Vex Ultrasonic Range Finder

Using Arduino Sensors
5

I have hooked up the sensor (see the image) and written some very bare bones code. Essentially all the code really does is set pin 13 high for a short period of time and then polls pin 10. Pin 10 goes high instantly (for three cycles of the loop) and then stays low forever. I expected pin 10 to be low initially and then go high for a very short period of time and then low again.

Any ideas what I'm doing wrong here?

/*
Uses the Vex Range Finder in conjunction with 
Arduino Mega 2560
Pin 13 Triggers the Pulse (Yellow lead)
Pin 10 Recieves the Echo  (Orange lead)
*/

const int pulse_pin =  13;   // pin for triggering pulse
const int echo_pin = 10;     // pin for recieving echo
int pulse_state ; // 0 (no pulse recieved) 1 (pulse recieved)
int port_10_value;


void setup() {
  Serial.begin(9600);
  Serial.println ("Starting");
  // initialize the pulse pin as output:
  pinMode(pulse_pin, OUTPUT);      
  // initialize the echo_pin pin as an input:
  pinMode(echo_pin, INPUT);     
  
  //test code to be removed
}

void loop(){
   pulse_state = 0;
    port_10_value = 0;
    digitalWrite(pulse_pin, LOW);
    delayMicroseconds(2);

    digitalWrite(pulse_pin, HIGH); // send the pulse
    delayMicroseconds(5);
    digitalWrite(pulse_pin, LOW);  //wait and shut it down

  
    Serial.println("in main loop");
    
   while (pulse_state==0)
   {
      port_10_value = digitalRead (echo_pin);
      Serial.println("port 10 value");
      Serial.println(port_10_value,DEC);
      // will stay here forever because pulse_state is not changed
   }

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