Manual 7 Second Timer (Ii); 15 Second Alarm - Elenco Electronics Snap Circuits Instruction Manual

Project #433
Project #434
Manual 7 Second
Timer (II)
OBJECTIVE: To build a manual timer using a relay and whistle
chip.
This circuit is similar to project 431 except now the whistle chip (WC) will
also make sound.

15 Second Alarm

OBJECTIVE: To build a circuit that sounds the speaker for 15
seconds.
As in project 431, the transistor (Q2) acts as a switch, connecting the
relay (S3) and the alarm IC (U2) to the batteries. As long as there is
a voltage on the transistor's base, the alarm IC sounds.
Turn on the switch (S1) and then press the switch (S2). The transistor
turns on, the capacitor (C5) charges up, and the alarm sounds.
Release the press switch (S2). As the capacitor discharges, it keeps
the transistor on. The transistor will turn off when the capacitor is
almost discharged, about 10 seconds. The relay contacts will switch
and the alarm will turn off .
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