Piano Stairs with Arduino and Raspberry Pi

Who doesn't love music? These Piano Stairs are an interactive, relatively portable, musical installation that can be applied to basically any stairwell. I built them for HackPrinceton along with my friends Erica Portnoy and Vincent Castaneda, and we won 2nd place in the hardware track. I've had requests to share my code and diagrams, so I decided to make an Instructable!

These piano stairs use a light-based "tripwire" for each stair. The light sources should be on one side of the stair, the photoresistors on the other. In this setup, the Arduino reads from the sensors and passes the values to the Raspberry Pi, which generates the sounds.

What you need, assuming six stairs:
6 photoresistors
6 resistors, 1000 ohms each
6 light sources: I used flashlights, you can use bright LEDs
1 standard speaker set, w/ audio cable
1 breadboard
Soldering iron
1 Arduino Uno
1 Raspberry Pi

Step 1: Learn to read a light sensor from the Arduino

Piano Stairs with Arduino and Raspberry Pi
Youíll want to follow Adafruitís photocell tutorial for this.

I suggest that you first get your basic light sensor circuit set up, using a breadboard and an Arduino, so that you understand how the basic light sensing works. The image for this step is the basic diagram you'll need. Come back once you can read a photoresistor using your Arduino!

Step 2: Solder your photoresistor circuits

Piano Stairs with Arduino and Raspberry Pi
Piano Stairs with Arduino and Raspberry Pi
Piano Stairs with Arduino and Raspberry Pi
OK, now that you understand the basic idea, we need to solder 1 photoresistor circuit per step of the staircase. Iím assuming 6 steps here. Youíll want 1 sensor per step, with them all connecting at the bottom of the stairs.

Now, for each photoresistor, youíll want to do the following:
I found it useful to use cardboard backing to keep the photoresistors stable. Stick the legs of the sensor through and tape them in place with electrical tape.

Solder one short ground wire to one leg of the photoresistor.

Solder one "power" wire to the other leg. This wire should be long - based on the height of the stairs, and which stair this sensor is for. It should reach all the way to the bottom of the stairs.

Mark the stair number on the piece of cardboard, and tag the end of the power wire with the stair number as well (using masking tape and a marker). This will help you later.

Step 3: Solder the ground wire, connect everything to the Arduino.

Piano Stairs with Arduino and Raspberry Pi
Piano Stairs with Arduino and Raspberry Pi
Piano Stairs with Arduino and Raspberry Pi
Now, take a really long wire, strip it in appropriate places, and solder each short ground wire to the long ground wire. Plug this into your Arduinoís ground pin (labeled GND).

Connect a wire from the power output pin of your Arduino (5V) to a power row of your breadboard.

For each "power" wire from a photoresistor circuit, connect it to some unused row n in the breadboard. Also to row n, connect a wire to analog pin n on the Arduino. Finally, connect a resistor from row n to the power row of your breadboard.

This should be practically identical to the basic photoresistor circuit you built earlier! It's just 6 of them on one breadboard.

Make sure to connect the wires in a logical order. E.g., stair 1 should go to Pin 1, stair 2 to pin 2, etc. Otherwise your notes will be out of order.

Step 4: Setup the staircase

Piano Stairs with Arduino and Raspberry Pi
Masking tap, twist ties, flashlights; this is when you can actually set stuff up. Tape each piece of cardboard to one stair. Across from it, position a flashlight so that the light beam falls directly on the photoresistor.

Step 5: Upload the Arduino code

The provided Arduino code is designed to print out a stream of numbers to Serial. It auto-calibrates itself. Upload the provided code, let it calibrate, then test it by reading the Serial output.

It prints out lines of 6 digits (ones and zeros):

..this means that a footstep has been detected on steps #1 and #4 (if weíre counting with step #1 on the left-hand side of the output).

Get the code here:
(Look in the piano directory for piano.ino)
Piano Stairs with Arduino and Raspberry Pi
piano-stairs.zip25 MB

Step 6: Connect to Raspberry Pi

Piano Stairs with Arduino and Raspberry Pi
Plug the Arduino into the Raspberry Pi via the USB cable. Then, plug your speakers into the Raspberry Pi's audio jack.

Download the github repo onto your Raspberry Pi and run python ohboymusic.py!


Image from raspberypi.org

Piano Stairs with Arduino and Raspberry Pi
piano-stairs.zip25 MB

Step 7: Enjoy, Tweak, Tinker

Congratulations! You should have a working set of piano stairs.

Troubleshooting tips:
You can hit the red "reset" button on your Arduino to recalibrate the light thresholds. Make sure nobody is on the stairs, and that the flashlights are turned on, when you do so!


Isnít it wasteful to use an Arduino and a Raspberry Pi? Why do you need both?
Yeah, it is, but I did this for a hackathon and this is what I had on hand! You could use an Analog to Digital Converter (ADC) and a Pi Cobbler Breakout Board in order to replace the Arduino entirely. (The RPi only has digital pins, alas, so you need an ADC - but thatís cheap.) Hopefully Iíll have an updated version posted soon, because I have an ADC coming in the mail.

This code is crap!
Iím supplying the code I used in the hackathon, so itís a bit messy. Iím waiting to clean it up until I can switch to using an ADC and get rid of the Arduino entirely.

Can I expand the # of stairs?
Right now Iíve maxed out the number of analog pins on an Arduino. So yes, you could, and that would be awesome, but would require significant modifications.

Why flashlights?
You could also try using LEDs, or infrared sensors. But you need some kind of light source so that you can clearly differentiate, say, a sneaker, from just a shadow on the staircase.


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