Getting SR04 sensor to run motor at zero cm

Projects Programming
1

So I can get my code to run a motor at greater than 20 cm and not run at less than 20 cm the problem is that if the sensor can't read a distance because it is to far away it returns 0 as the distance. I am trying to get the motor to run then at 0 and at greater than 20 but with no luck. Here is my latest try which ended up still turning the motor off at 0 which I think is because the first if statement just cancels out the left else if statement. Is there a way to set it to turn off for an interval of distance?

#include <NewPing.h>
#define TRIGGER_PIN 11
#define ECHO_PIN 12
#define MAX_DISTANCE 50 //max distance to ping for
NewPing sonar(TRIGGER_PIN, ECHO_PIN, MAX_DISTANCE);
const int rightMotor1 = 6;
const int rightMotor2 = 7;
const int enablePin = 9;
void setup() 
{
  Serial.begin(9600);
  pinMode(rightMotor1, OUTPUT);
  pinMode(rightMotor2,OUTPUT);
  pinMode(enablePin, OUTPUT);
  digitalWrite(enablePin, LOW);
}

void loop() 
{
  delay(50);
  unsigned int uS = sonar.ping();
  int distance = sonar.ping_cm();
  Serial.print("Ping: ");
  Serial.print(uS / US_ROUNDTRIP_CM);
  Serial.println("cm");
  if(distance < 20)
  {
  digitalWrite(enablePin, LOW);
  }
  else if(distance > 20) 
  {
    digitalWrite(enablePin, HIGH);
    digitalWrite(rightMotor1, HIGH);
    digitalWrite(rightMotor2, LOW);
  }
  else if(distance == 0)
  {
    digitalWrite(enablePin, HIGH);
    digitalWrite(rightMotor1, HIGH);
    digitalWrite(rightMotor2, LOW);
  }
}
2 
  if(distance < 20)
  {
  digitalWrite(enablePin, LOW);
  }
  else if(distance > 20)
  {
    digitalWrite(enablePin, HIGH);
    digitalWrite(rightMotor1, HIGH);
    digitalWrite(rightMotor2, LOW);
  }
  else if(distance == 0)

Isn't 0 less than 20?

3

That's what I meant by I though they were canceling each other out, but I don't know how I could get the first if statement to look for an interval of 1-20 so that it wouldn't account for the 0. I'm just wondering if that is possible?

4 
if (distance > 20) || (distance == 0)
{
yadayadayada
}

If (distance >= 1) && (distance <= 20)
{
yadayadayda
}
5

I am now getting this error "exit status 1" and "expected primary-expression before '||' token

  if(distance > 20) || (distance == 0)
  {
  digitalWrite(enablePin, HIGH);
  digitalWrite(rightMotor1, HIGH);
  digitalWrite(rightMotor2, LOW);
  }
  else if(distance >= 1) && (distance < 20)
  { 
    digitalWrite(enablePin, LOW);
  }
}
6 
if((distance > 20) || (distance == 0))
else if((distance >= 1) && (distance < 20)) // Forgot this one a moment ago.

Edit: I would have done it a little differently, but deleted my post since nzcrog's was similar.

7

If you start with the most restrictive case first, and move on to less restrictive cases, everything will work:

if(distance == 0) // Very restrictive
{
}
else if(distance < 20) // Not as restrictive, since the range is bound on one end only
{
}
else // Handle any distance greater than 20
{
}