The cyber:bot tone function

Let's test the piezospeaker using calls to the cyberbot module's tone function.  True to its name, this function instructs an I/O pin to alternate high/low electrical signals at a specific frequency, allowing a piezospeaker to emit a tone.

The tone function allows you to specify the frequency with the f parameter,  and the duration of the tone in milliseconds with the ms parameter.  

bot(22).tone(f, ms)

This piezospeaker is designed to play 4.5 kHz tones for smoke alarms, but it can also play a variety of audible tones and usually sounds best in the 1 kHz to 3.5 kHz range.  The start-alert tone we’ll use is:

bot(22).tone(3000, 1000)

That will make P22 send a series of high/low signals repeating at 3 kHz (3000 times per second).  The tone will last for 1000 ms, which is 1 second.  The micro:bit will wait until the tone function is complete before moving on to the next command. 

Example PiezospeakerTest.py

This example script makes a beep when it starts running, then it sends the message “Waiting for Reset” scrolling across the micro:bit LED matrix.  These messages will continue indefinitely because they are in the while True: loop.  If the reset button is pressed, the speaker will replay the sound.

  • Enter, save, and flash the script below:
# piezospeaker_test.py

from cyberbot import *

bot(22).tone(3000, 1000)

while True:
    display.scroll("Waiting for Reset")

 Try this: for loops for sound effects

It is easy to make sound effects by using a for loop.

  • Enter, save, and flash the script below.
# sound_effect.py

from cyberbot import *

for freq in range (500, 3100, 100):
    bot(22).tone(freq, 100)

You should hear a series of tones that increase in pitch.

Your Turn

Just for fun,  modify the sound_effect.py script by varying the values in the range function's start, stop, and step parameters.

  • Try making the tones cover a greater range of frequencies.
  • Try making the tones vary only a little from one to the next, for a smoother sound.
  • Try making the tones go from a higher pitch to a lower pitch, so it sounds like something is falling.
  • Try making a script that sounds like a cricket.