Elenco Upgrade Kit SC300 to SC750 - Manual (Page 47)

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Project #445
Alarm Timer (II)
OBJECTIVE: To change the time by switching the resistor and
capacitor.
Project #446
Alarm Timer (III)
Build this circuit
using the following
combinations for R5
and C5:
R5 & C3, R4 & C4,
and R4 & C5.
OBJECTIVE: To modify project #285 for a different sound.
Project #444
OBJECTIVE: To connect the alarm IC to a timer circuit.
Alarm Timer
Turn on the slide switch (S1) and the alarm may sound and slowly drift
away as the lamp (L2) brightens. Press the press switch (S2) and the
alarm sounds at full volume as the LED (D1) lights. Capacitor C5 is
also charged. Release the press switch; the alarm IC (U2) still sounds
because the voltage from the discharging C5 keeps Q1 and Q2 off. As
the capacitor’s voltage drops, the LED will turn off and the sound will
slowly stop.
Replace resistor R5 and capacitor C5 with different values and see
how it affects the circuit.
Replace the 1-snap
wire from the middle
snap on U2 with a 2-
snap and connect it
to grid location D7 &
E7. The circuit now
produces a different
sound. Change R5
and C5 with the
following combin-
ations for R5 and C5:
R5 & C3, R4 & C4,
and R4 & C5.