Manual

-128-
W
ouldn’t you like to make a kitchen timer that you
can use for cooking meals? This circuit gives out a
buzzer sound for 1 to 2 seconds and automatically
s
tops.
Slide the switch to position B, build the circuit, and
set the switch to position A to turn it on. Set the
control to position 2 on the dial, and press the key to
start the timer. After about 40 seconds, the timer
sounds for 1 to 2 seconds and stops. Use the graph
you made in project 107 to preset this timer.
Look at the schematic. When the preset time is up,
the comparator (IC 2) sends out an output. After a
time lag of 1 to 2 seconds produced by R and C, the
transistor Q1 turns on to stop the multivibrator. The
silicon diode discharges C and restores the circuit to
the original state when the timer is restarted.
N
otes:
EXPERIMENT #108: COOKING TIMER
Wiring Sequence:
o 1-29
o 2-30
o 3-114
o 5-83-70-104-116-118-137-48-26-121
o 27-68
o 93-63-28-131
o 46-85
o 91-103-65-47
o 92-88-64-113
o 81-84-87-66
o 67-82-89
o 69-94-117-138-129
o 86-90-115-130
o 119-124
o 122-132
Schematic
EP-130_62315RevC.qxp_EP-130_062812 6/23/15 11:18 AM Page 128