Monday, 13 June 2011

Arduino and Matlab

I wanted to use Matlab's optimisation tool to optimise the sweep timings of the infra red sensor. To do this required the Arduino and Matlab have to communicate. Now Matlab has a toolbox for this, but I wanted my Arduino code as unchanged as possible and to run as fast as it would in normal operating conditions. So I decided to get Matlab to only talk to the Arduino via the USB cable, not program it. The Matlab code I used is this

function y=scan_results(x)

try
 
    dt_servo=x(1);
    dt_ir=x(2);
    n=x(3);
    resolution=20;
 
    %open serial port
    s = serial('COM4','BaudRate',115200);
    set(s,'DataBits', 8);
    set(s,'StopBits', 1);
    set(s,'Timeout', 60);
    fopen(s);
 
    %Read a line of data
    line=fgetl(s);
    fprintf('%s\n',line);
 
    %send the dt_servo value
    fwrite(s,int8(dt_servo));
     
    %Read a line of data
    line=fgetl(s);
    fprintf('%s\n',line);
 
    %send the dt_ir value
    fwrite(s,int8(dt_ir));
    
    %Read a line of data
    line=fgetl(s);
    fprintf('%s\n',line);
 
    %send the n value
    fwrite(s,int8(n));
     
    %Read a line of data
    line=fgetl(s);
    fprintf('%s\n',line);
     
    %Read a line of data
    line=fgetl(s);
    fprintf('%s\n',line);
 
    %Read data from Arduino
    angle=zeros(3,resolution+1);
    old_map=zeros(3,resolution+1);
    new_map=zeros(3,resolution+1);
    scan_right=zeros(3,resolution+1);
    scan_left=zeros(3,resolution+1);
    for i=1:3
        %Read angle data
        %Read a line of data
        line=fgetl(s);
%         fprintf('%s\n',line);
 
        %Read a line of data
        line=fgetl(s);
%         fprintf('%s\n',line);
        angle(i,:)=str2num(line);
     
        
        %Read old_map data
        %Read a line of data
        line=fgetl(s);
%         fprintf('%s\n',line);
     
        %Read a line of data
        line=fgetl(s);
%         fprintf('%s\n',line);
        old_map(i,:)=str2num(line);  
     
     
        %Read new_map data
        %Read a line of data
        line=fgetl(s);
%         fprintf('%s\n',line);
     
        %Read a line of data
        line=fgetl(s);
%         fprintf('%s\n',line);
        new_map(i,:)=str2num(line);
 
     
        %Read scan_right data
        %Read a line of data
        line=fgetl(s);
%         fprintf('%s\n',line);
     
        %Read a line of data
        line=fgetl(s);
%         fprintf('%s\n',line);
        scan_right(i,:)=str2num(line);
 
     
        %Read scan_left data
        %Read a line of data
        line=fgetl(s);
%         fprintf('%s\n',line);
     
        %Read a line of data
        line=fgetl(s);
%         fprintf('%s\n',line);
        scan_left(i,:)=str2num(line);
     
%         figure(i)
%         polar((angle(i,:)/180)*pi,scan_right(i,:),'b')
%         hold on
%         polar((angle(i,:)/180)*pi,scan_left(i,:),'r')
%         hold off      
 
        y=0;
        for j=1:resolution+1
            y=y+sqrt((scan_right(i,j)-scan_left(i,j))^2); %objective function
        end
     
    end
 
 
    y=y+(dt_servo+dt_ir+n)*1; %objective function

catch
 
    %close serial port
    fclose(s);
    delete(s);
    clear s;

end

try
%close serial port
fclose(s);
delete(s);
clear s;

catch
 
end

fprintf('Results Obtained\n\n');

This function that opens a serial port to the Arduino with the same baud rate as the Serial.begin command on the Arduino. The databits and stopbits also need to be defined for it to work. It all needs to be in a try catch mechanism, so that the serial port is always closed. If the port isn't closed then you have to exit Matlab and reopen it. It was written to allow a Matlab optimiser to call it and it returns the value of my objective function. The rest of the program makes more sense when you can see what the Arduino code is doing.

