Even though the Propeller chip can play WAV files and synthesize speech, sometimes a simple beep is all the noise you need to get the job done. Many devices beep to get your attention. Microwave ovens let you know your food is ready, alarm system keypads respond when you press a number key, and smoke alarms warn you something is burning. These devices often use piezospeakers because they are inexpensive, yet make clear, audible tones.
The first breadboard circuit we'll build for the ActivityBot is a simple piezo speaker.
(1) Piezo speaker (#900-00001)
(2) Jumper wires
It is very easy to make this speaker beep with a single line of code:
freqout(4, 1000, 3000); // pin, duration, frequency
You can optionally add this line code at the beginning of your ActivityBot example programs. Then, If your robot's batteries run low, the Propeller microcontroller will reset and restart the program—the beep will let you know if this has happened. We include it because it can be very helpful when experimenting with navigation programs, and trying to figure out why your robot is behaving in an unexpected manner.
Let's try it.
The test code will make the piezospeaker beep for one second with fairly high-pitched tone.
The freqout function has parameters of pin, msTime, and frequency. The function call freqout(4, 1000, 3000) sends an alternating high/low signal to pin 4, for 1000 ms (or 1 second), at a frequency of 3000 Hz (3000 times per second). Since the speaker is connected to P4, this rapid 3.3 V to 0 V high/low sequence makes the piezoelectic element in it vibrate 3000 times per second. The result is a high-pitched tone.
/* Piezo Beep.c Beep a piezo speaker connected to P4. */ #include "simpletools.h" // Include simpletools int main() // main function { freqout(4, 1000, 3000); // pin, duration, frequency }
If you want to make your code do something while it's broadcasting the tone, use the squre_wave function instead. It's the "set it and forget it" version of freqout. Check the simpletools library documentation for more info. You can find it at: ...\Documents\SimpleIDE\Learn\Simple Libraries\Utility\libsimpletools\Documentation simpletools Library.html
When you press a key on a piano, it makes a small hammer strike a tightly pulled wire, causing the wire to vibrate at a certain frequency. Here are the frequencies of some higher keys to the right side of the piano keyboard:
You can use an array to store note values, and then play them with a for loop. (See Array Variables [1] for a refresher.)
You can also use #define to give your frequencies note names, and then you can use those note names in your array in place of the numbers. It’ll make your digital composing a lot easier.
Links
[1] https://learn.parallax.com/node/620