Elenco 130-in-1 Electronics Playground - Manual (Page 105)

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The operational amplifier (op amp) works well as an
oscillator. In this experiment, you will build an electric
buzzer that makes a continuous beep. By rotating the
control you can change the tone of this buzzer.
When you finish the wiring, set the control to the 12
o’clock position and press the key. From the speaker
you hear a continuous beep. Turn the control as you
press the key; the tone of the buzzer changes.
The electronic buzzer only makes a beep, but it can
be used for many different purposes, as you’ll see
later.
This circuit is an astable multivibrator working as an
oscillator to produce a square wave signal for the
speaker. Adjusting the control changes the
frequency, so the tone of the sound is different. The
frequency is determined by the resistors and
capacitor connected to the input terminals of the
operational amplifier. Try changing the capacitor to
0.02
μF or 0.1μF and see how the tone changes.
Notes:
EXPERIMENT #86: BUZZIN’ WITH THE OP AMP
Schematic
Wiring Sequence:
1-29
2-30
3-116
5-84-70-106-121
63-27-138
28-81
67-90-92-115
91-68-105
69-82-83-89
119-124
122-137