How to Program a Smart Car Key Fob: Understanding the Basics with Arduino Projects

While “programming a smart car key fob” might conjure images of complex automotive systems, the fundamental principles can be explored and understood through simpler, hands-on projects. For enthusiasts and learners, diving into DIY electronics projects like building a remote-controlled car using Arduino offers an accessible entry point into the world of automotive control systems.

This guide will walk you through the basics of remote control using an Arduino project, drawing inspiration from a common challenge faced by beginners: controlling a remote car. Although we won’t be directly programming a modern car key fob, this project will illuminate the underlying concepts of signal transmission, reception, and command execution that are crucial in understanding how key fobs and other automotive control systems work. By the end, you’ll have a clearer picture of the logic behind remote control and potentially diagnose issues in your own projects.

Decoding the Remote Control: An Arduino Car Project

Let’s consider a scenario where you’re building an Elegoo car for a class project and encounter a common hurdle: getting the remote control to work correctly. Many beginners, when starting with IR remote control for Arduino cars, might face issues where only some functionalities work as expected. A typical problem is that one side of the car’s wheels doesn’t respond, even though the motors seem fine.

Let’s examine a sample Arduino code designed for an IR remote controlled car to understand the process and troubleshoot potential problems.

#include <IRremote.h>

#define F 16736925
#define B 16754775
#define L 16720605
#define R 16761405
#define S 16712445
#define UNKNOWN_F 5316027
#define UNKNOWN_B 2747854299
#define UNKNOWN_L 1386468383
#define UNKNOWN_R 553536955
#define UNKNOWN_S 3622325019

int RECV_PIN = 12;
int in1=6;
int in2=7;
int in3=8;
int in4=9;
int ENA=5;
int ENB=11;
int ABS=250;

IRrecv irrecv(RECV_PIN);
decode_results results;
unsigned long val;

void _mForward() {
  analogWrite(ENA,ABS);
  analogWrite(ENB,ABS);
  digitalWrite(in1,HIGH);//digital output
  digitalWrite(in2,LOW);
  digitalWrite(in3,HIGH);
  digitalWrite(in4,HIGH);
  Serial.println("go forward!");
}
void _mBack() {
  analogWrite(ENA,ABS);
  analogWrite(ENB,ABS);
  digitalWrite(in1,LOW);
  digitalWrite(in2,HIGH);
  digitalWrite(in3,LOW);
  digitalWrite(in4,HIGH);
  Serial.println("go back!");
}
void _mleft() {
  analogWrite(ENA,ABS);
  analogWrite(ENB,ABS);
  digitalWrite(in1,HIGH);
  digitalWrite(in2,LOW);
  digitalWrite(in3,HIGH);
  digitalWrite(in4,LOW);
  Serial.println("go left!");
}
void _mright() {
  analogWrite(ENA,ABS);
  analogWrite(ENB,ABS);
  digitalWrite(in1,LOW);
  digitalWrite(in2,HIGH);
  digitalWrite(in3,LOW);
  digitalWrite(in1,LOW); // Typo in original code, should be in3 for right side motor control
  digitalWrite(in4,HIGH);
  Serial.println("go right!");
}
void _mStop() {
  digitalWrite(ENA,LOW);
  digitalWrite(ENB,LOW);
  Serial.println("STOP!");
}

void setup() {
  pinMode(in1,OUTPUT);
  pinMode(in2,OUTPUT);
  pinMode(in3,OUTPUT);
  pinMode(in4,OUTPUT);
  pinMode(ENA,OUTPUT);
  pinMode(ENB,OUTPUT);
  _mStop();
  irrecv.enableIRIn();
  Serial.begin(9600);
}

void loop() {
  if (irrecv.decode(&results)){
    val = results.value;
    Serial.println(val);
    irrecv.resume();
    switch(val){
      case F:
      case UNKNOWN_F:
        _mForward();break;
      case B:
      case UNKNOWN_B:
        _mBack(); break;
      case L:
      case UNKNOWN_L:
        _mleft(); break;
      case R:
      case UNKNOWN_R:
        _mright();break;
      case S:
      case UNKNOWN_S:
        _mStop(); break;
      default:break;
    }
  }
}

Breaking Down the Code

This code is designed to control a two-motor car using an IR remote. Let’s dissect it part by part:

• Include Libraries and Define Constants: #include <IRremote.h> imports the necessary library for IR remote control. The #define statements assign names to specific numerical codes received from the IR remote for different commands like Forward (F), Backward (B), Left (L), Right (R), and Stop (S). The UNKNOWN_ constants are likely for handling potential variations in remote codes or for debugging.

