Patrick Müller
Published © GPL3+

Take Control Over Lego Power Functions

Learn how to control Lego motors and servos with your Arduino and build your own Android app to remote control your model.

BeginnerFull instructions provided5 hours54,532
Take Control Over Lego Power Functions

Things used in this project

Hardware components

Arduino UNO & Genuino UNO
Arduino UNO & Genuino UNO
×1
Dual H-Bridge motor drivers L293D
Texas Instruments Dual H-Bridge motor drivers L293D
(buy one with long pins, not the surface-mount version shown on the photo)
×1
Breadboard (generic)
Breadboard (generic)
×1
9V to Barrel Jack Connector
9V to Barrel Jack Connector
×1
Lego Power Functions Extension wire (Item: 8886)
×3
HC-05 Bluetooth Module
HC-05 Bluetooth Module
×1

Story

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Schematics

Github Lego-car-Arduino

Contains source code Arduino; Fritzing diagram; source code android app for upload to MIT app inventor

Fritzing diagram breadboard Lego-car-Arduino

Fritzing diagram Lego car

Fritzing diagram schematics Lego-car-Arduino

Code

Legocar_v3_bluetooth

Arduino
/*
 Lego Powerfunctions car model controlled over bluetooth
 Arduino Uno controls motors and servo
 Remote controlled with android app developed with MIT App Inventor 2
 
 Circuit:
 * Serial communication   (uses Uno pin 0,1)    Bluetooth-module is attached (has to be detached when loading program over USB)
 * L293D with motor       (uses Uno digital pins 2,5,9)
 * L293D with servo       (uses Uno digital pins 6,8,3)
 
 
*/

// Used libraries:
#include <SPI.h>                             // Serial Peripheral Interface Library
#include <String.h>                          // contains function strtok: split string into tokens


// Serial buffer size: calculate based on max input size expected for one command over bluetooth serial interface
#define INPUT_SIZE 30

// Motor control digital output pins defined as global constants (4 wheel drive with 2 Lego motors):
const int controlPin1A = 2;                  // L293D driver input 1A on pin no 2  http://www.ti.com/lit/ds/symlink/l293.pdf connected to Arduino digital output pin 2
const int controlPin2A = 5;                  // L293D driver input 2A on pin no 7 connected to Arduino digital output pin 5
const int ENablePin = 9;                     // L293D ENable(1,2) input on pin no 1 connected to Arduino digital output pin 9
// Servo control digital output pins defined as global constants (Servo steering with 1 Lego servo):
const int controlPin3A = 6;                  // L293D driver input 3A on pin no 10 connected to Arduino digital output pin 6
const int controlPin4A = 8;                  // L293D driver input 4A on pin no 15 connected to Arduino digital output pin 8 
const int servoENablePin = 3;                // L293D ENable(3,4) input on pin no 9 connected to Arduino digital output pin 3
// Motor control global variables: 
int motorSpeed = 0;                          // Motor speed 0..255
int motorDirection = 1;                      // Forward (1) or reverse (0)
// Servo control global variables:
int steering = 0;                            // Servo position 0..255
int steeringDirection = 0;                   // Left (0) and Right (1)



void setup() 
{
   Serial.begin(9600);                       // initialize serial communication
   Serial.setTimeout(1000);                  // 1000 ms time out
   // Declare digital output pins:
   pinMode(controlPin1A, OUTPUT);      // 1A
   pinMode(controlPin2A, OUTPUT);      // 2A
   pinMode(ENablePin, OUTPUT);         // EN1,2
   pinMode(controlPin3A, OUTPUT);      // 3A
   pinMode(controlPin4A, OUTPUT);      // 4A
   pinMode(servoENablePin, OUTPUT);    // EN3,4
   digitalWrite(ENablePin, LOW);       // motor off
   digitalWrite(servoENablePin, LOW);  // steering centered
}


void loop() 
{
   // Get next command from serial bluetooth (add 1 byte for final 0)
   char input[INPUT_SIZE + 1];                  // array of type char (C-string) with null-termination (https://www.arduino.cc/en/Reference/String)
   byte size = Serial.readBytesUntil('\n', input, INPUT_SIZE);   //read Serial until new line or buffer full or time out
   // Add the final 0 to end the C-string
   input[size] = 0;

   // Read command which is a C-string of the form:  "RC,RCsteering,RCspeed,\n\0"  (ends with a new line character and a null)
   char* command = strtok(input, ",");          // ignore command for now (RC for Remote Control is the only command sent by the app for the time being)    
   char* RCsteering = strtok(NULL, ",");        // next comes RCsteering which is in the Range: -100 (left).. 0 .. 100 (right)
   char* RCspeed = strtok(NULL, ",");           // next comes RCspeed which is in the Range: -100 (full speed reverse).. 0 .. 100 (full speed forward)
   int iRCsteering = atoi(RCsteering);          // convert string RCsteering into integer iRCsteering
   int iRCspeed = atoi(RCspeed);                // convert string RCspeed into integer iRCspeed
   
   // Set motor and servo control variables
   if (iRCsteering > 0) steeringDirection = 1;   // turn right if iRCsteering = 1..100
   else steeringDirection = 0;                   // turn left  if iRCsteering = -100..0
   steering = int(2.55*abs(iRCsteering));        // Servo position 0..255 based on command 0..100
   if (iRCspeed > 0) motorDirection = 1;         // Set car in forward if iRCspeed = 1..100
   else motorDirection = 0;                      // Set car in reverse if iRCspeed = -100..0
   motorSpeed = int(2.55*abs(iRCspeed));         // Set speed 0..255 based on command 0..100
   
   SetMotorControl();                            // adjust motor direction and speed 
}




void SetMotorControl()
/*
L293 logic:    EN1,2   1A    2A
               H       H     L    Motor turns left  (Forward; motorDirection == 1)
               H       L     H    Motor turns right (Reverse; motorDirection == 0)
               
               EN3,4   3A    4A
               H       H     L    Servo turns left  (steeringDirection == 0)
               H       L     H    Servo turns right (steeringDirection == 1)

Motor speed:   PWM signal on EN1,2 (490 Hz; digital output value 0..255 for motorSpeed)
Servo position:PWM signal on EN3,4 (490 Hz; digital output value 0..255 for position; 0 is straight ahead)
*/
{
  if (motorDirection == 1)               //Forward
    {
       digitalWrite(controlPin1A, HIGH);
       digitalWrite(controlPin2A, LOW);
    }
  else                                   //Reverse
    {
       digitalWrite(controlPin1A, LOW);
       digitalWrite(controlPin2A, HIGH);
    } 
  analogWrite(ENablePin, motorSpeed);    //Speed
    
  if (steeringDirection == 0)            //Left
    {
       digitalWrite(controlPin3A, HIGH);
       digitalWrite(controlPin4A, LOW);
    }
  else                                   //Right
    {
       digitalWrite(controlPin3A, LOW);
       digitalWrite(controlPin4A, HIGH);
    } 
  analogWrite(servoENablePin, steering); //Servo position

}

Github Lego-car-Arduino

Contains source code Arduino; Fritzing diagram; source code android app for uploading to MIT app inventor

Credits

Patrick Müller

Patrick Müller

2 projects • 25 followers
Hobbyist, mechanical engineer and father of curious children

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