I recently had to make a design project for a class at school where the only requirement was the incorporation of a DE2 board. My partner and I originally wanted to construct a “frameless” laser harp (the Stephen Hobley variety), but due to budget, time, and logistical constraints, we opted for the slightly less ambitious route. The final product only utilized 2 laser pointers, some basic building materials, and the required board, and it turned out great.

Here is a little video of the harp in action with a quick explanation http://www.eecg.toronto.edu/~janders/241…

Project Steps

Getting materials. You will need:

Wood (1 2×4, 1 2×2)

Glass (10 pieces of 2.5″x2.5″)

Mirrors (4 pieces of 2.5″x2.5″)


Laser pointers (x2)

Resistors (12 2kohm, 12 photoresistors)

Wiremold (something like this http://www.homedepot.com/buy/electrical/…)

You want to first make the frame of the harp. Start by cutting the 2×4 into 4 pieces. 2 pieces at 3ft and 2 pieces at 2.75ft. These four pieces will then need to be assembled correctly by drilling them in place. You will also need to drill two hole along the top for the wiring, which will come a bit later. Take a look at the following schematic for a bit more detail.

To save a little bit of money and only buy 2 laser pointers, the glass and mirrors are used to split the laser beam 12 times. I will explain how this works in a bit more detail so it makes sense.

The two laser beams will be mounted on the either side of the frame pointing downwards. The beam will travel down and hit a mirror placed at exactly 135°. This will reflect the beam horizontally. The beam will then hit the pieces of glass. There will be 5 pieces of glass placed at 45°. They should be spaced out a bit (~2”). The pieces of glass will reflect a fraction of the light upwards while letting the majority of the light through.

I estimate that it is roughly 6-9% of the beam that actually gets reflected. After the beam travels through the 5 pieces of glass it should hit a mirror placed at 45°. This reflects whatever is left of the beam upwards. This should be repeated for the other laser pointer mounted on the other side of the frame. See the following images and the final results for clarification.

The next step has to deal with the glass and mirror holder. Basically you will have to slot the 2×2 to hold the pieces of glass. The margin of error here is very small, so measure 4 times if need be.

First cut the 2×2 so it fits across the inside of the frame. You should then measure out where the pieces of glass go. This should be around 2”. Take care when measuring out the space for the two mirrors in the centre. If you fail to give enough clearance for the mirrors that form a 90° with each other then you will have to start over, or cut the mirrors smaller (I speak from experience with this tip). Take a look at the diagram for clarification. After you measure twice, it is time to cut the slots. Make sure the slots are not too deep, but not too shallow either. I cut mine 1″ deep.

After you get that all cut up, screw/glue the 2×2 across the bottom of the frame. Mount the lasers on the sides of the frame. Cut the wiremold so that it fits across the inside of the frame. Mount it on the top of the frame (on the same side with the two holes that were drilled earlier). Place all the glass an mirrors in the correct slots and turn on the lasers. Mark on the wiremold where the lasers hit. Drill holes here. This is where the photoresisters will go, so make sure the holes are more or less the same size.

Next comes the wiring. The corresponding circuit diagram is shown below. We sent all the data to the DE2 using the expansion header. It is not a very complex circuit, but it gets the job done. We ended up using a 3.3V source since the intended 5V source was too high that there was not enough drop across the photoresistors.

The diagram only illustrates 3 notes, but you need 12 of these.

After everything is in place here comes the code. I cannot provide all the code that we wrote, but I can say the example Verilog code that comes with the board can be easily modified for this project.

Check out some of the final images