ECE 101 An Introduction to Information

Technology

Digital Sensors

Unit Prefixes

tera T 1012

giga G 109

mega M 106

kilo k 103

deci d 10-1

centi c 10-2

milli m 10-3

micro 10-6

nano n 10-9

pico p 10-12

Information Path

InformationDisplay

Information Processor

& Transmitter

InformationReceiver and

Processor

Source ofInformation

DigitalSensor

TransmissionMedium

Electric Circuit Concepts• Charge, Q or q • Current, I or i – motion of charge (“through”)

– Direct current

– Alternating current

• Voltage or electric potential, V or v (“across”)– Motion of charge occurs due to a force pushing on it

– Work per unit charge is voltage

– If current through an element results in an expenditure of energy, than a voltage or potential drop occurs

– Battery

• Power, P = V*I, or p=v*i

Electric Circuit Laws• Multiple loads

– Series – same current– Parallel – same voltage

• Resistance and Ohm’s law, vR=iRR

• Kirchhoff’s Laws– Voltage law: v1 + v2 + v3 + …. = 0 (sum of

voltages around a loop is zero)

– Current law: i1 + i2 + i3 + …. = 0 (sum of currents at a node is zero)

Mechanical Switches

• Break the flow of electrical current

• May be activated by the outside environment, such as, change in switch position, temperature, acceleration

• May be activated in series– open: no alarm– closed: alarm activated

• May be activated in parallel– open: alarm activated– closed: no alarm

Mechanical Switches• Note the matrix arrangement for the

keyboard and the clever scheme to minimize the number of wires– Each key is a switch– Reduce the number of wires by using a matrix

of switches formed by rows and columns of keys

– Number of wires = number of columns + number of rows: NW = NC+ NR

– Number of switches, NS = NC* NR

Sensors or Transducers• Front end of information (electrical)

systems

• Converts physical energy into an electrical signal

• Produce the data to be transmitted, processed and/or stored

• Analog (continuous) or digital (example, a binary switch)

• Mechanical, optical, thermal, electrical

Optical sensors

• Visible [UPC (universal product code) using lasers)], IR (remote controls)

• Beam interrupt – presence of light may actuate a switch (often mechanical)

• Digital Data transmission – use of threshold– Noise and weather (attenuation) not as

significant– Beam intensity not a factor (good for cellular

telephone)

Optical Proximity Sensors

• Unlike beam interrupt, the the transmitter and receiver in the same device.

• Reading of Bar Codes, facsimile machines

• Note the clever way of reading the UPC code at an angle and the operation of an auto-focus camera. Trigonometry is key here!

Infrared (IR)

Range Sensors

Infrared (IR) Range Sensors

• Uses variation of proximity sensor to determine the range of an object for setting the focus of an auto focus camera

S

R

fxreceiver

transmitter

R/S = f/x

S and f fixed by camera design

Digital IR Range Sensors

Digital IR Range Sensors

• Uses an array of small detector elements - no determinations or calculations needed

S

R

f

receiver

transmitter

R/S = f/x

S and f fixed by camera design

Inverse Square Law

• Key law in physics, gravity, light intensity, Coulomb’s law in E&M…

• I=P/A where A=r2, or I~1/ r2

– Determines the spacing of antennas in cellular telephone system

– Can be used to locate a transmitting signal

Inverse Square Law

r = ro

R = Ro

I (r = ro) = P/(2r2) = I (r = ro) /2

r = ro

R = Ro