In this instructable I will show you how to make a laser spirograph that changes forms automatically, and without the need to program an Audrino. This is accomplish by the use of 3 almost identical circuits that controls the 3 electric motors.
Step 1: How It Works
As you can see in the picture there is one circuit board with the tree individual circuits, three motors (two computer fans and a normal motor) with mirrors attached, and a green laser pointer. I use a laser that has a switch instead of a button, so I can leave it on while I enjoy the show.
Like I already pointed out, in each motor there is a circular mirror. These mirrors are from disposable dental mirrors, because they are already rounded, have a nice size and are easy to work with. The mirrors are glued in a coaxial way with the motor, but they have a small tilt. When the laser strikes the spinning surface of the tilt mirror, it is reflected forming a circle. If this circle is projected into another spinning tilt mirror it will form a variety of shapes, depending on the motors velocity and other factors. Adding a third motor just opens the possibility to even more complex shapes.
If you want to see it in a more scientific way, the resulting shape is the plot on polar coordinates of the following equation: f(r,ø) = A sen (x* ø) + B sen (y* ø) + C sen (z* ø). Were “A”, “B” and “C” are the amplitude that is the mean of how much the mirror is tilt, and “x”, “y” and “z” are the velocity of each motor and the offset between them.
So to be able to change the shape that is plotted you need to change the amplitude, the offset or the velocity. I can’t think of a simple way to change the amplitude, you couldn’t control the offset unless you used stepped motors and that is out of my reach. So what I did was to change the velocity of each motor.
Step 2: The Circuit
Each motor velocity is controlled by an individual circuit using Pulse Width Modulation. You might ask me why I used PWM, and I will tell you that I choose to use PWM because in an early stage of the design I was controlling the motors with variable resistances, and I couldn’t reach the range of velocities I was hopping because the motors stop working in an early point. When you use PWM you can make every pulse as apart as you want and the motor wouldn’t mind because you are given it a boost of power, so you can make it go as slow as you want. (I don’t know if I make myself clear, if not you can ask me in a comment).
I used a simple timing circuit to make the PWM using the famous NE555. But this circuit would always deliver the same pulse every time, and I wanted to be able to change shapes on their own. So I decided to feed the timing circuit with a triangular wave that will change the settings of the PWM. To generate this wave I used a Dual JFET operational amp. And to make it even better, the triangular wave for every motor circuit is different. This is accomplishing by changing the capacitor in the circuit (C1).
Step 3: More About the Circuit
The values for each component I used are as follow:
R1: 270 kΩ
R2: 220 kΩ
R3: 100 kΩ
R4 = R5: 300 Ω
C1: 47 μF, 100 μF, 150 μF
C2: 3.3 μF
If you have work with the NE555, you will notice that the values I used are pretty low; this is because I wanted a short pulse that can be trigger very close together or far apart. Also if you see in detail both diagrams, you will notice that I used different voltages for each part of the circuit. This is because I couldn’t find any other way to make it work. For the power supply I used an old computer power source (I used +12V, -12V, +5V, -5V and Ground).
The motors are connected to each NE555 output (Pin #3) and ground.
Step 4: Final Thoughts
If you see in the pictures, the laser strikes the first mirror in a 45° angle, so the reflection will exit also in a 45° angle in to the next mirror and so on. You don’t want to attach the motors to the case in a very permanent way until you have tried it out, because the angles may be a little off and you will have to fix the positions of the motors.
And finally I added a screw in the front so I could easily change the whole thing tilt like a projector.
Thanks for your attention. Hope you enjoyed this Instructable, I know I did. :D
P.D: Sorry about the low resolution video, but it was the only way I found to show the true nature of this laser show. In higher quality it looked weird, maybe something about the fps and the way this works...