PCB Components
Lecture 2
Engineering World Health
Ohm’s Law
Voltage = Current × Resistance
• Units of voltage are volts (V), where 1 V = 1 J/C.
• Units of current are amperes (A), where 1 A = 1 C/s.
• Units of resistance are ohms (Ω).
https://learn.sparkfun.com/tutorials/transistors/extending-the-water-analogy
Voltage Source
• Has two terminals
– Positive terminal has higher
potential than negative terminal.
• Voltage (and thus current)
reverses periodically in
alternating current (AC)
circuits.
• Direct current (DC) produces a
fixed voltage, so current flows
in one direction.
• Batteries are voltage sources.
https://learn.sparkfun.com/tutorials/how-to-read-a-schematic
Flow Notations
• Circuit symbols use conventional flow notation.
http://www.rare-earth-magnets.com/t-conventional-vs-electron-flow.aspx
Resistor
• Limits the amount of current that flows in
a circuit
• Has no polarity (can be mounted in either
direction).
• Two types of resistors:
– Fixed (two terminals)
– Variable
• Potentiometers (three terminals)
• Rheostats (two terminals)
https://learn.sparkfun.com/tutorials/resistors
https://learn.sparkfun.com/tutorials/how-to-read-a-schematic
Resistor Color Codes
http://itll.colorado.edu/images/uploads/resistorchart.jpg
Capacitor
• Stores electric charge
– Discharges it quickly, unlike a
battery
• Two types of capacitors:
– Non-polarized (ceramic)
– Polarized (electrolytic)
• Has two terminals
– If polarized, long leg is positive
and short leg is negative.
• Capacitance is measured in
units of farads (F).
http://www.diystompboxes.com/pedals/Caps.jpg
https://learn.sparkfun.com/tutorials/how-to-read-a-schematic
http://www.instructables.com/id/Arduino-WaveformGenerator-Shield/step4/220uF-Capacitors/
Capacitor Codes
http://h3laboratories.com/w/index.php?title=Capacitor_codes
Capacitor Construction
• Two conducting plates separated by a dielectric
(insulator)
• Charges until the capacitor’s voltage equals the supply
voltage
• Discharges when you remove the power source and
reconnect it to a closed circuit
https://learn.sparkfun.com/tutorials/capacitors
Charging and Discharging
https://learn.sparkfun.com/tutorials/capacitors
Switch
• Closed circuit when on and
open circuit when off.
• Must have at least two
terminals
• Switch types include push
button, rocker, etc.
• Orientation does not matter.
https://learn.sparkfun.com/tutorials/switch-basics
Switch Pole and Throw
• Pole: number of separate circuits a single switch can
control
• Throw: number of possible outputs per pole
https://learn.sparkfun.com/tutorials/switch-basics
Diode
• Forces current to move in
one direction
• Has two terminals
• Polarized (must be installed
in the correct direction)
– Anode (positive terminal)
– Cathode (negative terminal)
• Marked with a stripe
https://learn.sparkfun.com/tutorials/diodes
http://www.robotroom.com/RoundaboutPCBs/Diode.jpg
Diode Construction
• Diodes are the simplest of semiconductor devices.
– Consists of a positive p-side (hole-rich) and a negative n-side
(electron-rich)
• Holes diffuse to n-side and electrons diffuse to p-side,
forming a depletion region at equilibrium.
– Depletion region’s electric field opposes this diffusion of carriers.
http://www.schoolphysics.co.uk/age16-19/Electronics/Semiconductors/text/Semiconductor_diode/index.html
Forward and Reverse Bias
• Forward bias decreases the width of the depletion layer,
allowing current to flow.
• Reverse bias increases the width of the depletion layer,
preventing current flow.
http://www.schoolphysics.co.uk/age16-19/Electronics/Semiconductors/text/Semiconductor_diode/index.html
Light-Emitting Diode (LED)
• They are everywhere!
• Polarized
• Two terminals
– Negative cathode: short leg
and flat edge
– Positive anode: long leg
and curved edge
http://www.e-dan.co.uk/pc/led.GIF
http://www.robotroom.com/RoundaboutPCBs/LED.jpg
https://learn.sparkfun.com/tutorials/light-emitting-diodes-leds
Pretty Lights
https://i.imgur.com/lbiiY9e.gif
https://i.imgur.com/FGISM.gif
https://i.imgur.com/dBT42iP.gif
http://i.minus.com/iWeQmL7k5W35j.gif
Bipolar Junction Transistor (BJT)
• Has three terminals
• PNP- and NPN-type
• Acts as a switch and amplifier
– Modes include saturation (on), cutoff (off), and active (amplify).
• Consists of a collector, base, and emitter
– Small base current (between base and emitter) controls the main
collector current (between collector and emitter).
http://www.allaboutcircuits.com/vol_3/chpt_4/1.html
http://www.mikroe.com/old/books/keu/04.htm
Simple Transistor Circuit
http://www.technologystudent.com/elec1/transis1.htm
Integrated Circuit (IC)
• Microchip containing up to
billions of resistors,
transistors, capacitors, etc.
• Can perform many functions
(e.g., timer, oscillator, and
memory)
• Polarized (look for the notch)
• Heat-sensitive!
– Solder the IC socket first, then
insert the IC into the socket.
https://learn.sparkfun.com/tutorials/integrated-circuits
555 Timer IC Example
http://home.cogeco.ca/~rpaisley4/LM555.html