In this chapter, we will build a configurable MIDI-controlled xylophone-like instrument made with empty glass bottles and a set of servos. This will make use of almost all of the Pi's GPIO headers to drive the servos.
The servos are controlled using a web application that allows you to upload a MIDI file, set a temp, and allows the Pi to play the file on the bottles using a configuration file to tell it which bottle is tuned to which note. The tuning itself is done by varying the level of water in each bottle.
Since this project requires a lot of GPIO pins, you may wish to opt for a B+ model, which has an additional nine GPIO pins on its 40-pin connector.
For this project, you will need the following:
- The Raspberry Pi B+
- A small section of a prototyping board
- USB power supply and a micro USB cable
- High current 5 V power supply
- Several 1000 uF capacitors (www.maplin.co.uk/p/1000f-35v-85c-radial-electrolytic-capacitor-vh51f)
- A breadboard (www.maplin.co.uk/p/ad-100-breadboard-ag08j)
- A strip of 0.1-inch pin headers
- 0.1-inch male-to-female pin jumpers
- M3 nuts and machine screws
- Cable ties
- 15x empty glass bottles
- 15x micro servos
- A 15x servo mount base
- A 15x servo mount
I found that the larger 500 ml bottles are better for this as opposed to the 330 ml ones. Anything larger then 500 ml will still work; however, they may not fit on the servo mount base correctly (this should not stop the servo from working correctly).
To make tuning easier, it is recommended that you use the same size bottles for all the 15 notes.
The amount of capacitors you will need is determined by the power output of the power supply you are using and the number of servos you have; at least five capacitors are recommended for this. The power supply should be rated for at least 2 A to ensure reliable operation.