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Audio Tone Generator

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Recipe #29 — audio tone generator

The same 555 oscillator becomes an audio generator when its RC timing values are reduced enough to make hundreds or thousands of cycles per second.

555 AUDIO TONE GENERATOR 555 2,6 TIMING7 DISCH3 OUT1 GND +9 V R1 4.7 kΩ P1 100 kΩ PITCH C1 0.01 µF C2 1 µFPIEZO / HIGH-Z SOUNDER Same oscillator idea — smaller timing values move the repetition rate into the audio range.
Turn P1: the oscillation frequency changes. At tens or hundreds of hertz the pulses become a clearly audible tone rather than separate clicks or flashes.

Frequency is just repetition rate

The metronome and tone generator are the same kind of oscillator. The difference is only how fast they repeat. Human hearing interprets fast repetitive pressure changes as pitch.

This is a square-wave tone

The 555 output switches sharply between two voltage levels, so it contains a fundamental frequency plus many harmonics. That gives the tone a buzzy character. A sine-wave oscillator produces a much smoother sound.

A small piezo or high-impedance sounder is easier for the 555 to drive than an 8 Ω loudspeaker. A low-impedance speaker normally deserves a separate driver stage.

555 wiring reminder: in a real build, tie RESET pin 4 high when unused, provide supply decoupling close to the IC, and treat pin 5 CONTROL as the datasheet recommends.

Try these yourself

How is this different from the 555 metronome?
The same astable idea is simply adjusted into the audible frequency range.
Why does a 555 tone often sound buzzy?
A square wave contains many harmonics in addition to its fundamental frequency.
Why avoid driving an 8-ohm speaker directly in this simple example?
A low-impedance speaker can require more output current than the simple timer stage should supply comfortably.
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