motors needed

A fragment of the datasheet, of a now discontinued servo. And the wheels.

light sensors needed

The 650nm bandpass filters are 6mm x 6mm square. I glued them onto the photoresistors. I don't have specifications on the blue filters because I just cut them from the front panel of an old DVD player. The blue "eyes" filter out the red and respond otherwise to the ambient light (unless the ambient light is red). When the blue eyes detect brightness, the robot backs away. It's like the blue pill ... it's trying to go back to the way things were ... living in the dark unknown of artificial purpose. The red "eyes" are like the red pill ... and one could, if one were so inclined, make this robot follow the red light down into a rabbit hole.

collision sensors needed

power is needed

software is needed

Circuit Construction

SWL : Left side bumper/switch SWR : Right side bumper/switch RLA : Resistor, Left Ambient RRA : Resistor, Right Ambient RLE : Resistor, Left Eye RRE : Resistor, Right Eye A2,A3,A4,A5 : Arduino analog pins 2 - 5 D2,D3 : Arduino digital pins 2 and 3

The code: gathering sensor data

With a DVM I measured the photoresistor resistance in three conditions and got the following: 96KΩ with the room very dark. 700Ω with the room very bright. 1700Ω with the room normal, with the LASER light reflecting off a manila colored folder 1" away. From the circuit diagram, you can see it's a voltage divider with the photoresistors and a 10K fixed resistor. So that's 5v x 10K/(10K + RRxE) and that should provide a range of 0.47v to 4.27v: 5v x 10K/(10K + 96K) = 0.47 v 5v x 10K/(10K + 1.7K) = 4.27v So it's almost a factor of 10 from dark to bright.

const int RightAmbPin = A4; const int Left_AmbPin = A3; const int RightEyePin = A5; const int Left_EyePin = A2; int RightAmbVal = 0; int Left_AmbVal = 0; int RightEyeVal = 0; int Left_EyeVal = 0; void setup() { Serial.begin(9600); Serial.print("Left_AmbVal"); Serial.print(" "); Serial.print("Left_EyeVal"); Serial.print(" :: "); Serial.print("RightAmbVal"); Serial.print(" "); Serial.println("RightEyeVal"); } void loop() { RightEyeVal = analogRead(RightEyePin); Left_EyeVal = analogRead(Left_EyePin); RightAmbVal = analogRead(RightAmbPin); Left_AmbVal = analogRead(Left_AmbPin); Serial.print(Left_AmbVal); Serial.print(" "); Serial.print(Left_EyeVal); Serial.print(" :: "); Serial.print(RightAmbVal); Serial.print(" "); delay (500) ; } analogtestSerial.ino

But that's not what I measure in the real system. Because I'm not going to try to do this in darkness, or to film in the dark, it's the difference between normal lighting and the normal lighting with the LASER light that matters. And from the plot above, that's only about 1.4x: Right:Dark ―10x➝ Normal room light ―1.35x➝ LASER light close Left:  Dark ―4x➝ Normal room light ―1.4x➝ LASER light close

The code: robot control

1. BB: Bang-bang control
2. P: Proportional control
3. DPPMD: Decaying Proportional Poor-Man's Derivative control

void loop() 
{ 
  calibrating to find reference and peak values.
  ...
  calibration done
  ...
  // get the state of the outside world:
  RightEyeVal  = analogRead(RightEyePin);
  ...
     if (firsttimethrough == 1) 
     {
       // Proportional is a y = mx +b kind of thing:
       mR = float(90/(float(RightEyePeak) - float(RE_Ref))) ;
       bR = mR*RE_Ref ;
     }


#ifdef USE_DERIVATIVE
    reloadRight = (RightEyeVal > RightEyeComputedVal) ? 1 : 0 ; 
#else
    reloadRight = 0 ; 
#endif
    RightEyeComputedVal = 0 ;


#ifdef USE_ROLLINGAVERAGE
    for (i=0 ; i < (ArrayLength-1); i++) 
    {
      RightEyeComputedVal = RightEyeComputedVal + RightEyeArray[i] ;
      RightEyeArray[i]   = (reloadRight) ? RightEyeVal : RightEyeArray[i+1] ; 
    }
    RightEyeArray[ArrayLength-1] = RightEyeVal ;
    RightEyeComputedVal = float ((RightEyeComputedVal + RightEyeVal)/ArrayLength) ;
#else   
    RightEyeComputedVal = RightEyeVal;
#endif


      Left_Speed = int( (RightEyeComputedVal*mR) - bR) ;

      
#ifdef USE_BANG_BANG
      Rthresh = RE_Ref + 10 ;
      Lthresh = LE_Ref + 10 ;
      // Bang-bang control. Just go when the light is a wee bit above threshold.
      if ((RightEyeComputedVal > Rthresh) 
           && (Left_EyeComputedVal > Lthresh)){ Left_Speed =  90 ; }
      else if (RightEyeComputedVal > Rthresh) { Left_Speed =  90 ; }
      else if (Left_EyeComputedVal > Lthresh) { Left_Speed = -90 ; }
      else                                    { Left_Speed =   0 ; }
#endif


      // Finally convert the values to L and R servo sense.
      // Lspeed above 90 is forward motion.
      Left_Speed = 90 + Left_Speed ;
      Left_Servo.write(Left_Speed) ;
...
}

notes on the calculations

const int LE_RefDesignMin  =  100;
const int LE_RefDesignMax  =  250;
const int LE_PeakDesignMin =  300;
const int LE_PeakDesignMax = 1000;

const int RE_RefDesignMin  =  100;
const int RE_RefDesignMax  =  320;
const int RE_PeakDesignMin =  370;
const int RE_PeakDesignMax = 1000;

Results

Discussion and possibilities

Parts list