#include <Servo.h>

#define resolution 20     //larger number means more accurate, but also more ram used
#define totalangle 100    //total angle that it turns 

#define scannercentre 79  //the scanner servo centre location
#define scannermin 3      //the pwm value to give an angle of 0 degrees
#define scannermax 152    //the pwm value to give an angle of 180 degrees

//define servos
Servo scanner;            // create servo object to control the sweeping servo 

//variables
int res2=resolution*0.5;
boolean initial=true;
int i,j,k;
int dt_servo=10000;           //delay for scanner servo to move to position in ms
int dt_ir=47;              //delay for the ir sensor to refresh in ms
int n=10;                  //number of readings to average from ir sensor
int reading;       // used for taking the averages
float dist;        // used for calculating the distance in cm

int new_map[resolution+offset+1]; //store the distances from the ir sensor
int old_map[resolution+offset+1]; //store the distances from the ir sensor
int scan_left[resolution+offset+1]; //store the distances from the ir sensor
int scan_right[resolution+offset+1]; //store the distances from the ir sensor
int angle[resolution+1];      //stores the angles at which data was taken

boolean run=false;

void setup()
{
  scanner.attach(6);    // attaches the servo on pin 6 to the servo object 

  Serial.begin(115200); // sets the speed of the serial connection to the computer

  scanner.write(scannercentre);    // sets the scanner servo to the centre

  analogReference(EXTERNAL);  // Set the ADC reference voltage to external (only use if using 3V, read this first)

  //calculate the angles to be used
  for(i=0;i<res2;i++) { //right sweep
    angle[i]=90-((res2-i)*(totalangle/resolution));
  }
  angle[res2]=90;  //centre
  for(i=res2+1;i<resolution+1;i++) { //left sweep
    angle[i]=90+((i-res2)*(totalangle/resolution));
  }

  //for debugging...
//  for(i=0;i<resolution+1;i++) {
//    Serial.print(i);
//    Serial.print(" ");
//    Serial.println(angle[i]);
//  }

  pinMode(13,OUTPUT);

  digitalWrite(13,HIGH);
  delay(1000);
  digitalWrite(13,LOW);
  delay(1000);

}

// This runs continuously on the arduino
void loop() {

  if(run==false) {
    Serial.println("Waiting for inputs");
    dt_servo=Serial.read();
    while(dt_servo==-1) {
      dt_servo=Serial.read();
      delay(100);
    }
    Serial.print("dt_servo = ");
    Serial.println(dt_servo);
 
    dt_ir=Serial.read();
    while(dt_ir==-1) {
      dt_ir=Serial.read();
      delay(100);
    }
    Serial.print("dt_ir = ");
    Serial.println(dt_ir);
 
    n=Serial.read();
    while(n==-1) {
      n=Serial.read();
      delay(100);
    }
    Serial.print("n = ");
    Serial.println(n);
 
    Serial.println("Done Reading");
    digitalWrite(13,HIGH);
    run=true;
  }
  else {
    for(k=0;k<3;k++) {
      for(i=0;i<(resolution*2)+2;i++) {
     
        //Look
        look();     
      }
   
      //print maps
      Serial.println("Angle:");
      for(i=0;i<resolution+1;i++) {
        Serial.print(angle[i]);
        if(i!=resolution) {
          Serial.print(" ");
        }
        else {
          Serial.println(" ");
        }
      }
      Serial.println("Old Map:");
      for(i=0;i<resolution+1;i++) {
        Serial.print(old_map[i]);
        if(i!=resolution) {
          Serial.print(" ");
        }
        else {
          Serial.println(" ");
        }
      }
      Serial.println("New Map:");
      for(i=0;i<resolution+1;i++) {
        Serial.print(new_map[i]);
        if(i!=resolution) {
          Serial.print(" ");
        }
        else {
          Serial.println(" ");
        }
      }
      Serial.println("Scan Right:");
      for(i=0;i<resolution+1;i++) {
        Serial.print(scan_right[i]);
        if(i!=resolution) {
          Serial.print(" ");
        }
        else {
          Serial.println(" ");
        }
      }
      Serial.println("Scan Left:");
      for(i=0;i<resolution+1;i++) {
        Serial.print(scan_left[i]);
        if(i!=resolution) {
          Serial.print(" ");
        }
        else {
          Serial.println(" ");
        }
      }
   
