Elenco Electronics EP-130, Manual, Page: 70 / 160

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Here’s another circuit that uses both transistor and
NAND type multivibrators. It allows you to see LED
1 light up at the same time you hear a sound
through the earphone.
When you finish building this project, connect the
earphone to terminals 13 and 14 and set the switch
to position A. You’ll hear a pulse in the earphone
each time the LED lights up. Do you know why this
happens?
Assume the output of the NAND multivibrator is 0,
and trace that output from the NAND multivibrator to
the transistor multivibrator. Do you think the
operation of the transistor multivibrator is affected
by the NAND multivibrator? If you say yes, how is it
affected?
Try using other electrolytic capacitors in place of the
100
μ
F capacitor in the NAND multivibrator to see
what effects they have on the circuit. Try changing
the transistor multivibrator and see how you can
alter its operation.
You can use the speaker instead of the earphone
with this project by connecting the NPN transistor,
the output transformer, and maybe a resistor or two.
Try adding the speaker – but be sure to write down
the new circuit you design.
Notes:
EXPERIMENT #53: BUZZIN’ LED
Wiring Sequence:
o
31-55-56-57-76-116
o
33-59-60-62-72-80-121
o
40-109-85
o
131-45-42-49
o
43-105-81
o
50-51-77-115
o
52-53-54-75-78
o
58-82-86
o
119-132
o
110-44-71-13-EARPHONE
o
106-41-79-14-EARPHONE
Schematic