i get 7volt when led,hole,ldr come in line.otherwise it gives less than 7volts.it goes down to 2 volts and then in the next revolution when the led,hole(in gear) and ldr come in line,it again gives 7volts.the only problem is to change this varying output of ldr to a square waveform(either 0 or 1).i've studied that comparator does this job quite well.when the voltage goes beyond reference voltage,it gives 1 otherwise 0. so please help me with the circuit of comparataor.please help me with it.thanks