Elenco 130-in-1 Electronics Playground - Manual (Page 111)

-111-
This burglar alarm makes a buzzing sound when
anyone sneaking into your house trips over a wire
and breaks it off or disconnects it from a terminal. Try
to figure out how to connect a switch to the door of
your house, so that the alarm sounds when a burglar
opens the door, instead of stretching out the wire.
Start by sliding the switch to position B and
assembling the circuit. When you complete the
wiring, connect the terminals 13 and 14 to the long
wire, and slide the switch to position A to turn on the
power. No sound comes from the speaker, at this
time.
Detach the wire from terminal 13,to test the alarm.
The speaker gives out a beep. This beep is the alarm
that tells you a burglar is about the break into your
house.
As you can observe in the schematic, this burglar
alarm uses the operational amplifier as an astable
multivibrator, as the electronic buzzer in the last
experiment did. You can change its frequency by
using different values for the 10k
Ω
k k resistor and the
0.1
μF capacitor. Note how the tone of the buzzer
alters when you set the 10k
Ω resistor to 47kΩ or
switch the 100k
Ω and 220kΩ resistors with each
other.
Notes:
EXPERIMENT #92: BURGLAR BUZZER
Schematic
Wiring Sequence:
1-29
2-30
3-114
5-14-83-70-110-121
13-89-68109
81-63-132
67-90-92-113
69-82-84-91
119-124
122-131
13-14 (LONG WIRE)