Fig. 1: The laser dance pad (front view).

Fig. 2: The laser pad (angle view).

The Laser Dance Matrix a.k.a The Laser Dancepad

History

The laser dancepad was first envisioned as a pulsed infrared device that did not involve any lasers. The theory behind the operation of the infrared dance pad was quite realistic and a prototype was fashioned. Unfortunately, there were significant discrepancies between the manufacturer's spec. sheets and the actual performance of their components, especially in regard to the infrared detection modules. Also, some of the modules had "features" that made them quite unusable for this device. Although, for the record, two out of the four buttons on the infrared pad were made to work quite well. Those modules turned out to be the exception rather than the standard.

Not to be put off by these difficulties, it was decided that a new detection method was needed for reliable operation. After finding a source of inexpensive laser diodes and constructing a test "button", a final prototype was built. While there were some construction issues, they were resolved satisfactorily. The first known laser-based dance pad became fully operational 5:48 PM PDT Wednesday 2007.04.25.

How It Works

Actually, the mechanics of the laser dance pad are simple (especially when compared with those of the pulsed infrared prototype). The control box holds four independent laser diode driving circuits as well as circuits for beam detection and USB interfacing.

Fig. 3: The control box interior.

The driver circuit provides constant current (and protection) to four 635nm red laser diodes.

Fig. 4: The laser diodes.

Detection is achieved using CdS (cadmium sulfide) photocells. Silicon phototransistors were implemented in a breadboard test, but did not have desirable characteristics. Also, they proved to be a very small target to hit with a laser from 1 meter away. The photocells did require an opaque shielding for immunity to daylight and ambient light. USB interfacing is provided by a Cypress chip taken from a Logitech Gamepad. There are also two momentary pushbuttons on top of the control box to function as 'Start' and 'Back'.

Gameplay is similar to any hard or soft dance pad with the notable exception that the playing surface is whatever lies beneath the laserpad. A button press is triggered when the player's foot (or other body part) interrupts the laser beam from shining upon the photocell.

Fig. 5: Illustrative diagram. (laser beams and lines added for clarity)

The beam is located very near to the floor so responsivity is excellent. The laserpad was designed specifically to function with the excellent DDR simulator 'Stepmania', but any dance game with USB input could work.

Notes

The full name "Laser Dance Matrix" arose from the fact that there is actually no "pad" or other playing surface included with the device. The matrix part is also somewhat accurate in reference to linear algebra.

The images of the laser dance pad were taken against a white background to highlight the structure of the device. More interesting images may be added later.

Contrary to popular belief, countless television programs and movies, laser beams cannot be seen from the side unless they are reflecting off of something like fog or dust. That is why the lasers are not visible in any images.

The laser dance matrix uses a 9-volt switching power supply, because USB cannot provide nearly enough power for all of the electronics on board.

It is helpful when playing to put some tape on the floor to find the center of the playing surface.

Using lasers instead of infrared LEDs make this project 23% more cool.

The entire project was completed without one reference to, or imitation of, Dr. Evil. (The previous reference excepted.)