[SOLVED] URM37 Sensor 'lags'?

Projects Programming
1

Hi everybody,

I recently started using arduino and I wanted to make an obstacle avoiding robot as a first robot project..
I know how to drive the motors and how to measure distance, and both of them workt great..

But when I combine the codes, the distance measuring starts to 'lag' and returns 0cm distance randomly between other distances..

I use this code..

int URPWM=3;                                        // PWM Output 0-25000us,every 50us represent 1cm
int URTRIG=5;                                       // PWM trigger pin
unsigned long time;                                 // create a time variable
unsigned long urmTimer = 0;                         // timer for managing the sensor reading flash rate
 
unsigned int Distance=0;
uint8_t EnPwmCmd[4]={0x44,0x22,0xbb,0x01};          // distance measure command
 
int E1 = 5;
int M1 = 4;
int E2 = 6;
int M2 = 7;
 
void setup(){                                      // Serial initialization
  Serial.begin(9600);                              // Sets the baud rate to 9600
  
  pinMode(M1, OUTPUT);
  pinMode(M2, OUTPUT);
  
  PWM_Mode_Setup();
}
 
void loop(){   
   if(millis()-time>=20){                           // interval 0.02 seconds
     time=millis();                                 // get the current time of program
   }
   
   if(millis()-urmTimer>50){
     urmTimer=millis(); 
     PWM_Mode();
   }
 }
 
 void PWM_Mode_Setup(){ 
  pinMode(URTRIG,OUTPUT);                            // A low pull on pin COMP/TRIG
  digitalWrite(URTRIG,HIGH);                         // Set to HIGH
  
  pinMode(URPWM, INPUT);                             // Sending Enable PWM mode command
  
  for(int i=0;i<4;i++){
      Serial.write(EnPwmCmd[i]);
   } 
}
 
void PWM_Mode(){                                     // a low pull on pin COMP/TRIG  triggering a sensor reading
    digitalWrite(URTRIG, LOW); 
    digitalWrite(URTRIG, HIGH);                      // reading Pin PWM will output pulses
     
    unsigned long DistanceMeasured=pulseIn(URPWM,LOW);
     
    if(DistanceMeasured==50000){                     // the reading is invalid.
      Serial.print("Invalid");    
   }
    else{
      Distance=DistanceMeasured/50;                  // every 50us low level stands for 1cm
      
    if(Distance > 15){
        digitalWrite(M1, HIGH);
        digitalWrite(M2, HIGH);
        analogWrite(E1, 150);
        analogWrite(E2, 150);
      } else {
        digitalWrite(M1, LOW);
        digitalWrite(M2, LOW);
        analogWrite(E1, 150);
        analogWrite(E2, 150);
      }
   }
  Serial.print("Distance=");
  Serial.print(Distance);
  Serial.println("cm");
  
}

and it it always prints this:
Distance = right distance
Distance = 0
Distance = right distance
Distance = 0
Distance = right distance
Distance = 0
etc..

But if I remove the if(distance > 15){ //code } else {//code }, then it just works fine..
Does anybody know what's wrong?

ps. The motor drive isn't wrong.. It just drives forward or backward.. I already tested that in a seperate sketch..
pps. The measuring code comes from dfrobot wiki

2

What do the E1 and E2 do ?

3

MSquare, they define the speed.. (0 = not moving, 255 = full speed)

4

Ok.. I already found it.. I defined pin 5 twice...

5

I'm not familiar with that type of transducer but I would expect to need to control the duration of the pulse to trigger the 'ping', and also to have a brief delay after sending and before waiting for the echo to ensure the transducer has settled after the ping. So I suggest you stick a brief delay() or delayMicroseconds() before and after the call to digitalWrite(URTRIG, HIGH) on line 47.

Also, I guess those calls outputting to M1, M2, E1, E2 may be driving a motor. In that case I suggest you try disconnecting the motor(s) and see whether that cures the problem - they may be causing electrical or mechanical noise which interferes with the ultrasonic transducer.