Laser Tripwire Transmitter

Project 15 out of 18

Create a device that can sense if an item has passed through a laser pointer.

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Make the Security Center you’ve been building over the last few projects more advanced by adding another level. Use a laser diode that will combine with a light-dependent resistor to detect if someone walks through the laser beam. This information will get sent to the Wireless Control Center that you built in the last project. First, you’ll build a new wireless node with a laser beam and an LDR. To create the Laser Tripwire, you’ll use the laser diode to shine a beam into a mirror, which will direct the laser beam back to the LDR. If the laser beam is broken, the LDR will detect it. You’ll reprogram the Wireless Control Center to receive signals from both transmitters with the same radio. Then, build the Laser Tripwire Transmitter and program it to make it work. Now you have a fully operational Security System that can detect intruders in different ways.

Milestones Unlocked



Programming (C++)

Laser Diodes

Course Progression

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Finish your Laser Tripwire Transmitter project kit by completing the following exercises to solidify your understanding of laser diodes.

  • Make the LCD screen show the amount of time that’s passed since the alarm last went off.
  • Modify the code of the Control Center to sound the alarm only if laser beam and PIR sensors send an alert.
  • Make three different alarm patterns so that each different part of your Security Center has a different alarm sound.
  • Add a second mirror to your setup to form a triangular boundary.

Electronics Course


18 Projects


Ages 12+


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