Introduction: Sound Activated Planetarium

This instructable was created in fulfillment of the project requirement of the Makecourse at the University of South Florida (

This is my sound activated planetarium. The basic function of the planetarium is to activate with the presence of a loud sound, such as a clap, and recreate the orbit of the moon and Earth around the sun. This is a fun and simple project that can be easily recreated and will make a nice decorative and interactive piece to display.

In this Instructable, I will explain how to recreate this planetarium by discussing the gear system, general set up, and control system.

Step 1: Step 1: Parts and Tools

Step 2: Step 2: Creating the Gear System

Here is where the 3D printer comes into play. You will need to download the attached STL files to 3D print the gears and a base that will hold the gears and rods in place. The planetarium design consists of 4 gears: The Motor gear (drive gear), the Earth gear (driven gear), a small central gear, and the Moon gear. The Motor gear will be attached to the stepper motor and will drive the Earth gear. The Moon gear will be on top of the Earth gear and will have a rod at its center which will go through the Earth gear. This will cause the Moon gear to turn as the Earth gear turns. The Central gear is used to hold the Moon gear in place and will go around the center of the Earth gear. The rod for the Moon will run through the Moon gear which will allow the moon to travel around the Earth while both the Earth and the Moon travel around the Sun. To save on printing time, I used an infill of 5% on the base. This low infill also made the base very light which was beneficial.

Step 3: Step 3: Prep Work

Rod prep

Once everything is printed, we will have to do some prep work to get our planets, rods, and enclosure ready for installation. First, we will need to use the band saw to cut the rod into three parts. One should be 5", one is 3", and the last is 1.5".

Planet Prep

We will be using the doll heads and ball bearing to create our Earth, Sun, and Moon. The 1.5" head will be used for the Sun, the 1.25" head for the Earth, and the ball bearing for the Moon. First you want to drill holes into the flat bottom of the doll heads using the 3/8" drill bit. This will allow you to attach the planets to the rods. Now comes the fun part, painting! Depending on what paint you use, you may need to apply several coats to get a vibrant color, especially when painting the Sun and Moon. Remember, its better to apply several thin coats than it is to glob on one very thick coat. A thick coat will likely cause drips and will take a long time to dry. Be sure to let each thin coat dry fully before proceeding. The Earth was painted freehand. Once the Moon is completely dry, Use the epoxy to attach it to the rod.

Enclosure Prep

We need to cut out a hole in the lid of the enclosure to allow the rods to move freely. For this, you will need to use the 4" hole saw attached to the drill. Remember that the hole needs to be offset from the center to provide room for the stepper motor and motor gear. Use your base as a reference to determine where to cut the hole and make sure its centered with the edges of the enclosure.

Now that your planets, rods, and enclosure are prepped, you are ready to start assembling!

Step 4: Step 4: Main Assembly

Start by placing your stepper motor into the allotted slot in the base. Make sure to tuck in the wires so that they run down through the base and out the bottom. Next place the Earth gear onto the extruded tube on the base. You want to position the Earth gear so that it floats just above the base and will not rub on it when turning. Now place the Motor gear onto the stepper motor so that the center of the gear runs through the shaft of the motor. The Motor gear and Earth gear should fit together nicely. Next, add the Central gear to the extruded tube. The central gear will have a very tight fit on the extruded tube and will need to be hammered into place.

Note, it is very difficult to remove the Central gear once it is hammered into place so make sure you have adequately positioned everything underneath it before proceeding. You also want to leave a little room between the Earth gear and the Central gear so that they do not interfere with one another.

You are now ready to add your rods. The Sun rod will go into the extruded tube on the base and the Earth rod will go through hole in the Earth gear. Again, make sure that there is no rubbing between parallel parts. The Moon gear is then placed around the Earth rod, on top of the Earth gear. The Moon rod will go into the secondary hole on the Moon gear. Top off your rods with their respective planets and you are ready to move on to the circuit schematic.

Step 5: Step 5: Circuit Schematic

The main parts to the schematic are the microcontroller, the power supply, the stepper motor and driver board, and the sound sensor.

Power Supply

The power is supplied by a 9V battery that attaches to the microcontroller.

Stepper Motor & Drive Board

The stepper motor is connected to pins 8,9,10, and 11 on the microcontroller. These pins are used to activate coils 1-4 of the stepper motor. They are defined as outputs in the sketch.

Sound Sensor

The sound sensor is attached to pin 4 on the microcontroller. It is defined as an input in the sketch.

Step 6: Step 6: the Arduino Sketch

As previously mentioned, pins 8 -11 are connected to the drive board (shield) and will activate coils 1-4 of the stepper motor. The sound sensor is connected to pin 4. I have defined a delay time of 8 ms to yield a reliable turn rate by the stepper motor. In the setup, I have defined the motor pins as outputs and the sound sensor pin as an input. The sound sensor is read in the main loop by a status variable names statusSensor. When a noise is detected, the status sensor will by set to 1. This will start turning the motor forward for 300 steps. A while loop is used to count the steps. If a new sound is detected, the count will restart causing the motor to turn for a longer period of time. If not sound is detected, the motor will stop turning after 300 steps. Please see the attached video for more information.

Note: You can set any number of steps for the motor to turn. I found that 300 steps yields about 30 seconds of motion. Feel free to change up the step count if you would like the planetarium to run for a longer or shorter period of time.

Step 7: Step 7: Enclosure Assembly

All that is left now is to put all of the components into the enclosure. I found that this was most easily and effectively accomplished using velcro strips. First line the bottom of enclosure with the hook (rough side). Next line the bottom of your breadboard, microcontroller, sound sensor, motor, motor shield, and battery with the loop (soft side). Add a loop to the top of the breadboard to hold the motor in place. You may now securely place each remaining component in the enclosure. To attach the base, first cut out two pieces of the loop that are slightly larger in length and width than the long sides of the base. Attach each strip to the long side of the enclosure positioned in a way that will allow the stepper motor gear to be fully enclosed and the Earth gear to fit nicely within the hole that was cut out of the enclosure lid. Mine were placed approximately 1" from the top of the enclosure. Next attach two matching hooks to the long sides of the base. You may now attach your base to the enclosure. I chose to elevate the base in this way to provide room for the circuitry underneath.

Your planetarium is now fully assembled and ready for use! Make sure that your battery is connected to the microcontroller, apply the screws to the enclosure, and let nice loud noise. You should see your planetarium begin to move.

Note: for better sound detection, hook your sound sensor to one of the walls of the enclosure near the cut out in the lid.

Step 8: Final Remarks

Although this was a simple project, the knowledge I've gained from it is invaluable. I've learned all about 3D modelling, coding microcontrollers, video editing, project planning and so much more. I've also gained a lot more respect for product designers because there is a lot of thought and effort that goes into designing something and bringing those designs to life. A Lot of trial and error and a lot of problem solving. It was fun to involve myself in the process.

Hope you enjoyed this instructable!