approximation method

6. Sensors and Actuators
Sensor(e.g., thermometer)
a device that detects/measures a signal or stimulus
acquires information from the “real world”
Actuator(e.g., heater)
a device that generates a signal or stimulus
real
world
sensor
actuator
intelligent
feedback
system
sensor
input
signal
(measurand)
microcontroller
signal processing
communication
sensor data
analog/digital
network
display
Typical Electronic Sensor System

7. Analog Sensors
Sensorsthatproducecontinuousanalogoutputsignalandthese
sensorsareconsideredasanalogsensors.
Thiscontinuousoutputsignalproducedbytheanalogsensorsis
proportionaltothemeasurand.
Practicalexamplesofvarioustypesofanalogsensorsareas
follows:accelerometers,pressuresensors,lightsensors,sound
sensors,temperaturesensors,andsoon.

8. Accelerometers
Analogsensorsthatdetectchangesinposition,velocity,orientation,
shock,vibration,andtiltbysensingmotionarecalledas
accelerometers.
Theseaccelerometersareavailableasanaloganddigitalsensors,based
ontheoutputsignal.Analogaccelerometerproducesaconstantvariable
voltagebasedontheamountofaccelerationappliedtotheaccelerometer.

9. Light sensor
Analogsensorsthatareusedfordetectingtheamountoflightstriking
thesensorsarecalledaslightsensors.Theseanaloglightsensorsare
againclassifiedintovarioustypessuchasphoto-resistor,Cadmium
Sulfide(CdS),and,photocell.

10. Sound Sensor
Analogsensorsthatareusedtosensesoundlevelarecalledassound
sensors.Theseanalogsoundsensorstranslatetheamplitudeofthe
acousticvolumeofthesoundintoanelectricalvoltageforsensingsound
level.Thisprocessrequiressomecircuitry,andutilizesmicrocontroller
alongwithamicrophoneforcreatingananalogoutputsignal.

11. Pressure Sensor
Theanalogsensorsthatareusedtomeasuretheamountofpressure
appliedtoasensorarecalledasanalogpressuresensors.Pressure
sensorwillproduceananalogoutputsignalthatisproportionaltothe
amountofappliedpressure.Thesepiezoelectricsensorsareusedforthe
generationofelectriccharge.

12. Analog Temperature sensor
Temperaturesensorsarewidelyavailableasbothdigitalandanalog
sensors.Typicallyusedanalogtemperaturesensorsarethermistors.
Thermistorisathermallysensitiveresistorthatisusedfordetecting
changesintemperature.Ifthetemperatureincreases,thentheelectrical
resistanceofthermistorincreases.Similarly,iftemperaturedecreases,
thentheresistancedecreases.

13. Ultrasonic sensors
Thehighfrequencysoundwavesgeneratedbyactiveultrasonic
sensorsarereceivedbackbytheultrasonicsensorforevaluatingthe
echo.Thus,thetimeintervaltakenfortransmittingandreceivingthe
echoisusedfordeterminingthedistancetoanobject.But,passive
ultrasonicsensorsarejustusedfordetectingultrasonicnoisewhichis
presentunderspecificconditions.

14. Digital Sensors
Electronicsensorsorelectrochemicalsensorsinwhichdataconversion
anddatatransmissiontakesplacedigitallyarecalledasdigitalsensors.
Thesedigitalsensorsarereplacinganalogsensorsastheyarecapable
ofovercomingthedrawbacksofanalogsensors.Indigitalsensors,the
signalmeasuredisdirectlyconvertedintodigitalsignaloutputinsidethe
digitalsensoritself.

15. Digital Sensors
Button
Motion
Bumper Switch Sensor
Lever
Limit Switch Sensor
Ultrasonic sensor

16. Digital Temperature Sensor
DS1620isadigitaltemperaturesensorthatprovidestemperatureofdevice
with9-bittemperaturereadings.Itactsathermostatwithitsthreethermal
alarmoutputs.Ifthetemperatureofdeviceisgreaterthanorequaltouser
definedtemperatureTH,thenTHIGHisdrivenhigh.Ifthetemperatureof
thedeviceislessthanorequaltouserdefinedtemperatureTL,thenthe
TLOWisdrivenhigh.IfthetemperatureofthedeviceexceedsTHand
remainshighuntilitfallsbelowthatofTL,thentheTCOMisdrivenhigh.

17. Digital Accelerometers
Themethodofgenerationofvariablefrequencysquarewaveoutputby
thedigitalaccelerometeriscalledaspulse-widthmodulation.Theoutput
PWMsignal,pulsewidthordutycycleisproportionaltotheacceleration
value.

18. Sensors for a
Robot
Touch sensorstell the robot
when it bumps into
something.
Light sensorsmeasure light
intensity.
gyroscopestell the robot which
direction is up.
Heat Sensorswhich measure
temperature.
Ultra Sonic Rangerstell the robot
how far away objects are.
1. Resistive
2. Infra-red
3. Light
4. Sonar
5. Other

19. Other Sensors
RFID
Barcode
Proximity
Vision
Gyroscope
Compass
Tilt/Acceleration
Etc.

21. Actuators
Hardwaredevicesthatconvertacontrollercommand
signalintoachangeinaphysicalparameter
Thechangeisusuallymechanical(e.g.,positionor
velocity)
Anactuatorisalsoatransducerbecauseitchanges
onetypeofphysicalquantityintosomealternative
form
Anactuatorisusuallyactivatedbyalow-level
commandsignal,soanamplifiermayberequiredto
providesufficientpowertodrivetheactuator

22. THANKYOU