2WD robot - logic error I am making a basic 2WD robot using Arduino Uno with motor shield.
I am getting no compile errors - but something in my logic flow is not working as expected.

Expected Operation:


Ping sensor does distance check.
If distance is less than 5cm.
Turn both Channel A &amp; B motors half-speed for 1 second.
Stop motors.
Take new distance reading ping, start again.


What however is happening, is that channel A works as expected, but channel B motor keeps running??
Where is my code / logic mistake?

Later date I will add to else statement to turn one wheel to change direction.

/*
 HC-SR04 Ping distance sensor:
 VCC to arduino 5v 
 GND to arduino GND
 Echo to Arduino pin 7 
 Trig to Arduino pin 8
 */

#define echoPin 7 // Echo Pin
#define trigPin 8 // Trigger Pin
#define LEDPin 13 // Onboard LED

int maximumRange = 1000; // Maximum range needed
int minimumRange = 1; // Minimum range needed
long duration, distance; // Duration used to calculate distance

void setup() {
  // put your setup code here, to run once:

Serial.begin (9600);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(LEDPin, OUTPUT); // Use LED indicator (if required)


  pinMode(12, OUTPUT); /* Motor Channel A RIGHT SIDE*/
  pinMode(9, OUTPUT); /* Motor Channel A */

  pinMode(13, OUTPUT); /* Motor Channel B LEFT SIDE */
  pinMode(8, OUTPUT);

  }

void loop() {


  /* Distance check begins */

  digitalWrite(trigPin, LOW); 
  delayMicroseconds(2); 

  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10); 

  digitalWrite(trigPin, LOW);

  duration = pulseIn(echoPin, HIGH);

 //Calculate the distance (in cm) based on the speed of sound.
 distance = duration/58.2;

 /* End distance check */

 if (distance &gt;= 5){
 /* Distance great enough to provide room to move */
  Serial.println("Move!");

  digitalWrite(LEDPin, HIGH); /* LED show movement */

  digitalWrite(12, LOW); /*move channel A motor half-speed */
  digitalWrite(9, LOW);
  analogWrite(3, 123);

  digitalWrite(13, HIGH); /*move channel B motor half-speed */
  digitalWrite(8, LOW);
  analogWrite(11, 123); 

  delay(1000);

  digitalWrite(9, HIGH); 
  digitalWrite(8, HIGH);
 }

 else {
 /* Send the distance to the computer using Serial protocol, and
 turn LED OFF to indicate successful reading. */
 Serial.println(distance);
 digitalWrite(LEDPin, LOW); 
 }

 //Delay 50ms before next reading.
 delay(500); 

}
I believe that your error is in that you declare LEDpin as pin 13 and then your motor B as pin 13 as well, that to me would result in errors when you write to the led in the else statement at the end of your code. I would recommend that you clean this up, don't use pins for different things. Try this first.

Your logic is ok in terms of functionality.

Also why is there inconsistency at this part on your code:

digitalWrite(12, LOW); /*move channel A motor half-speed */
  digitalWrite(9, LOW);
  analogWrite(3, 123);

  digitalWrite(13, HIGH); /*move channel B motor half-speed */
 digitalWrite(8, LOW);
  analogWrite(11, 123);


Why do you say pin 12 must beLOW and 13 HIGH when moving forward? Is this the way your un-mentioned circuit setup works, if possible could you add this info?