PROJECT: Cookie Timer
Step 1 - Build the Project

The cookie timer combines an indicator light with a software timer and a light and speaker alarm and some math to ensure the timer is working in 10 second increments. 

Step 2 - Upload the Code

/* * Use a button on 4 to add 5 second increments to a timer. Press the 'Go' button * on 12 to start the timer. To stop the timer alarm, press both buttons at once. */ byte pressCount = 0; //Each button press increases timer by secondsPerPress const byte speaker = A5; const byte led = A0; void setup() { pinMode(12, INPUT_PULLUP); //Go! button pinMode(4, INPUT_PULLUP); //add time button pinMode(led, OUTPUT); pinMode(speaker, OUTPUT); } void loop() { //Setting up the timer by pressing A5 to add 10 seconds to the timer if (digitalRead(4) == LOW) { digitalWrite(led, HIGH); pressCount++; delay(250); //Holding button for more than 1/4 second will count twice digitalWrite(led, LOW); } //if 'start' button pressed, flash how many 10 second increments and //start the countdown with one blink per second of countdown if (digitalRead(12) == LOW) { for (int i = 0; i < pressCount; i++) { digitalWrite(led, HIGH); tone(speaker, 650); delay(250); noTone(speaker); digitalWrite(led, LOW); delay(250); } const int secondsPerPress = 10; //10 second increase in timer per press unsigned long timer = (secondsPerPress * pressCount); //Count down the timer one second at a time until it hits 0 while (timer > 0) { digitalWrite(led, HIGH); delay(500); digitalWrite(led, LOW); delay(500); timer--; } //When time is up, play alarm until both buttons pressed while (digitalRead(4) && digitalRead(12) != LOW) { tone(speaker, 650); delay(100); noTone(speaker); delay(100); tone(speaker, 950); delay(100); noTone(speaker); delay(100); } pressCount = 0; //Reset button presses for next timer delay(500); } } // Try to convert this entire program to use only millis. The alarm check // will work like: if millis-timerVariable > alarmTime, ring alarm. // (c) 2017 Let's Start Coding. License: www.letsstartcoding.com/bsdlicense
 

Step 3 - Read the Walkthrough

The pressCount variable holds the number of times you have increased the timer by a 10 second increment. After setting up the ‘add time’ button and the ‘go!’ button as INPUT_PULLUPs and the LED and speaker as OUTPUTs, the rest of the code is a series of steps that can be broken down into small pieces.

The first ‘if’ statement in the loop looks for the ‘add time’ button to be pressed. If it’s pressed, the indicator light will illuminate and the pressCount is increased by one, then the indicator light turns off.

The second ‘if’ statement watches for the ‘go’ button. When it is pressed, the code drops into a ‘for’ loop that blinks the pressCounts and beeps a tone so you’re sure how many 10 second increments you added to the timer.

You then create the variables that define the number of seconds you want to add to your time each time you press the ‘add time’ button. The timer variable then multiplies that ‘time added per press’ by the pressCount to get a total number of seconds on your timer.

Next is a ‘while’ loop, which is useful when you’re not sure how many times a loop will need to repeat. With a ‘for’ loop, the loop will run a set number of times. With a ‘while’ loop the loop will run until the condition after ‘while’ is untrue. For this ‘while’ loop, you’re saying “write the light HIGH, wait half a second, write the light LOW, wait half a second, take 1 off of the timer number, and repeat”. This effectively reduces timer by 1 every second and gives a blink so you know the timer is running.

When the code falls through this first ‘while’ loop, it falls into another ‘while’ loop. The conditions of this ‘while’ loop are “as long as the button on 4 and the button on 12 are not both pressed, do the things in this ‘while’ loop”. This check means that you have to press both of the buttons at the same time to stop the alarm.

Unless that condition is false (meaning both buttons are pressed) the alarm will continue alternating between a tone of 650 and 950 and flashing the light on. Once the conditions are false, the code drops through this second ‘while’ loop, resets the pressCount, and is ready to start again!