Electronic – arduino – Basic Robotics Help. Variable motor speed control by ultrasonic sensor input on arduino

First, thank you for taking the time to read my post.

I am attempting to use an ultrasonic sensor to control a DC motor using the PWM output of an arduino. Fairly simple, I know, but I'm just a beginner. 🙂

Here's my code, with an explanation of my theory and my error afterwards.

#define trigPin 7
#define echoPin 2
#define motorPin 9

void setup(){
 Serial.begin(9600);
 pinMode(trigPin, OUTPUT);
 pinMode(echoPin, INPUT);
 pinMode(motorPin, OUTPUT);
}

void loop(){
  int duration, distance;
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(1000);
  digitalWrite(trigPin, LOW);
  duration = pulseIn(echoPin, HIGH); 
  distance = (duration/2) /29.1; 
  if (distance <5)
  {
    analogWrite(motorPin, 0);
  }
  else if(5 <= distance <15)
  {
    analogWrite(motorPin, 50);
  }
  else if(15 <= distance <25)
  {
    analogWrite(motorPin, 100);
  }
  else if(25 <= distance < 35)
  {
    analogWrite(motorPin, 150);
  }
  else if(35 <= distance < 45)
  {
    analogWrite(motorPin, 200);
  }
  else if(45 <= distance)
  {
    analogWrite(motorPin, 255);
  }
  else;
  {
    analogWrite(motorPin, 0);
  }
  Serial.print (distance);
  Serial.println (" cm");
  delay(500);
}

So, this is incredibly simple. I haven't yet begun differential drive nor braking, and soon I want to learn to change out the ultrasonic sensor programming with the NewPing library for more sensors and less delay.

Right now, I am hoping to have the arduino interpret the ultrasonic ping as a distance in centimeters and based of that distance set the DC motor to a defined speed. The PWM output goes to a 210 Ohm resistor connected to the base pin of a transistor, on the collector/emitter is the 18V circuit connected to the DC motor. On a separate circuit is the arduino and ultrasonic sensor.

The circuit successfully gives me accurate distances in the serial monitor window. However, the motor only goes at 100% speed. It does not throttle its speed regardless of the distance variable's value.

It startles me that the default motor speed for this setup is 100%, it makes me think the speed is acting digitally. I tried deleting the final elseif conditional for the distance being greater than 45 cm set speed at 100% and the circuit still powered the motor at 100%.

Any help would be greatly appreciated!