Manual

-106-
T
he electronic buzzer we built in the previous circuit
can only make a continuous beep, but we can make
a similar circuit that produces various siren sounds.
Y
our going to make a siren that gives out a sound
with a variable pitch. When you move the switch,
this siren wails and then creates a continuous high-
pitched noise.
Slide the switch to position B and assemble the
circuit. When you complete the wiring, turn the
power on by sliding the switch to position A. You
hear the speaker produce a sudden, roaring siren
sound. At first the sound is low and becomes higher,
then changes to a steady tone in about 3 to 4
seconds. When you press the key and release it,
the capacitor discharges and starts the siren sound
again.
You can understand how this works by looking at
the schematic. The pitch changes as the 10mF
capacitor is charged through the 100kW resistor. IC
2 is an astable multivibrator. IC 1 is a buffer between
the capacitor and IC 2.
N
otes:
EXPERIMENT #87: SWEEP OSCILLATOR
Wiring Sequence:
o 1-29
o 2-30
o 3-116
o 5-84-70-106-114-137-121
o 89-63-131
o 64-88-92-115
o 65-87-105
o 66-82-83-91
o 68-67-81
o 90-69-113-138
o 119-124
o 122-132
Schematic
EP-130_62315RevC.qxp_EP-130_062812 6/23/15 11:17 AM Page 106