How to Build a Laser Tripwire

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  1. Connect the one end of the relay coil to the collector of the transistor.
  2. Connect the other end of the coil to +V end of the power source.
  3. Connect your resistor and LDR to the base of the transistor.
  4. Connect the resistor to +V and the LDR to ground.
  5. Connect the emitter to ground.
  6. ????
  7. PROFIT!!!!