Hi friends,

Its first time for this 17 year old boy in here so please excuse me if there are any Mistakes
Your suggestion and comments are greatly appreciated

Here I am to share my experience-to add few components to your remote control car to control it using Any Android that can download apps and has bluetooth.

Here we are going to create a car that can be controlled using using Your android device

Requirements are the following ,

A very little knowledge about Arduino IDE software and coding + PC or Android device +

(everything is available in Amazon),

A remote control car (In this case two wheel drive car) =7$

(you can use any '6' AA 1.5v batteries) '6' Rechargeable batteries+charger=24$

HC05 bluetooth =8$

Arduino UNO R3 =25$

(H bridge) IC L293D =3$

USB cable (to connect from computer to arduino)=3$

Otg(if u wish to use android to upload sketches)=3$

LED's+wire(in this case some" female to male "and "male to male" wires)=10$

Solder+lead+paste=4$

(optional)Multimeter=3$

TOTAL=87$

Step 1: Why We Need This IC?

Two reasons;

1) The supply current of Arduino UNO board is low to run motors

2) you cannot reverse the direction of rotation of motor

I tried using NPN transistors as electronic switch to reverse the direction of current in motors but it couldn't bear the current and it screwed up (BAM !)

This IC can control 2 motors

So IC L293D has 16 pins ,the Vss pin is connected to 5v of arduino( condition Vss input min 4.5v)

Vs pin to the + terminal of battery powering motors (condition 36v>Vs input>Vss input )

(It can hold upto 600amps)

the GND pins are connected to the - terminal of the battery and the gnd pin of arduino are connected together to these pins

Pins 3,6 to terminals of one motor 14,11 to terminals of another motor

Pin 2,9 called enable pins .By varying the voltage between 0 to Vss you can control the speed of motor

so connect it to PWM output pins in arduino (ex. pin 2 for motor in PIN 3,6 )

Giving high input to pin 2 rotates the 3,6 motor in one direction and giving high input to pin 7 rotates it in other direction so simply connect it to digital output pins

Giving high input to pin 15 rotates the 14,11 motor in one direction and giving high input to pin 10 rotates it in other direction so simply connect it to digital output pins

YOU can use one battery source for running both Arduino board and IC L293D

I bought a IC with adapter as its easy to use .

Step 2: Programming Your Arduino UNO

Now ur ready to go but u need to setup your arduino to perform tricks

In this case i used an app called Bluetooth commander available in google play.The demo sketch is available in description column.

Another app called Android Bluetooth google play is very easy to use as u can use it directly only difference is that the former can control speed of car .So I prefer to the first one,

Download the app and the demo sketch

it looks like this

#define VERSION     "\n\nAndroTest V2.0 - @kas2014\ndemo for V5.X App (6 button version)"
// V2.0  changed to pure ASCII Communication Protocol ** not backward compatible **
// V1.4  improved communication errors handling
// V1.3  renamed for publishing, posted on 09/05/2014
// V1.2  Text display   ** not backward compatible **
// V1.1  Integer display
// V1.0  6 buttons + 4 data char implemented
// Demo setup:
// Button #1 controls pin #13 LED
// Button #4 toggle datafield display rate
// Button #5 configured as "push" button (momentary)
// Other buttons display demo message
// Arduino pin#2 to TX BlueTooth module
// Arduino pin#3 to RX BlueTooth module
// make sure your BT board is set @57600 bps
// better remove SoftSerial for PWM based projects
// For Mega 2560:
// remove   #include "SoftwareSerial.h", SoftwareSerial mySerial(2,3);
// search/replace  mySerial  >> Serial1
// pin#18 to RX bluetooth module, pin#19 to TX bluetooth module
#include "SoftwareSerial.h"
#define    STX          0x02
#define    ETX          0x03
#define    ledPin       13
#define    SLOW         750                            // Datafields refresh rate (ms)
#define    FAST         250                             // Datafields refresh rate (ms)
SoftwareSerial mySerial(2,3);                           // BlueTooth module: pin#2=TX pin#3=RX
byte cmd[8] = {0, 0, 0, 0, 0, 0, 0, 0};                 // bytes received
byte buttonStatus = 0;                                  // first Byte sent to Android device
long previousMillis = 0;                                // will store last time Buttons status was updated
long sendInterval = SLOW;                               // interval between Buttons status transmission (milliseconds)
String displayStatus = "xxxx";                          // message to Android device
void setup()  {
  Serial.begin(57600);
  mySerial.begin(57600);                                // 57600 = max value for softserial
  pinMode(ledPin, OUTPUT);     
  Serial.println(VERSION);
  while(mySerial.available())  mySerial.read();         // empty RX buffer
}
void loop() {
  if(mySerial.available())  {                           // data received from smartphone
    delay(2);
    cmd[0] =  mySerial.read();  
    if(cmd[0] == STX)  {
      int i=1;      
      while(mySerial.available())  {
        delay(1);
        cmd[i] = mySerial.read();
        if(cmd[i]>127 || i>7)                 break;     // Communication error
        if((cmd[i]==ETX) && (i==2 || i==7))   break;     // Button or Joystick data
        i++;
      }
      if     (i==2)          getButtonState(cmd[1]);    // 3 Bytes  ex: < STX "C" ETX >
      else if(i==7)          getJoystickState(cmd);     // 6 Bytes  ex: < STX "200" "180" ETX >
    }
  } 
  sendBlueToothData(); 
}
void sendBlueToothData()  {
  static long previousMillis = 0;                             
  long currentMillis = millis();
  if(currentMillis - previousMillis > sendInterval) {   // send data back to smartphone
    previousMillis = currentMillis; 
// Data frame transmitted back from Arduino to Android device:
// < 0X02   Buttons state   0X01   DataField#1   0x04   DataField#2   0x05   DataField#3    0x03 >  
// < 0X02      "01011"      0X01     "120.00"    0x04     "-4500"     0x05  "Motor enabled" 0x03 >    // example
    mySerial.print((char)STX);                                             // Start of Transmission
    mySerial.print(getButtonStatusString());  mySerial.print((char)0x1);   // buttons status feedback
    mySerial.print(GetdataInt1());            mySerial.print((char)0x4);   // datafield #1
    mySerial.print(GetdataFloat2());          mySerial.print((char)0x5);   // datafield #2
    mySerial.print(displayStatus);                                         // datafield #3
    mySerial.print((char)ETX);                                             // End of Transmission
  }  
}
String getButtonStatusString()  {
  String bStatus = "";
  for(int i=0; i<6; i++)  {
    if(buttonStatus & (B100000 >>i))      bStatus += "1";
    else                                  bStatus += "0";
  }
  return bStatus;
}
int GetdataInt1()  {              // Data dummy values sent to Android device for demo purpose
  static int i= -30;              // Replace with your own code
  i ++;
  if(i >0)    i = -30;
  return i;  
}
float GetdataFloat2()  {           // Data dummy values sent to Android device for demo purpose
  static float i=50;               // Replace with your own code
  i-=.5;
  if(i <-50)    i = 50;
  return i;  
}
void getJoystickState(byte data[8])    {
  int joyX = (data[1]-48)*100 + (data[2]-48)*10 + (data[3]-48);       // obtain the Int from the ASCII representation
  int joyY = (data[4]-48)*100 + (data[5]-48)*10 + (data[6]-48);
  joyX = joyX - 200;                                                  // Offset to avoid
  joyY = joyY - 200;                                                  // transmitting negative numbers
  if(joyX<-100 || joyX>100 || joyY<-100 || joyY>100)     return;      // commmunication error
  
