Transcript Electron Flow

Electronics
Unit 1 – Fundamentals
Electricity – study of the flow of electrons.
Electronics – study of the control of electron flow.
Conductor -
Material w/ loosely held e-; e- flow
easily (metals)
Insulator -
Material w/ e- tightly bound to the
nucleus (nonmetals)
For e- to flow in a conductor there must be…
1. A difference in electric potential (voltage) b/w
points.
2. A complete path (circuit)
Voltage (V) -
Push of electrons (volts)
also known as electromotive force (emf)
Current (I) -
Flow of electrons (amps)
Resistance (R) Power (P) -
Restriction of electron flow (ohms, Ω)
Electrical energy per time (watt)
Ohm’s Law
V=IxR
Twinkle twinkle little star, voltage equals I times R
Power Law
P=IxV
Power equals current times voltage
Watts = amps x volts
Metric Prefixes
Mega – 1,000,000 = 106
Kilo – 1,000 = 103
-------------
Milli – 1/1,000 = 0.001 = 10-3
Micro – 1/1,000,000 = 0.000001 = 10-6
Nano – 1/1,000,000,000 = 0.000000001 = 10-9
Pico – 10-12
Examples
Calculate the current (in amps) in a 200 ohm
resistor in a 120 Volt circuit.
Express this answer in milliamps (mA).
Examples
Calculate the current in a 100 Watt light bulb on a
120 volt circuit.
Examples
Calculate the voltage across a 10 kilo-ohm resistor
that has 0.125 amps of current through it.
Types of Current
Direct Current (DC)
Electron flow in 1 direction (cells, batteries)
Conventional Current – flows from pos. to neg
(Thanks Ben F.)
Electron Flow – flows from neg. to pos.
Alternating Current (AC)
Electron flow constantly changes direction at certain
frequency (Hertz).
Schematic Symbols
DC Power (Battery)
Resistor
AC Power
Cells vs. Batteries
Cell Converts chemical energy to electrical energy.
AAA, AA, C, D all are rated 1.5 Volts
Battery Group of 2 or more cells connected together.
9 Volt battery consists of six 1.5 cells
Cell & Batteries
Capacity Amount of electricity that a battery will give off before fully
discharging; measured in Amp-hours.
Discharge Rate Rate at which current is drawn from battery.
The capacity of a battery depends on
its discharge rate.
Capacity @ lowest discharge rate (25 mA)
9-V
625 mAh
AAA
1250 mAh
AA
2850 mAh
C
8350 mAh
D
20500 mAh
In theory, a AAA can produce 1.25 A for 1 hour.
In reality, a AAA can’t produce 1.25 A.
Battery Capacities (Energizer)
9-Volt
AA
ASSIGNMENT:
Worksheet #1: Ohm’s Law
The Resistor Color Code
Memorize this code!!
47000 Ω or 47 kiloΩ
Resistors
• A resistor is typically used to control the
amount of current that is flowing in a
circuit.
• Resistance is measured in units of ohms
()
21
Resistors: Types and Package Styles
Carbon Film Resistors
Variable Resistors
(potentiometer)
4 Bands
Carbon Film Resistors
Surface Mount Resistors
5 Bands
22
Resistors: Size Comparison
23
Determining A Resistor’s Value
Color Code
Measured Value
• Resistors are labeled with
color bands that specify
the resistor’s nominal
value.
• The nominal value is the
resistor’s face value.
• A digital multi-meter can
be used to measure the
resistor’s actual
resistance value.
24
How To Read A Resistor’s Value
Resistor Color Code
25
Resistor Value: Example #1
Example:
Determine the nominal
value for the resistor
shown.
26
Resistor Value: Example #1
Example:
Determine the nominal
value for the resistor
shown.
Solution:
10 x 100  5%
1000  5%
1 K  5%
27
Resistor Value: Example #2
Example:
Determine the nominal
value for the resistor
shown.
28
Resistor Value: Example #2
Example:
Determine the nominal
value for the resistor
shown.
Solution:
39 x 100K  5%
3900000  5%
3.9 M  5%
29
Resistor Value: Example #3
Example:
? ? ?
?
Determine the color bands
for a 1.5 K  5% resistor.
30
Resistor Value: Example #3
Example:
? ? ?
?
Determine the color bands
for a 1.5 K  5% resistor.
Solution:
1.5 K  5%
1500  5%
15 x 100  5%
1:
Brown
5:
Green
100:
Red
5%:
Gold
31
Potentiometers – 3-terminal variable resistor
Rheostat – uses the center and 1 outer terminal
The resistance will be printed on it.
The center terminal is called the ‘wiper’ or center tap.
Inside a potentiometer
Potentiometer Schematic Symbol
Rheostat Schematic Symbol
Standard Resistor Values
10 12 15 18 22 27 33 39 47 56 68 82
100 120 150 180 220 270 330 390 470 560 680 820
1k
1.2k 1.5k 1.8k 2.2k 2.7k 3.3k 3.9k 4.7k 5.6k 6.8k 8.2k
10k 12k 15k 18k 22k 27k 33k 39k 47k 56k 68k 82k
100k 120k 150k 180k 220k 270k 330k 390k 470k 560k 680k 820k
1M
1.2M 1.5M 1.8M 2.2M 2.7M 3.3M 3.9M 4.7M 5.6M 6.8M 8.2M
Don’t assume all the resistors in the tray are what the tray claims.
Resistors are normally rated for ¼ or ½ watt.
For most circuits, a ¼ watt resistor will work.
Digital
Multimeter
(DMM)
Measuring Electrical Quantities
Voltage
Current
Measure across (parallel) device
Measure in series with device (break
open circuit
Resistance
Measure across the device (power off!)
Voltage Drop
Voltage across a device
Types of Circuits
Open
No electron flow (OFF)
Closed
Electrons are flowing (ON)
Series
1 path for electron flow. Each device
receives same I, Vdrop depends on R
Parallel
Short
More than 1 path for electon flow. Each
path receives the same voltage.
Electrons bypass the device.
Adding Resistors in Series
RT  R1  R2  ...
Adding Resistors in Parallel
1
1
1
 
 ...
RT R1 R2
The total resistance of a parallel circuit decreases as more
resistive paths are added.
Series Circuit Example
3V
R1 = 100
R2 = 220
1. Calculate the total resistance of the circuit.
2. Calculate the current flowing through R1 & R2.
3. Calculate the voltage across R1 & R2.
4. How much power is used by R1 & R2?
Parallel Circuit Example
3V
R1 = 100
R2 = 220
1. Calculate the total resistance of the circuit.
2. Calculate the current flowing through R1 & R2.
3. Calculate the voltage across R1 & R2.
4. How much power is used by R1 & R2?
Voltage Drop
Voltage across a device in a circuit.
Wire Types
Solid
Bare, Insulated or Enameled
Stranded
Insulated
Cable
2 or more insulated wires bound together.
Wire Sizes
American Wire Gauge (AWG)
Indicates wire diameter (thickness).
The smaller the wire, the larger the AWG number.
Thick wires can safely handle more current.
Wire Sizes
Switches
Switch –
device placed in a circuit to open and close
the circuit.
Toggle
Slide
Push
Button
Switches
Knife
Rotary
Rocker
Reed (Magnetic)
Tilt (mercury or ball)
Switches
Switches
SPDT – Single
Pole Double
Throw
Switches
Pole – set of 2 contacts that belong to a single
circuit.
Throw – one of two or more positions that a
switch can be in.
SPST – Single Pole Single Throw
Switches
SPDT – Single Pole Single Throw
aka “Three Way Switch”
Switches
DPDT – Double Pole Double Throw
Switches
SPST
SPDT
Normally Open – not ON until switch is pressed;
“press to make”
Normally Closed – ON until switch is pressed;
“press to break”
NO
NC
Momentary pushbutton switches
Tactile Switches
Upper pins connect to lower pins when pressed.
Soldering
Joining of metals by using a low-melting
point metal alloy (solder)
Soldering Iron
Soldering Gun
Solder
Solder is an alloy of TIN
(~60%) and LEAD (~40%)
Solder melts around 200° F
Rosin Core Solder (NOT ACID CORE!)
Useful Soldering Items
Soldering Iron Stand
Helping Hands
How to Solder
1. CLEAN SURFACES to be joined (steel wool or
sandpaper; lacquer thinner if necessary)
2. APPLY HEAT. Heat up connection using a
clean soldering-iron tip.
3. APPLY SOLDER. The solder should touch the
connection, not the iron tip. Solder will flow to
the hot spot.
4. REMOVE SOLDER.
5. REMOVE HEAT. Do not move connection
while it cools (solidifies).
How to Solder 2 Wires Together
How to Solder 2 Wires Together
How to Solder 2 Wires Together
Use the Helping Hands
How to Solder 2 Wires Together
Apply Heat
How to Solder 2 Wires Together
Apply Solder, Remove Solder, Remove Heat
A Good Soldered Connection
1. Does not have a ball or lump of solid solder.
2. Is shiny. Dull solder points indicate the wires
moved during cooling, making a weak
connection.
Heat Shrinking
Heat shrink tubing, when heated, will shrink to
about 50% of its original size.
Placed over an open connection between wires
and then shrunk (using heat gun) to insulate the
connection.
Desoldering
Removing the solder from a connection.
Desoldering Wick
(copper braid)
Desoldering Bulb
(copper braid)
ASSIGNMENT:
1. Solder solid leads onto a battery snap.
Red wire  Red wire
Black wire  Black wire
Apply red and black heat shrink tubing.
2. Solder two black wires to a speaker.
Show Tischer for credit.
Breadboard or Solderless Circuit Board
Positive bus
Negative bus
Breadboard or Solderless Circuit Board
Breadboard or Solderless Circuit Board
Breadboard - Used to build circuits temporarily.
- Do not run 9 volts across anything; always use
a resistor.
- Do not work on live circuits; have an ON/OFF
slide switch to check if circuit works.
- Use 22 AWG solid wire; do not insert wire in
breadboard more than ¼”
- Keep your circuits neat; don’t use wire that is
longer than necessary.
Breadboard - Used to build circuits temporarily.
- Keep your circuits neat;
don’t use wire that is longer than necessary.
minimize the amount of wire
build circuit to resemble the schematic layout
highlight schematic to show what you’ve done
Breadboard - Used to build circuits temporarily.
- Do not run 9 volts across anything; always use
a resistor.
- Do not work on live circuits; have an ON/OFF
switch to check if circuit works.
- Use 22 AWG solid wire; do not insert wire in
breadboard more than ¼”
- Keep your circuits neat; don’t use wire that is
longer than necessary.
What resistor should be used for a 9-V
battery to run an LED?
We need a resistor that will have a
voltage drop of (9 – 2.2 V) = 6.8 V
We also need a safe current of around
20 mA in the circuit.
R = V/I = 6.8 V/0.020 A
= 340 ohms
390 or 470 ohms would work.
1. Build this circuit
2. Add a potentiometer in series with the resistor
3. Substitute a photocell for the resistor.
Add a SPDT slide switch to the breadboard