Elenco 130-in-1 Electronics Playground - Manual (Page 109)

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This siren gives off alternating high and low sounds.
Slide the switch to position B and construct the
circuit. After you complete the wiring and slide the
switch to position A, the power turns on and the
speaker creates the sound of a two-pitch siren.
This siren is made up of two astable multivibrators.
IC 2 provides the normal beep sound. IC 1 produces
the signal that alters the pitch of its sound at regular
intervals.
Let’s execute a small experiment now. The siren
gives out an intermittent beep instead of the two-
pitch sound once you detach the 22k
Ω k resistor. Can
you decipher why? The IC 1 interrupts the siren
sound produced by IC 2.
Notes:
EXPERIMENT #90: CRISIS SIREN
Wiring Sequence:
1-29
2-30
3-116
5-83-70-108-112-121
85-63-131
64-90-92-115
65-107-89
66-82-84-86-91
81-94-88-67
93-68-111
69-80-87
79-119-124
122-132
Schematic