Using a Shadow to Create a Light Seeking Sensor

Light Seeking System

Two photo resistors are positioned on opposite sides of a rectangular beam. It the beam is pointing at a light source both photoresistors produce equal values. If not aligned this balance is upset by the shadow of the beam and the difference in photo resistor output is used to rotate the beam using a stepper motor.

Gnd-- 10k--AnalogInPin--Photoresistor--3.3V

The code

//SeekSun1.js
// 7 Mar 2017
// add stepper motor code

// 4 Mar 2018
// Uses 2 photoresistors and 10k resistors to provide
// two analog inputs
// the LED color changes depending on the sign of the
// difference between the analog inputs.
//
//          |
//   pr1----|====pr2
// the vertical bar casts a shadow on the pr
// this creates a difference in input values
// use this to rotate the assembly so that the 
// difference in inputs is within the band
// Stepper Motor Interface Configuration
var action=0;
var Step=A8;//LED1;//A8;
var Dir=B7;
var pp=new Uint8Array(32);  // 16 microsteps *2,  see BigEasy docs
// Photo resistor Configuration
var P1=B1;
var P2=A7;

pp.fill(1); //pulse time in ms
pinMode(Step,"output");
pinMode(Dir,"output");
digitalWrite(Step,0);
digitalWrite(Dir,0^action);
clearInterval();

function move(d){
 digitalWrite(Dir,d^action);
 digitalPulse(Step,0,pp);
}

var verbose=1;//0;//1;
function clog(a){
  if(verbose>0)console.log(a);
}

var band=0.01;

pinMode(P1,'analog');
pinMode(P2,'analog');

clog(analogRead(P1));
clog(analogRead(P2));
var a,b,c,d;
var sss="";

setInterval(function(){
 a=analogRead(P1);
 b=analogRead(P2);
 sss=a.toString()+",";
 sss+=b.toString()+",";
 sss+=(a-b).toString();
 clog(sss);
 c=a-b;
 d=c;
 if(d<0)d=d*-1;
 if(d<band){
   digitalWrite(LED2,0);
   digitalWrite(LED1,0);
   //nomotion();
 }else{
  if(c<0){
   digitalWrite(LED1,0);
   digitalWrite(LED2,1);
   //rotleft();
   move(0);
 }
  if(c>0){
   digitalWrite(LED2,0);
   digitalWrite(LED1,1);
   //rotright();
   move(1);
  }
 }//end else
},1000);

Stepper Motor Stuff

Big Easy

or
BigEasy2

or for smaller stepper motors
EasyDriver

Wiring

Pico Bigeasy

Gnd Gnd

B7 Dir

A8 Step

Powered the BigEasy board with 12V

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