# Laser Maze Detection and Reflection

Mirrors were placed at a 45-degree angle from the laser beam. The laser reflects off the mirrors and travels in a square pattern back to the starting area to hit a photo resistor. Note: the target (where the photo resistor is located) and the laser source are not at the same height due to the difficulty of alignment when making the sketch model. Everything has to be very precise for good alignment! Note #2: the configuration of mirror I have shown here is simple for a more feasible sketch model. However, the intended configurations of the game will be more complicated. Refer to our storyboard.

## Question 1: How well will a laser reflect off mirrors?

I used the laser cutter to cut slits on a foam core base to place the mirrors in. I also cut slits to help me align the laser source and target clear acrylic pieces. The laser cutter was used to make the sketch model as precise as possible for better alignment. I glued acrylic to the mirrors to make sure they were straight. I learned that it is reasonable to reflect laser beams with mirrors but perfect alignment is difficult.

The idea for this sketch was to make a smaller and feasible version of the game to prove the concept. I did some research to make sure the concept does not fail when the game is made bigger, and the laser beam has to travel longer distances and be reflected off more mirrors.

The following calculations and assumptions are according to this Forbes article (link). The average mirror in a bathroom reflects about 90% of the visible light that hits it. The luminance of a 5 mW laser, which is the average power of a class IIIA (considered safe by the FDA (link)) hand-held presentation laser pointer has a luminance of 5X10^12 candela/squared meter. In our life-sized game we don't intend to use more than 8 mirrors to reflect the laser.

The math showing the luminance left after 8 reflections is as follows: (5X10^12) *0.90^8=2.15X10^12 candela/squared meter

For a Class II (1 mW) laser the math after 8 reflections is as follows: (1X10^12) *0.90^8=4.30X10^12 candela/squared meter

The human eye switches to night vision at about 0.001 candela/squared meter so my proof of concept still stands for a life-sized version of our game.

## Question 2: Can we sense when the laser has hit the target?

To answer this question, I used an Arduino with an LED and photo resistor. If the sensor senses the laser, the LED turns on as shown in the picture above. I learned that using a photo resistor to sense whether the laser has been correctly reflected to hit the target can be done.

Some problems with this: The laser may be hard to see without haze. However, because the open world rooms don't have a ceiling, keeping haze inside the game room might be a challenge. This requires some testing that we did not have the time to do for this deliverable. I found a Class II laser that is easy to see without haze (see below). We could use this kind of laser to avoid the haze problem.

The photo resistor is small so in order to get the correct alignment of the laser and sensor, the mirror pieces, and their alignment in relationship to the laser source and target has to be very precise. Even if the game was constructed and aligned perfectly, misalignments due to the deteriorating of mechanical parts (I am mainly talking about the mirrors pieces) might happen. We could use a lot of small sensors to allow space for error in alignment but this would not be practical. Another alternative is using a giant photo resistor but I could not find one online. Lastly, another alternative is to use a camera from a point above the game to see when the laser has hit the target. (Note: this would not work if the laser is not visible.)

## Safety

The laser I used is a Class II laser which is below the recommended Class IIIA (max power of 5 mW) as per the FDA (link).

The plan is also to place the laser at a point below the eye level of the average female while not causing users to bend over too much to the point where it would be uncomfortable.