Arduino Intro Labs for Tangible Computing - 4. Lab 2

Arduino Intro Labs for Tangible Computing

4. Lab 2 - Tug of War

4.1 Introduction

The previous lab exercise was a very intense introduction to some key ideas in hardware circuits and Arduino C/C++ programs. This lab does not introduce any new concepts, but instead asks you to take an existing sketch (hardware plus software) and "enhance" it. The outcomes of this part are:

Handle simultaneous inputs from multiple sources (two buttons).
Use chains of if-then conditionals.
Use variables to introduce additional state and behaviour (for example detecting that a button has gone down, then back up, and acting only after it has gone back up.)
Begin developing diagnostic/debugging skills.

The circuit below, and accompanying program, implement a tug of war game. Please go ahead and construct it as shown below, and start a new Arduino sketch with the Tug of War code given below. If you're having troubles you can try pulling out all the wires and try again. Sometimes it's faster just to re-wire everything rather than trying to find out which piece of hardware is an issue.


Arduino Mega	Arduino Uno
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code/Lab_TugOfWar/Lab_TugOfWar.ino

/* Tug of war game:

Two players, Player 1 and Player 2, are at a

board consisting of 2 push buttons and 3 LEDS

There are 3 LEDs

RED1 GRN RED2

and 2 buttons

B1 B2

The objective is to push your button faster than your opponent

so that when time runs out you have the rope on your side.

Whoever has pushed their button the most times will be

winning, and their red LED will turn on. If the two buttons

are within Threshold of each other, then the players are

currently tied, and the green LED will be on.

*/

int P1LEDLowPin = 10;

int P2LEDLowPin = 8;

int LEDEvenPin = 9;

int P1ButtonPin = 7;

int P2ButtonPin = 6;

void setup() {

// configure LED pins to be a digital outputs

pinMode(P1LEDLowPin, OUTPUT);

pinMode(P2LEDLowPin, OUTPUT);

pinMode(LEDEvenPin, OUTPUT);

// set button pins to INPUT and

// turn on internal pull up resistor

pinMode(P1ButtonPin, INPUT);

digitalWrite(P1ButtonPin, HIGH);

pinMode(P2ButtonPin, INPUT);

digitalWrite(P2ButtonPin, HIGH);

}

/* PushCount is incremented when player 1 pushes their

button, and decremented when player 2 pushes their

button. So if it is > 0 player 1 has made more pushes

and if it is < 0 player 2 has made more pushes.

*/

int PushCount = 0;

/* PushCount has to be Threshold far away from zero before a

player is considered to be winning.

*/

int Threshold = 5;

void loop() {

if ( digitalRead(P1ButtonPin) == LOW ) {

PushCount++;

}

if ( digitalRead(P2ButtonPin) == LOW ) {

PushCount--;

}

if ( PushCount > Threshold ) {

digitalWrite(P1LEDLowPin, HIGH);

digitalWrite(P2LEDLowPin, LOW);

digitalWrite(LEDEvenPin, LOW);

} else if ( PushCount < (0-Threshold) ) {

digitalWrite(P1LEDLowPin, LOW);

digitalWrite(P2LEDLowPin, HIGH);

digitalWrite(LEDEvenPin, LOW);

} else {

digitalWrite(P1LEDLowPin, LOW);

digitalWrite(P2LEDLowPin, LOW);

digitalWrite(LEDEvenPin, HIGH);

}

// wait 50 mS for any button bounce to die out

delay(50);

}

Your tasks:

With just one red LED, it is hard to see how well you are doing. Add two more LEDs to indicate when the rope is even more on your side. That is, instead of having the leds

RED GREEN RED we have RED RED GREEN RED RED

You need to add a second higher threshold, called HighThreshold. This way, when a player has more than the Threshold, the red LED nearest the green is on, and when they have more than the HighThreshold, both of their LEDs are on.
Recall what we said about conditionals in this section.

Questions:

What happens if you hold your button down instead of pushing and releasing thit? How would you fix this problem so that you have to release the button before pushing it again?
How would you add a timer to the game so that when the timer ran out, the game would stop accepting button presses, and turn on an additional LED to indicate that the game is over? One way would be to introduce a counter variable that would decrease at the end of each loop of the program. Then when the counter reaches zero, the game ends.
The PushCount variable is an int, so that means that it has a maximum range of -32768 to 32767. What would happen if one player ever got more than this far ahead of the other player?

4. Lab 2 - Tug of War
Arduino Intro Labs for Tangible Computing / Version 1.00 2012-09-24