/week six: sensors
    

# capacitive sensor
    

# ---------------------------------
  

i decided to use a capacitive sensor to measure the amount of water in a cup.

here is a link to the code that i used — though i did make a small correction in line 26, changing it to pinMode(tx_pin,OUTPUT);

i then rigged up the circuit as such:

i connected the alligator clips to the copper plates, which i taped to the sides of a cup. the two masking tape lines correspond to 50mL and 150mL of water, which i measured out prior to attaching the plates.

i began pouring in water and seeing the corresponding change in capacitance on the serial plotter, which i was able to calibrate due to the pre-measured quantities on the cup.

# piezo sensor
    

# ---------------------------------
  

having already implemented a piezo sensor for my week 4 assignment, i decided to add upon that setup by implementing a pattern-based knock recognition mechanism.

if you'll recall, the previous mechanism would activate after a single knock above a certain threshold.

for this week's assignment, my goal was to allow it to activate only after four knocks — one hard, two soft, and one hard.

this mainly required adjustments in the arduino code. this was my initial version:

  const int sensor = A0;     
  const int A1A = 3;
  const int A1B = 4;

  int sensorReading = 0;

  void setup() {
    pinMode(A1A, OUTPUT);
    pinMode(A1B, OUTPUT);
    digitalWrite(A1A, LOW);
    digitalWrite(A1B, LOW);
    Serial.begin(9600);
  }

  void loop() {
    sensorReading = analogRead(sensor);
    
    if (sensorReading >= 25) {
      digitalWrite(A1A, HIGH);
      Serial.println(sensorReading);
      delay(3000);
      digitalWrite(A1A, LOW);
      delay(3000);
      digitalWrite(A1B, HIGH);
      delay(3000);
      digitalWrite(A1B, LOW);
    }
  }

i soon discovered that if i wanted to implement a pattern-based system, i would have to create a variable that would track the number of knocks and create different if statements that corresponded to the number of knocks that have already been made. additionally, i would no longer be able to rely on the delay() function, and would have to use the millis() function to track time.

after several rounds of iterations around these constraints, here was my new version:

  const int sensor = A0;     
  const int A1A = 3;
  const int A1B = 4;
  
  int sensorReading = 0;
  int knocks = 0;         
  unsigned long previousTime = 0;
  
  long interval = 1000;
  
  void setup() {
    pinMode(A1A, OUTPUT);
    pinMode(A1B, OUTPUT);
    digitalWrite(A1A, LOW);
    digitalWrite(A1B, LOW);
      Serial.begin(9600);
  
  }
  
  void loop() {
    sensorReading = analogRead(sensor);
    unsigned long currentTime = millis();
  
    if (currentTime % 100){
      Serial.println(knocks);
    }
    
    if (sensorReading >= 100 and knocks == 0){
      knocks ++;
      previousTime = currentTime;
    } 
  
    if (knocks == 1 and currentTime - previousTime > interval and sensorReading >= 25){
      knocks ++;
      previousTime = currentTime;
    }
  
    if (knocks == 2 and currentTime - previousTime > interval and sensorReading >= 25){
      knocks ++;
      previousTime = currentTime;
    }
  
    if (knocks == 3 and currentTime - previousTime > interval and sensorReading >= 25){
     digitalWrite(A1A, HIGH);
      knocks ++;
      previousTime = currentTime;
    }
  
    if (knocks == 4 and currentTime - previousTime > 1000){
     digitalWrite(A1A, LOW);
      knocks = 0;
    }
  }

i then made some slight adjustments to condense the code/remove redundancies, and this was my final version:

  const int sensor = A0;     
const int A1A = 3;
const int A1B = 4;

int sensorReading = 0;
int k = 0;         
unsigned long previousTime = 0;

long interval = 500;

void setup() {
  pinMode(A1A, OUTPUT);
  pinMode(A1B, OUTPUT);
  digitalWrite(A1A, LOW);
  digitalWrite(A1B, LOW);
    Serial.begin(9600);

}

void loop() {
  sensorReading = analogRead(sensor);
  unsigned long currentTime = millis();
  Serial.println(k);

  if ((sensorReading >= 100 and k == 0) or ((k == 1 or k == 2) and currentTime - previousTime > interval and sensorReading >= 25)){
    k ++;
    previousTime = currentTime;
  }

  if (k == 3 and currentTime - previousTime > interval and sensorReading >= 100){
   digitalWrite(A1A, HIGH);
    k ++;
    previousTime = currentTime;
  }

  if (k == 4 and currentTime - previousTime > 1000){
   digitalWrite(A1A, LOW);
    k = 0;
  }
}

and after uploading it to the arduino board, here it is in action: