I have always loved RC cars, but sadly I got to buy one when I was no more a kid. Recently I published an app to control any Bluetooth enabled car or robot. So why not to make a Bluetooth car to test it! Here I’m sharing step by step guide you can follow to make your own bluetooth controlled car with speed control.
To complete this project, you should have some basic electronics knowledge. If you have never worked on Arduino then first make a hello world project with Arduino to learn the basics.
Required Hardware
- L298 Dual H-bridge IC
- 2 x 0.5 ohm 2W resistors
- Arduino Uno, Nano or any other version with at least 2 pwm channels.
- HC-05 Bluetooth module
- 7.2V LiPo/Li-Ion battery (I used two mobile phone batteries connected in series)
- Veroboard and soldering equipment
- 2 x Tyre + motor
- 1 x Caster wheel
- Car chasis
If you want, you can skip the first two parts in the list and buy prebuilt Motor Driver Shield instead. It will save you from soldering.
Required Software
Step 1: Create the Motor Driver Circuit
Skip this step in case you choose to buy prebuilt Motor Driver Shield
H-Bridge is a circuit used to drive the motor in both directions. L298 makes H-Bridge circuit very simple. Here is the schematic diagram given for the circuit.
Step 2: Program Arduino
We will use BlueDuino app to control our car via Bluetooth. This app works on any windows 10 device. If you wanna control it using android phone, you might need to tweak the Arduino code a bit. Download the code (.ino file) and then upload it to Arduino. Make sure nothing is connected with the Rx pin of Arduino before you upload your code, otherwise upload will fail.
Reading a Chunk from Bluetooth
String ReadLine()
{
String s;
char c;
while (1)
{
if (Serial.available())
{
c = Serial.read();
if (c == '*')
{
continue;
}
else if (c == '#')
{
return s;
}
else
{
s += c;
}
}
}
}This function will return a string in a format like this: X,Y , where X and Y are single byte ASCII values of x-axis and y-axis of the joystick.
Getting Joystick Position
The app sends data in a format like this *X,Y# . Every command starts with * and ends with #. The app sends this string whenever the joystick is moved. Here X and Y are unsigned char. It’s value can vary from 0-255. When the joystick is in mid then x-axis = 127, y-axis = 127. On serial monitor a command might look like this *a,<#
void UpdateAxis(int *x, int *y, String chunk)
{
String s1, s2;
bool comma;
if (s.length() != 3) return;
*x = (int)(byte)s[0] - 127;
*y = (int)(byte)s[2] - 127;
}x and y are stored as global variables in the Arduino code.
Translating Axis Values to Motor Speeds
Now we need to convert x-axis , y-axis values to drive motors using differential drive. When joystick is at extreme forward i.e. x-axis = 255, y-axis = 127, then both motors should have maximum speed in the forward direction.
void ToDifferentialDrive(int xValue, int yValue)
{
if (yValue > 0)
{
if (xValue < 0)
{
left = mag + (HANDLING * xValue);
right = mag;
}
else
{
left = mag;
right = mag - (HANDLING * xValue);
}
}
else
{
if (xValue < 0)
{
left = -mag;
right = -mag - xValue;
}
else
{
left = -mag + xValue;
right = -mag;
}
}
}This function translates the x-axis and y-axis values into left and right motor speeds and updates the respective global variables. HANDLING is a constant that can be anywhere between 0-1. For me 0.6 is a suitable value.
Driving Motors
Now finally we will use those speed values to drive the motors.
void DriveMotor(int motor, int spd, int maxSpeed)
{
spd = 255 * ((double)spd / maxSpeed);
Serial.print(spd);
Serial.print(" === \t");
if (spd > 0)
{
analogWrite(motorPins[motor][0], spd);
digitalWrite(motorPins[motor][1], LOW);
}
else
{
analogWrite(motorPins[motor][0], (255 + spd));
digitalWrite(motorPins[motor][1], HIGH);
}
}maxSpeed determines the peak value of the left and right variables, which is 128. Increasing this value doesn’t increase the speed, so don’t change it!
Step 3: Connect the Circuit
- Connect the Arduino and motor driver circuit as follows
Arduino Motor Driver
pin 5 ———- pin 1
pin 6 ———- pin 2
pin 9 ———- pin 3
pin 10 ——– pin 4
5V ———— pin 5
GND——— pin 6
- Now connect motors with H-Bridge:
Motor Driver Motor
Out 1 ————— Motor 1 pin 1
Out 2 —————- Motor 1 pin 2
Out 3 —————- Motor 2 pin 1
Out 4 —————- Motor 2 pin 2
- OR If you are using Motor Driver Shield:
Arduino Motor Driver Shield
pin 5 ———- Input 1
pin 6 ———- Input 2
pin 9 ———- Input 3
pin 10 ——– Input 4
5V ———— 5V
GND——— GND
Also connect battery +ve to the terminal specified in the picture above and battery -ve to GND.
In case the motor turns opposite, swap the motor terminals for the respective motor.
- Connect the Bluetooth module (HC-05/HC-06) to Arduino as:
Arduino Bluetooth Module
Tx —————- Rx
Rx —————- Tx
3.3V ————- Vcc
GND ———— GND
Now you can power the Arduino directly through the battery using the power jack. On power jack, Arduino can bear upto 20V but the recommended voltage is 7-12V.
Step 4: Assemble the Car
Now we have everything ready, let’s assemble our car. My car is ugly as I don’t like to spend my time on decorating it but of course you can break convention of the geeks and make it beautiful.
Step 5: Start Driving!
After you download BlueDuino app from windows store. If you want to control the car using an Android or iPhone then you might need to tweak the code a bit according to the app you are using.
- Pair your phone to your HC-05 and connect using mobile phone settings. Default pairing code is 1234.
- Open the app and connect to your HC-05 from app.
- Go to joystick tab in the app and control your car using joystick!
If you experience problem in step one then make sure your device supports Bluetooth Smart Ready not Bluetooth Smart (BLE) and also check if Bluetooth is turned on. If your device is Bluetooth Smart then you require BLE module which is currently not supported by the app.
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