• Pin Definitions: This section assigns Arduino pins to motor control functions. in1, in2, in3, in4 are control pins for the motor driver, while ENA and ENB are enable pins that control motor speed using PWM (Pulse Width Modulation) via analogWrite. RECV_PIN (pin 12) is where the IR receiver is connected to the Arduino.

• IR Receiver Setup: IRrecv irrecv(RECV_PIN); initializes the IR receiver object. decode_results results; and unsigned long val; are variables to store the decoded IR signals.

• Motor Control Functions:

  • _mForward(), _mBack(), _mleft(), _mright(), _mStop(): These functions define the actions for each direction and stop. They use digitalWrite() to control the direction of current flow through the motors via pins in1 – in4, and analogWrite() to set motor speed via ENA and ENB. Notice that in the original _mright() function, there’s a likely typo: digitalWrite(in1,LOW); should probably be digitalWrite(in3,LOW); to control the right side motor correctly.

• setup() Function: This runs once at the start. It sets the defined pins as OUTPUT, initializes the motor to stop using _mStop(), enables the IR receiver, and starts serial communication for debugging.

• loop() Function: This runs continuously. irrecv.decode(&results) checks if an IR signal is received and decodes it. If a signal is decoded, val = results.value; stores the received value. The switch(val) statement then compares the received value with the defined command codes (F, B, L, R, S) and calls the corresponding motor control function. irrecv.resume(); prepares the IR receiver to receive the next signal.

Troubleshooting: Why Is Only One Side Working?

The original problem statement mentions that only the left wheels were working. Based on the code and common beginner mistakes, here are a few troubleshooting steps:

1. Code Review – The Typo: Examine the _mright() function closely. The original code snippet has digitalWrite(in1,LOW); twice, instead of controlling both motors for a right turn. It should likely be:

   void _mright() {
     analogWrite(ENA,ABS);
     analogWrite(ENB,ABS);
     digitalWrite(in1,LOW);
     digitalWrite(in2,HIGH);
     digitalWrite(in3,LOW); // Corrected line - control right motor direction pin
     digitalWrite(in4,HIGH);
     Serial.println("go right!");
   }

   Correcting this typo in your code is the first and most crucial step.

2. Wiring Check: Double-check the wiring of your motor driver to the Arduino and to the motors themselves. Ensure that pins in1, in2, in3, in4, ENA, and ENB are connected to the correct Arduino pins as defined in the code. Verify that the motor connections are secure and correctly oriented. Sometimes, motor wires might be swapped, causing unexpected behavior.

3. Motor Driver Functionality: Test each motor and motor driver channel independently. You can do this by:

   • Disconnecting one motor at a time and testing if the other motor responds correctly to forward/backward commands.
   • Swapping motor connections on the driver to see if the issue shifts to the other side, indicating a problem with a specific motor driver channel or motor.

4. Power Supply: Ensure that your Arduino and motor driver are receiving sufficient power. Motors, especially when starting or under load, can draw significant current. An inadequate power supply can lead to erratic behavior or one side of the motor not functioning correctly.

5. IR Remote and Receiver Functionality: While less likely if some commands are working, ensure your IR remote batteries are good and the IR receiver is functioning correctly. You can test the IR receiver by monitoring the serial output. Every button press on the remote should result in a different numerical value being printed in the serial monitor. If no values are being printed, there might be an issue with the IR receiver or its connection.

From Toy Cars to Smart Key Fobs: The Underlying Principle

While this project deals with a toy car, the core principle of sending a signal (from the remote), receiving it (by the IR receiver), decoding it (by the Arduino), and then executing a command (motor control) is fundamental to many wireless control systems, including smart car key fobs.

Smart key fobs use radio frequencies instead of infrared, and the communication is significantly more complex, involving encryption and security protocols. However, the basic idea remains the same: pressing a button on the fob sends a coded signal to the car. The car’s computer receives and validates this signal before executing actions like unlocking doors, starting the engine, or activating the alarm.

Understanding these basic Arduino projects provides a stepping stone to grasping the intricacies of modern automotive electronics. By troubleshooting and modifying this simple remote car project, you gain valuable insights into how signals, code, and hardware interact to create functional control systems – a principle that extends to the “programming” of sophisticated devices like smart car key fobs.

By correcting the potential typo in the _mright() function and methodically checking the wiring and components, you should be able to get your Elegoo car project working correctly and gain a deeper understanding of remote control principles applicable far beyond just toy cars.