28015 Ultrasonic Sensor returns 0 cm no matter what

[jungletemples]

I'm just starting out with Arduino so I copy-pasted the code from the ultrasonic sensors lesson and modified it to make a sensor+lcd combo that sends different messages based on the distance of an object. Unfortunately, it always returns 0 cm in the serial monitor no matter what I do. Here's the code (I know the text doesn't really make much sense at the moment but I'll iron that out):

// include the library code:

#include <LiquidCrystal.h>

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

int distanceThreshold;

int cm;

int inches;

long readUltrasonicDistance(int triggerPin, int echoPin)
{
  pinMode(triggerPin, OUTPUT);  // Clear the trigger
  digitalWrite(triggerPin, LOW);
  delayMicroseconds(2);
  // Sets the trigger pin to HIGH state for 10 microseconds
  digitalWrite(triggerPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(triggerPin, LOW);
  pinMode(echoPin, INPUT);
  // Reads the echo pin, and returns the sound wave travel time in microseconds
  return pulseIn(echoPin, HIGH);
}



void setup()

{
  Serial.begin(9600);
  // set up the LCD's number of columns and rows:
  lcd.begin(19, 2);
  // Print a message to the LCD.
  lcd.print("Welcome!");
  delay(500);
  lcd.clear();
      lcd.setCursor(4,0);
      lcd.print("Let's see!");    
  delay(500);
  lcd.clear();

}

void loop()
{
  
  distanceThreshold = 350;
  cm = 0.01723 * readUltrasonicDistance(7, 7);
  inches = (cm / 2.54);
  Serial.print(cm);
  Serial.print("cm, ");
  Serial.print(inches);
  Serial.println("in");
  if (cm > distanceThreshold) {
    lcd.print("You cannot be detected. Please stand closer");
    lcd.setCursor(2,1);
    lcd.print("? units away");
    delay(1500);
    lcd.clear();
    lcd.setCursor(4,0);
  }
  if (cm <= distanceThreshold && cm > distanceThreshold - 100) {
    lcd.print("Step MUCH closer!");
 lcd.print(cm);
  
  }
  if (cm <= distanceThreshold - 100 && cm > distanceThreshold - 250) {
    lcd.print("A bit too far!");
    lcd.setCursor(2,1);
    lcd.print(cm);
  
  }
  if (cm <= distanceThreshold - 250 && cm > distanceThreshold - 350) {
    lcd.print("Perfect");
    lcd.setCursor(2,1);
    lcd.print(cm);

  }
  if (cm <= distanceThreshold - 350) {
    lcd.print("Way too close!");
    lcd.setCursor(2,1);
    lcd.print(cm);
    lcd.setCursor(2,1);
    lcd.print("? units away");
    delay(1500);
    lcd.clear();
    lcd.setCursor(4,0);
  }
    delay(100); // Wait for 100 millisecond(s)
}
 

And here's an image:

Any help with making it work as intended would be very appreciated!

[markd833]

As a starting point, did the original code from the ultrasonic sensors lesson work for you?

[jungletemples]

Yes it did print the correct distances in the serial monitor, but I changed something, and I can't remember what, but it was probably the if statements, and it broke the readings Here's the original code which was barely modified by me for reference. It lit leds connected to pins 2,3, and 4 based on distance. I removed the unnecessary led functionality, so that probably is a factor as well.

int distanceThreshold = 0;

int cm = 0;

int inches = 0;

long readUltrasonicDistance(int triggerPin, int echoPin)
{
  pinMode(triggerPin, OUTPUT);  // Clear the trigger
  digitalWrite(triggerPin, LOW);
  delayMicroseconds(2);
  // Sets the trigger pin to HIGH state for 10 microseconds
  digitalWrite(triggerPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(triggerPin, LOW);
  pinMode(echoPin, INPUT);
  // Reads the echo pin, and returns the sound wave travel time in microseconds
  return pulseIn(echoPin, HIGH);
}

void setup()
{
  Serial.begin(9600);

  pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);
  pinMode(4, OUTPUT);
}

void loop()
{
  // set threshold distance to activate LEDs
  distanceThreshold = 350;
  // measure the ping time in cm
  cm = 0.01723 * readUltrasonicDistance(7, 7);
  // convert to inches by dividing by 2.54
  inches = (cm / 2.54);
  Serial.print(cm);
  Serial.print("cm, ");
  Serial.print(inches);
  Serial.println("in");
  if (cm > distanceThreshold) {
    digitalWrite(2, LOW);
    digitalWrite(3, LOW);
    digitalWrite(4, LOW);
  }
  if (cm <= distanceThreshold && cm > distanceThreshold - 100) {
    digitalWrite(2, HIGH);
    digitalWrite(3, LOW);
    digitalWrite(4, LOW);
  }
  if (cm <= distanceThreshold - 100 && cm > distanceThreshold - 250) {
    digitalWrite(2, HIGH);
    digitalWrite(3, HIGH);
    digitalWrite(4, LOW);
  }
  if (cm <= distanceThreshold - 250 && cm > distanceThreshold - 350) {
    digitalWrite(2, HIGH);
    digitalWrite(3, HIGH);
    digitalWrite(4, HIGH);
  }
  if (cm <= distanceThreshold - 350) {
    digitalWrite(2, HIGH);
    digitalWrite(3, HIGH);
    digitalWrite(4, HIGH);
  }
  delay(100); // Wait for 100 millisecond(s)
}

[Paul_KD7HB]

That should be a clue to start over and don't remove code, just mark it as a comment.

[ruilviana]

Hi @jungletemples

There is a basic error in the two codes you posted:
Every calculation using values with decimal places the variable must be of type float.
Instead of "int cm;" and "int inches;" use "float cm; and "float inches;".

[jungletemples]

This worked perfectly! Thanks so much