ECS642U Embedded Systems

Simple Electronics

William Marsh

Outline

• Aims• Resisters and ohms law• LED• Oscilloscope

Aim

• Basic ideas of electronics

• Ignorance– “Software is simple and easy to change” – “Electronics just bolts together. The world is

really digital”

• Know enough to know what you don’t know– … and then ask

Voltage, Current and Resisters

Voltage and Current

• Current– Movement of electric charge (Amps)– Water analogy: volume of water flowing

• Volt– Relates to force on an electric charge (Volts)– Water analogy: pressure of water

• Water: pressure leads to flow• Electricity: voltage leads to current

Resistors

• A resistors resists the flow of current– Larger resistor less current

• Electrons do not flow frely– Collisons electrical

resistance– … and heat

Resistor Symbol

Carbon Film Through

Hole Resistor

Surface Mount

Resistors

Resistor Examples

Resistor

Contact leads

Symbol for resistor

Resistor Labels

• Resistance and power ratings.• Colour bars resistance• Right most colour tolerance• Three digits: A, B, C

Resistor Color Codes

x.01-Silver

X10000000009White

X1000000008Grey

X100000007Purple

X10000006Blue

X1000005Green

X100004Yellow

X10003Orange

X1002Red

X101Brown

X10Black

x.1-Gold

MultiplierDigitBand color

5%Gold

10%Silver

2%Red

1%Brown

ToleranceColor

None ±20%

Example

• The first band is yellow 4• The second band is violet 7• The third band is red, so the multiplier is • Resistor value is )%(51047 2

210

Ohms

• Resistance is measured in Ohms– 1 ohm is the resistance that requires 1 volt

to causes 1 amp of current to flow

Ohm's Law

• Resistance R• Voltage V• Current I

• V = I * R– Voltage need to get

current I through resistor R

• I = V / R– Current resulting

from V applied to R

• R = V / I – Resistance seen

when V causes current I

Ohm's Law – Application I

• Must not draw too much current from KL25Z

• V is 3volts

• Current limit 25mA

• Example– R = 100 Ohms– I = 3 / 100 = 30 mA– NOT OK

• Example– R = 300 Ohms– I = 10 mA– OK

Devices and Circuits

Switch

• Why R?

• When switch open see supply voltage

• R must be large• Pull-up

Printed Circuit Board

• Connect components

• Where are the wires?

Breadboard

• Prototyping

LED and current

What are LEDs?

• Light Emitting Diodes• Diode Symbol + Arrows for light• Points to ground

Measuring

Multi-meterOscilloscope

Digital Multimeter

• Voltmeter– Parallel connection

• Ammeter– Series connection

• Ohmmeter– Without any power supplied

• Adjust range (start from highest limit if you don’t know)

Summary

• It's all fun

• Voltage like pressure• Current like flow rate

• Ohms law: V = I * R