    }
    run=false;
    digitalWrite(13,LOW);
  }
}

void look() {

  if(i==0) { //read front
    //move servo to position
    scanner.write(mapscanner(angle[res2]));
    delay(dt_servo);
    take_reading();
    //update map
    old_map[res2]=new_map[res2]; //update old map
    new_map[res2]=(int)dist;
    scan_right[res2]=(int)dist;
  }
  else if(i>0 && i<res2+1) { //sweep right
    //move servo to position
    scanner.write(mapscanner(angle[res2-i]));
    delay(dt_servo);
    take_reading();
    //update map
    old_map[res2-i]=new_map[res2-i]; //update old map
    new_map[res2-i]=(int)dist;
    scan_right[res2-i]=(int)dist;
  }
  else if(i>res2 && i<resolution+1) { //sweep left to centre
    //move servo to position
    scanner.write(mapscanner(angle[i-res2-1]));
    delay(dt_servo);
    take_reading();
    //update map|
    new_map[i-res2-1]+=(int)dist;
    new_map[i-res2-1]*=0.5;
    scan_left[i-res2-1]=(int)dist;
  }
  else if(i==resolution+1) { //read front
    scanner.write(mapscanner(angle[res2]));
    delay(dt_servo);
    take_reading();
    //update map by averaging the two values
    new_map[res2]+=(int)dist;
    new_map[res2]*=0.5;
    scan_left[res2]=(int)dist;
  }
  else if(i>resolution+1 && i<resolution*1.5+2) { //sweep left
    //move servo to position
    scanner.write(mapscanner(angle[res2+1+i-resolution-2]));
    delay(dt_servo);
    take_reading();
    //update map
    old_map[res2+1+i-resolution-2]=new_map[res2+1+i-resolution-2]; //update old map
    new_map[res2+1+i-resolution-2]=(int)dist;
    scan_left[res2+1+i-resolution-2]=(int)dist;
  }
  else if(i>resolution*1.5+1 && i<resolution*2+2) { //sweep right to centre
    //move servo to position
    scanner.write(mapscanner(angle[resolution-(i-resolution-res2-2)]));
    delay(dt_servo);
    take_reading();
    //update map|
    new_map[resolution-(i-resolution-res2-2)]+=(int)dist;
    new_map[resolution-(i-resolution-res2-2)]*=0.5;
    scan_right[resolution-(i-resolution-res2-2)]=(int)dist;
  }

}

//map the desired angle to the value required to move the servo to that angle
int mapscanner(int angle) {
  //Serial.println(angle);  //for debugging the code
  float u=angle/180.0;
  //Serial.println(u);  //for debugging the code
  return(scannermin+(u*(scannermax-scannermin)));
}

//take readings from ir sensor
void take_reading() {

    delay(dt_ir); //wait for ir sensor to refresh

    reading=0;                // needs to start at 0 and then n readings will be added to it

    for(j=0;j<n;j++) {
      reading+=analogRead(0); // read from analog input 0
      delay(1);                          // wait one millisecond
    }
    reading/=n;           // finally average the n reading  
    dist=12214.16*pow(reading*0.5,-1.08);  // this calculates the distance 
    if(dist<10) {
      dist=0;
    }
    else if(dist>80) {
      dist=80;
    }
}

There aren't as many comments as usually, when I have a chance I will add some more. The code pretty much waits for 3 inputs from Matlab and then runs the sweep 3 times. Then it waits for another set of 3 parameters from Matlab and so on. It has an LED attached to pin13 to show when it is ready and when it is working. The sweep is different from my first attempts, it starts from the centre and goes right and then left and then right back to the centre.

At the end of the day the I couldn't get the optimiser to work as I desired. The optimiser fmincon doesn't allow integer parameters and the genetic algorithm is very slow and eventually cheated and converged to the minimum time I allowed. This was probably because the infra red sensor voltage changes every 32ms, so if it takes all the reading in this time it minimises the objective function... but doesn't give the optimised timings that I wanted.

I expect to edit this post when I have a chance (I have a PhD viva to prepare for) to clean it up and add more comment...

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