Fading led with push button

Question

I need to make for school a project. That when i hold a button it fades. But when you let go the button it needs to stop immediately. But when i you hold the button again it needs to start again with fading but the brightness needs to start from 0. I have a program but when i press again it just starts from the previous brightness. Pls help. This is my code:

int led = 9; 
int brightness = 5; 
int fadeAmount = 5; 
void setup() {
 Serial.begin(9600);
 pinMode(led, OUTPUT);
}
void loop() {
 int val = digitalRead(2);
 Serial.println(val);
if (val==HIGH){
 analogWrite(led, brightness);
 brightness = brightness + fadeAmount;
 if (brightness <= 0 || brightness >= 255) {
 fadeAmount = -fadeAmount; }
 delay(100);
}
else{ 
 digitalWrite(9, LOW);
}
}

Answer 1

The main problem is you have to reset brightness to 0 when the switch is LOW. Btw, I did not test the sketch, only compiled it.

int led = 9; 
int brightness = 5; 
int fadeAmount = 5; 
void setup() {
 Serial.begin(9600);
 pinMode(led, OUTPUT);
}
void loop() {
 int val = digitalRead(2);
 Serial.println(val);
if (val==HIGH){
 analogWrite(led, brightness);
 brightness = brightness + fadeAmount;
 if (brightness <= 0 || brightness >= 255) {
 fadeAmount = -fadeAmount; }
 delay(100);
}
else{ 
 digitalWrite(9, LOW);
 brightness = 0; // Restart with brightness 0
}
}

Some other improvements result in:

#define LED_PIN 9 
#define DELAY_TIME 100 
int brightness = 5; 
int fadeAmount = 5; 
void setup() {
 Serial.begin(9600);
 pinMode(LED_PIN, OUTPUT);
}
void loop() {
 int switchButton = digitalRead(2);
 Serial.println(switchButton);
 if (switchButton == HIGH) {
 analogWrite(LED_PIN, brightness);
 brightness += fadeAmount;
 if ((brightness <= 0) || (brightness >= 255)) {
 fadeAmount = -fadeAmount; 
 }
 delay(DELAY_TIME );
 }
 else { 
 digitalWrite(LED_PIN, LOW);
 brightness = 0; // Restart with brightness 0
 }
}

Explanation

1. Always indent your code (so that { and } are clear, notice each new { increases the indentation by two spaces, each } decreases the indentation by two spaces.
2. For values that do not change use a #define. This prevents (in this case) a few bytes not be stored in valuable memory space. Especially if you would use arrays this is important.
3. You used 9 in digitalWrite(9, LOW); which was probably a mistake, always use defines wherever possible. I also would use #define DELAY_TIME 100 instead of the hardcoded 100 value.
4. I addes some spaces before/after values (like switchButton == HIGH). It doesn't matter if you do or not, but be consequent.
5. Use good variable names (switchButton is more clear than val.
6. Use brightness += fadeAmount; instead of brightness = brightness + fadeAmount;; this is the normal way of increasing (or decreasing/multiplying/whatever) the value of a variable.
7. Use ( and ) in non trivial if statements like if ((brightness <= 0) || (brightness >= 255)), this could save you hours of searching in case you ever make a mistake (in this case there is no functional change).

Good luck with your project.

• Duncan C: Wow, a bounty of good coding advice! (Voted)