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 Resisto r 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 X White X Grey X Purple X Blue X Green 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

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-meter Oscilloscope

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