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Chassis Assembly

I attached the motors to the chassis and tested the directions of travel.

Then I soldered some wires to the leads of the motors for easier access.

I am using four 1.5V batteries (6V) as a power supply for the motors.

Motor Control System

After the motors where all attached and moving the correct direcion, I wired the L298 motor drivers along with the Arduino.

To test the first driver, I create a simple script to drive in forward then stop and then reverse

// ***************** PINS **********************
// Front Right Motor (FR)
int motorFRpin1 = 5;
int motorFRpin2 = 4;

// Front Left Motor (FL)
int motorFLpin1 = 3;
int motorFLpin2 = 2;
// ********************************************

void setup() {
  // Set all motor pins to output
  pinMode(motorFRpin1,OUTPUT);
  pinMode(motorFRpin2,OUTPUT);
  pinMode(motorFLpin1,OUTPUT);
  pinMode(motorFLpin2,OUTPUT);

}

void loop() {
  // Forward for 2 seconds
  digitalWrite(motorFRpin1, HIGH);
  digitalWrite(motorFRpin2, LOW);

  digitalWrite(motorFLpin1, HIGH);
  digitalWrite(motorFLpin2, LOW);
  delay(2000);

  // Stop for 1 sec
  digitalWrite(motorFRpin1, LOW);
  digitalWrite(motorFRpin2, LOW);

  digitalWrite(motorFLpin1, LOW);
  digitalWrite(motorFLpin2, LOW);
  delay(1000);

  // Reverse for 2 secs
  digitalWrite(motorFRpin1, LOW);
  digitalWrite(motorFRpin2, HIGH);

  digitalWrite(motorFLpin1, LOW);
  digitalWrite(motorFLpin2, HIGH);
  delay(2000);

}

When I was wiring the first motor driver and tested it with some simple Arduino code, I noticed the motors seem to pause on each loop

I suspect this is due to single 6V supply being insufficient for the Arduino, the motors and L298. This is why I added an extra 9V cell to supply the Arduino.

Ultrasonic Sensor

To mount the ultrasonic sensor, I couldn’t just pin it into the breadboard as that would just connect all of the pins together due to the orientation of the breadboard. So I decided to use male to female jumpers which I then ran through the chassis of the car towards the Arduino. This made me have to change the direction of travel, so I had to switch the pins in the Arduino code for the motors drivers.

I also made some adjustments to the code.

Added pins for the trigger and echo of the sensor

// Ultrasonic Sensor
#define Trigger 12
#define Echo 13

initial setup for correct i/o config

// Set Echo and Trigger for US Sensor
  pinMode(Echo, INPUT);
  pinMode(Trigger, OUTPUT);

added pulse and reading to the loop, plus I calculated distance and created a simple emergency stop logic

void loop() {
  // Set Trigger LOW
  digitalWrite(Trigger, LOW);
  delayMicroseconds(2);
  
  // Emit high frequency 40kHz sound pulse (i.e. pull the Trigger)
  digitalWrite(Trigger, HIGH);
  delayMicroseconds(10);
  digitalWrite(Trigger, LOW);

  // Detect a pulse
  int distance = pulseIn(Echo, HIGH);

  // Speed of sound is: 343 m/s -> 343 x 10^2 cm/s -> 343 x 10^2 x 10^-6 cm/us -> 29.15451895 us/cm
  distance = distance / 29 / 2;  // in cm
  // we divide by 2 to acount for the round trip
  
  // Driving Logic
  if (distance <= 10){
    // Emergency stop
    digitalWrite(FR_f, LOW);
    digitalWrite(FR_r, LOW);
    digitalWrite(FL_f, LOW);
    digitalWrite(FL_r, LOW);
    digitalWrite(RR_f, LOW);
    digitalWrite(RR_r, LOW);
    digitalWrite(RL_f, LOW);
    digitalWrite(RL_r, LOW);
  } else {
    // Forward Drive
    digitalWrite(FR_f, HIGH);
    digitalWrite(FR_r, LOW);
    digitalWrite(FL_f, HIGH);
    digitalWrite(FL_r, LOW);
    digitalWrite(RR_f, HIGH);
    digitalWrite(RR_r, LOW);
    digitalWrite(RL_f, HIGH);
    digitalWrite(RL_r, LOW);
  }
  // Print the distance in inches
  Serial.println(distance);
  
  // Pause for 100 milliseconds
  delay(200);
}

Final Result

Finally, I had a basic car that moves foward until it detects an obstacle within 10cm of the sensor.

Pin Connections

Arduino/Breadboard	Component	Comment
7	Front L298N IN1	Forward for Front Right Motor
6	Front L298N IN2	Reverse for Front Right Motor
9	Front L298N IN3	Forward for Front Left Motor
8	Front L298N IN4	Reverse for Front Left Motor
2	Rear L298N IN1	Forward for Rear Right Motor
3	Rear L298N IN2	Reverse for Rear Right Motor
4	Rear L298N IN3	Forward for Rear Left Motor
5	Rear L298N IN4	Reverse for Rear Left Motor
GND	Both L298N GND, Ultrasonic Sensor GND	Must GND L298N, Arduino, and power supply
5V	Rear L298N 5V	To power Arduino or vice-versa
Left Power Rail +	Front L298N 5V, Ultrasonic Sensor PWR	L298N outputs the 5V which powers the US sensor
Right Power Rail +	Both L298N 12V	To power the motor drivers
12	Ultrasonic Sensor Trigger	Input to send pulse
13	Ultrasonic Sensor Echo	Output of time for reception

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