What You Should Know about Lasers for the Arduino
Laser trip wires are made up of two parts, a laser light source and a light sensor. With an Arduino, you can make a laser trip wire very simply and trigger anything you want from it. As you know from the movies, when the beam is broken an alarm sounds and the henchmen come running. You can build one yourself using a few simple components.
Complexity: Lasers are a difficult subject area because of the potential risks of working with them. But rather than risk your eyesight or spend a few years studying, why not use something that’s already been tested, certified, and turned into a product?
Laser pens or laser pointers are widely available and relatively cheap. These are usually Class 1 lasers, the lowest class, and are visible and safe under all conditions of normal use, but you’re still advised to check the specifications. Adults are normally sensible enough not to look directly into the laser, but with children, you want to err on the side of caution and find another sensor.
Because a laser beam is so precise, it’s best to choose one with a fairly large sensor so that you have a large area to aim for. The only added complexity of this sensor may be powering the laser. A laser pointer is usually battery powered, so you may need to replace the batteries every few days or wire a power supply of equal value to the battery compartment.
To make them useful in the outside world, you should house both the laser and the light sensor in enclosures. A nice touch is to mount the enclosures on mini tripods to give you some flexibility when aligning them.
Cost: For around $15 (£10) you can purchase a small, discreet laser pointer from RadioShack, in the United States, or Maplin in the United Kingdom. Battery life and beam color are the main differences between pointers. The light sensor costs around 75 cents to $2.50, depending on the size. If you opt for an enclosure, it may cost around $6 (£4). A mini tripod is around $9 (£6).
Where: If you have a fixed location for your tripwire, mounting the enclosure on either side of a doorway is simple. The best position is as low to the floor as possible to avoid eye contact with the laser. If you’re not sure where you want it or want to try a few ideas, keep it mobile and take your tripod-mounted trip wire with you wherever it’s needed.
The laser trip wire is a refinement of a conventional light sensor. By providing a more intense, controlled light source, you can increase the accuracy of a simple light sensor.