I am using LASER and LDR for this purpose. From the transmitter, I will send low frequency pulses using LASER to the receiver. The LDR on receiver side will receive these pulses in form of LASER light. It will trigger monostable multi-vibrator to regenerate same pulses. These pulses will further drive the stepper motor through driver circuit. So as anyone changes pulse frequency from transmitter, the stepper motor speed will change accordingly
This simple circuit can be used as an automatic bathroom lamp controller. It disables the bathroom lamp at daytime and enables it at night. The circuit is built around a light-dependant resistor (LDR1), reed switch (S1), two transistors BC547 (T1) and SK100 (T2), a 12V 1-change over (C/O) relay (RL1), a step-down transformer X1 (12V-0-12V, …
A simple sensitive intruder alarm circuit diagram and schematic using NE 555 IC, 741 IC as comparator and an LDR.This is a good thief/theft alarm circuit for home.
http://www.newark.com/photo-light-dependent-resistors-ldr Light Dependent Resistors work like in your car sensing the sun. When it gets dark the resistors ohmic value goes up and triggers the light circuit to come on.