// Your code here ...
    Serial.print("Joystick position:  ");
    Serial.print(joyX);  
    Serial.print(", ");  
    Serial.println(joyY); 
}
void getButtonState(int bStatus)  {
  switch (bStatus) {
// -----------------  BUTTON #1  -----------------------
    case 'A':
      buttonStatus |= B000001;        // ON
      Serial.println("\n** Button_1: ON **");
      // your code...      
      displayStatus = "LED ";
      Serial.println(displayStatus);
      digitalWrite(ledPin, HIGH);
      break;
    case 'B':
      buttonStatus &= B111110;        // OFF
      Serial.println("\n** Button_1: OFF **");
      // your code...      
      displayStatus = "LED ";
      Serial.println(displayStatus);
      digitalWrite(ledPin, LOW);
      break;
// -----------------  BUTTON #2  -----------------------
    case 'C':
      buttonStatus |= B000010;        // ON
      Serial.println("\n** Button_2: ON **");
      // your code...      
      displayStatus = "Button2 ";
      Serial.println(displayStatus);
      break;
    case 'D':
      buttonStatus &= B111101;        // OFF
      Serial.println("\n** Button_2: OFF **");
      // your code...      
      displayStatus = "Button2 ";
      Serial.println(displayStatus);
      break;
// -----------------  BUTTON #3  -----------------------
    case 'E':
      buttonStatus |= B000100;        // ON
      Serial.println("\n** Button_3: ON **");
      // your code...      
      displayStatus = "Motor #1 enabled"; // Demo text message
      Serial.println(displayStatus);
      break;
    case 'F':
      buttonStatus &= B111011;      // OFF
      Serial.println("\n** Button_3: OFF **");
      // your code...      
      displayStatus = "Motor #1 stopped";
      Serial.println(displayStatus);
      break;
// -----------------  BUTTON #4  -----------------------
    case 'G':
      buttonStatus |= B001000;       // ON
      Serial.println("\n** Button_4: ON **");
      // your code...      
      displayStatus = "Datafield update ";
      Serial.println(displayStatus);
      sendInterval = FAST;
      break;
    case 'H':
      buttonStatus &= B110111;    // OFF
      Serial.println("\n** Button_4: OFF **");
      // your code...      
      displayStatus = "Datafield update ";
      Serial.println(displayStatus);
      sendInterval = SLOW;
     break;
// -----------------  BUTTON #5  -----------------------
    case 'I':           // configured as momentary button
//      buttonStatus |= B010000;        // ON
      Serial.println("\n** Button_5: ++ pushed ++ **");
      // your code...      
      displayStatus = "Button5: 
";
      break;
//   case 'J':
//     buttonStatus &= B101111;        // OFF
//     // your code...      
//     break;
// -----------------  BUTTON #6  -----------------------
    case 'K':
      buttonStatus |= B100000;        // ON
      Serial.println("\n** Button_6: ON **");
      // your code...      
       displayStatus = "Button6 "; // Demo text message
     break;
    case 'L':
      buttonStatus &= B011111;        // OFF
      Serial.println("\n** Button_6: OFF **");
      // your code...      
      displayStatus = "Button6 ";
      break;
  }
// ---------------------------------------------------------------
}

Step 3: Bluetooth Module

HC05 is an apt bluetooth module but its range is any way not much greater

The Vcc and GND pin is connected to 5v and gnd of arduino
The Tx pin (transmitter)in of bluetooth should be connected to Rx(receiver) of arduino and Rx of bluetooth to Tx pin of arduino
No need to worry about other pins.
You can configure the Tx and Rx pin to your comfortability using SoftwareSerial library in arduino

#include<SoftwareSerial.h><softwareserial.h>

int Tx=3;
int Rx=4;
SoftwareSerial mySerial(Tx,Rx);

// so in this case the Tx of bluetooth connected to pin 4 and Rx to pin 3

Step 4: Configuring Bluetooth

You can put your bluetooth to AT command mode by putting the pin 34 of bluetooth to high

#include <softwareserial.h>
SoftwareSerial BTSerial(4, 3); //RX|| TX
void setup()
{
  pinMode(9, OUTPUT);  // this pin will pull the HC-05 pin 34 (key pin) HIGH to switch module to AT mode
  digitalWrite(9, HIGH);
  Serial.begin(9600);
  Serial.println("Enter AT commands:");
  BTSerial.begin(38400);  // HC-05 default speed in AT command more
}void loop()
{  // Keep reading from HC-05 and send to Arduino Serial Monitor
  if (BTSerial.available())
    Serial.write(BTSerial.read());  // Keep reading from Arduino Serial Monitor and send to HC-05
  if (Serial.available())
    BTSerial.write(Serial.read());
}

//upload the sketch

//Then open the serial port select baud rate to 9600 and select NL&CR mode

//Connect Tx and Rx of bluetooth pin to to 4,3 respectively  

// You can touch the pin 34 of bluetooth to pin 9 of arduino using a wire 

// disconnect the bluetooth while uploading the sketch as it will interrupt the uploading 

//now u can configure the baud rate of bluetooth ,give name to bluetooth ,set password to bluetooth....

//The file HC05 at command has codes to configure the bluetooth

//In order to check ur connection Enter AT in Serial port it will reply OK
//Enter  " AT+UART=57600,0,0  "  in serial port to change the baud rate of bluetooth