Digital Input and Output with an Arduino

Momentary switch going into digital input with pull-down resistor, and two digital outputs controlling LEDs. If button pressed, yellow LED turns on. If button released, red LED turns on.

    void setup() {
    	pinMode(2, INPUT);
    	pinMode(3, OUTPUT);
    	pinMode(4, OUTPUT);
    }

    void loop() {
    	if (digitalRead(2) == HIGH) {
    		digitalWrite(3, HIGH);
    		digitalWrite(4, LOW);
    	}
    	else {
    		digitalWrite(3, LOW);
    		digitalWrite(4, HIGH);
    	}
    }

Combination Lock

Push a set of three buttons in the right order to “unlock” — LED turns on when successful. The correct combo, as seen in code as well as the image above, is btn1, btn3, btn2. There’s also a reset button to erase current combo input and start over.

byte btn1 = 2;
byte btn2 = 3;
byte btn3 = 4;
byte resetBtn = 5;
byte led = 13;

bool doOnce = false;
int counter = 0;
int myPins[] = {2, 4, 8, 3, 6};
int combo[] = { 0, 0, 0};
int correctCombo[] = {2, 4, 3};

void setup() {
  Serial.begin(9600);
  pinMode(2, INPUT);
  pinMode(3, INPUT);
  pinMode(4, INPUT);
  pinMode(5, INPUT);
  pinMode(13, OUTPUT);

  digitalWrite(led, LOW);
  digitalWrite(resetBtn, LOW);
}

void loop() {
  
  if(digitalRead(resetBtn) == HIGH){
    reset();
  }

  if(counter < 3){
    
    digitalWrite(led, LOW);
    
    if(digitalRead(btn1) == HIGH && !doOnce){
  
      combo[counter] = 2;
      counter++;
      
      Serial.print("Btn1 pressed. ");
      doOnce = true;
    }
    if(digitalRead(btn2) == HIGH && !doOnce){
  
      combo[counter] = 3;
      counter++;
      
      Serial.print("Btn2 pressed. ");
      doOnce = true;
    }
    if(digitalRead(btn3) == HIGH && !doOnce){
  
      combo[counter] = 4;
      counter++;
      
      Serial.print("Btn3 pressed. ");
      doOnce = true;
    }
  } else {
    if(combo[0] == correctCombo[0] && combo[1] == correctCombo[1] && combo[2] == correctCombo[2]){
      digitalWrite(led, HIGH);
      Serial.print("Combination succeeded! ");
    } else {
      reset();
      Serial.print("Combination failed. ");
    }
  }
  
  if(digitalRead(btn1) == LOW && digitalRead(btn2) == LOW && digitalRead(btn3) == LOW){
    doOnce = false;
  }

  if(counter == 3){
    
  }
}

void reset(){
  counter = 0;
    combo[0] = 0;
    combo[1] = 0;
    combo[2] = 0;
    Serial.print("Reset. ");
}

---

Analog In

Using an FSR and an RGB LED, I made a simple weight scale, consisting of a pad (regular perforated cardboard with the sensor stuffed in) that visualizes the weight of objects placed on top of it with the color of the LED — green being lightest, red being heaviest.

const int redLED = 11;
const int greenLED = 10;
const int blueLED = 9;
int sensorValue = 0;

void setup() {
  Serial.begin(9600);
  pinMode(redLED, OUTPUT);
  pinMode(greenLED, OUTPUT);
  pinMode(blueLED, OUTPUT);
}

void loop() {
  
  sensorValue = analogRead(A0); // read the pot value
  int brightness = map(sensorValue, 0, 1024, 255, 0);
  int brightness_g = map(sensorValue, 0, 1024, 0, 255);
  int brightness_r = map(sensorValue, 0, 1024, 255, 0);

  analogWrite(redLED, brightness_r);
  
  if(brightness == 255){
    analogWrite(greenLED, 255);
  } else {
    analogWrite(greenLED, brightness_g);
  }
  
  analogWrite(blueLED, 255);
}