Servo - March 2012

Sounding Off

Adding Sound to Your Arduino Robot

by Gordon McComb

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My first robot with sound used the mechanism from an old cassette recorder. Music and sound effects were stored on short tapes. The whole thing was mechanically driven with a solenoid that turned the PLAY button on and off. The biggest problem: There was no way to know what musical jingle the robot was going to play next.

Thanks to several ready-made add-on boards for the Arduino and other popular microcontrollers, you can incorporate melodies, effects, and other sounds to your robots. You have full control over what’s played — from

FIGURE 1. Pulse width modulation is a common technique for making sound using a digital output. By using pulses within the range of human hearing (about 20 Hz to 20 kHz) and changing the timing of the pulses, the signal is heard as a sound tone.

short quarter-second gunshots to 10 minute lullabies.

In this article, you’ll read about how to give your mechanical creations completely electronic sound effects, music, and even voice. The subject of robotic sound is a large one, and a single installment isn’t enough to address everything. So this time around, I’ll cover basic sound generation using just the Arduino — with and without external amplification — plus adding low cost effects, music, and voice co-processor chips to simplify the noise making.

Next time, I’ll cover even fancier sounding off methods, including playing WAV, MP3, and other digital files, making music with MIDI, and building your own sound co-processor.

Important note: The demo code in this article is intended for the Arduino 1.0 integrated development environment (IDE). If you haven’t already, be sure to download the latest Arduino IDE software. You can install it side-by-side with any previous version you already have. This is recommended, since some Arduino examples you’ll find on the Web may not yet be compatible with the 1.0 software.

The Sound of Arduino Music

Any microcontroller with a pulse width modulation (PWM) feature can be used to produce sound effects and music. PWM is a series of pulses as shown in Figure 1; when the pulse frequency is within the range of hearing — about 20 Hz to 20 kHz — it comes out as a tone. The sound is heard by passing the pulses by way of the microcontroller’s I/O pins through a speaker or amplifier.

By varying the frequency of the PWM, you make high, middle, and low tones. You can produce music with one PWM output (that’s called monophonic), or you can combine the outputs of two or more PWM

FIGURE 2. Attach the piezo element directly to the Arduino I/O pins. To simplify the connection (so the two wires from the speaker are next to each other), I'm using one of the pins as ground. Refer to the sketches for how this is done.