-62-
Do you know what this circuit will do? Connect the wires
according to the Wiring Checklist (noting that the
transistor bases are not connected although their wires
cross in the schematic). Press the switch and release it.
The LED is on for a few seconds and then goes out.
What effect do you think changing the value of the
variable resistor will have? Try it. The higher the
resistance the longer the LED stays on.
This circuit is a variation of the astable multivibrator and
is called a one-shot multivibrator, because the LED
comes on once each time the switch is pressed. The
33KW, variable resistor, and 100mF control how long the
LED is on. This circuit can be used as a timer. You might
use a circuit like this with your microwave oven. You
press the switch to turn the oven on and have a knob (the
variable resistor) to adjust how long the oven stays on; it
then shuts off automatically.
EXPERIMENT #43: One-shot
Wiring Checklist:
o 40-to-1
o 2-to-16-to-36-to-56
o 17-to-20-to-26-to-55
o 37-to-49-to-18
o 46-to-48
o 44-to-42-to-19
o 15-to-45
o 41-to-43-to-47-to-27
Schematic
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