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Electronics Projects: How to Use a Piezo Speaker with a BASIC Stamp

You can add interesting sound effects and simple music to your electronics projects using the BASIC Stamp Activity Kit. The kit comes with a small piezoelectric speaker, which you can connect directly to an I/O pin to create beautiful music.

Well, the music probably won’t be so beautiful, but you can coax the BASIC Stamp into emitting a variety of squeaks, burps, and squelches that resemble musical notes. And you can create interesting sound effects like police sirens or chirping crickets.

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If you didn’t purchase the BASIC Stamp Activity Kit, you can order the piezo speaker directly from the Parallax website (www.parallax.com) for $1.95.

Note that the piezo speaker is polarized, so when you connect it to an I/O pin, be sure to connect the + terminal to the I/O pin and the other terminal to Vss (ground).

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Program with the FREQOUT command

Programming a piezo speaker is remarkably simple. PBASIC includes a command called FREQOUT that sends a frequency of your choice to an output pin. Thus, you can create an audible tone on a piezo speaker by using the FREQOUT command, using the following syntax:

FREQOUT pin, duration, frequency

Here's how that syntax works:

  • pin is simply the pin number that you want to send the frequency to.

  • duration is simply the length of time in milliseconds you want the frequency to play. And

  • frequency is the frequency in hertz that you want to generate.

For example, the following command generates a 2,000 Hz frequency for five seconds on pin 8:

FREQOUT 8, 5000, 2000

You can easily create a beeping sound by alternately sending short bursts of a frequency to the speaker followed by a brief pause. For example:

DO
 FREQOUT 8,250, 1500
 PAUSE 250
LOOP

This code repeatedly sends a 1,500 Hz signal for a quarter of a second, and then pauses for a quarter of a second. The result is a beep-beep-beep sound.

Test the piezo speaker

This project shows how to build a simple circuit that connects a piezo speaker to a BASIC Stamp so you can create audible output; two pushbuttons vary the sound output.

The piezo speaker here is actually very quiet. This is normal; the piezo speaker draws just 1 mA, and so can’t make a lot of noise. The speaker is loudest with frequencies between 4,500 and 5,500 Hz.

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