Student Lecture Session 3AnalogWrite, PWM, Fading LED's,

Multiple LED's via PWM, Tri-Color LEDsCases, Switch Case, goto

Thai Le, Bruce Drummond, Stephen Varga

Pulse Width ModulationPulse Width Modulation

on off 50% or fade?

0v 5v2.5v

analog

digital

0v / 5v

= 50% brightness

= 0% or 100%

Analog Write

0volts

5volts

pulse widthdealy

delay

0volts

5volts

delay

Fading modulation - analogWrite(ledpin1, pulsewidth); // 255 brightest to ~ 0

“equivalent voltage”

Fading LED’sint value = 0; // variable to keep the actual value int ledpin = 9; // light connected to digital pin 9

void setup() { // nothing for setup } void loop() {

for(value = 0 ; value <= 255; value+=5) // fade in (from min to max) { analogWrite(ledpin, value); // sets the value (range from 0 to 255) delay(30); // waits for 30 milli seconds to see the dimming effect }

for(value = 255; value >=0; value-=5) // fade out (from max to min) { analogWrite(ledpin, value); delay(30); } }

Multiple LED’s via PWM

Tri-Color LED’s

• Two types

• Common Anode

• Connect common pin to ground

• Common Cathode

• Connect common pin to +5V

Tri-Color LED’s

Tri-Color LED’s

Switch/Case Statement

• Used when in place of complicated if/else logic statements

• Functionality is the same, but easier to read,modify and use.

• Preferred by advanced programmers, however easy to use for everyone

Basic Syntax

• Statements start with “Switch(variable or statement)” syntax

• ie: Switch(skyIsBlue) or Switch(myVariable)

• Variable or statement is evaluated by the “Switch()” statement, and the results are then accessed by a “Case” statement

Basic Syntax

• “Case” statements are used to evaluate all possible values of the “Switch()” results

• Switch(skyIsBlue) { Case 0: //Sky Isn’t Blue, do something Case 1://Sky is Blue, do something else}

Syntax

• “Default” is a special case, used if none of the “Case” values are met

• Switch(skyIsBlue) { Case 0: //Sky Isn’t Blue, do something Case 1://Sky is Blue, do something else Default://Do the default functionality}

Syntax• Each condition must end in a “break;”

• If “break;” is not present, the statement will continue to execute. This may or may not be useful.

• Switch(skyIsBlue) { Case 0: //Sky Isn’t Blue, do something break; Case 1: //Sky is Blue, do something else break; Default: //Do the default functionality break;}

Bringing it all together• Here is an example of the full syntax of a Switch/Case Statement

• int whichLED=3;

Switch(whichLED) { Case 0: //Code to Light LED #0 Case 1: //Code to Light LED #1 Case 2: //Code to Light LED #2 Case 3: //Code to Light LED #3 Default: //Turn off all the LEDs}

Bringing it all together

int whichLED=3;

Switch(whichLED) { Case 0: //Code to Light LED #0 break; Case 1: //Code to Light LED #1 break; Case 2: //Code to Light LED #2 break; Case 3: //Code to Light LED #3 break; Default: //Turn off all the LEDs break;}

int whichLED=3;

if(whichLED==0) { //Code to Light LED #0} else if (whichLED==1) { //Code to Light LED #1} else if (whichLED==2) { //Code to Light LED #2} else if (whichLED==3) { //Code to Light LED #3} else { //Turn off all the LEDs}

if else Statement Switch• Here is a comparison of the same statment in if/else format

goto Statements

• Allow you to control the flow of your program

• Takes the program out of its ordinary logical execution pattern and allows you to label places in the program to jump to

• Pretty much universally unrecommended

goto Example

• Example from Arduino sitefor(byte r = 0; r < 255; r++){ for(byte g = 255; g > -1; g--){ for(byte b = 0; b < 255; b++){ if (analogRead(0) > 250){ goto bailout;} // more statements ... }

}}bailout: