Elenco 130-in-1 Electronics Playground - Manual (Page 80)

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This circuit is an oscillator with a slow frequency, and
you can see the LED lighting and turning off. The off
time is longer than the on time, so you observe short
pulses of light with long periods between them. The
wiring sequence below will make the decimal point
light, however you can light any part of the LED
display.
This type of circuit is known as a sawtooth wave
oscillator, because the electrical waveform of the
signal looks like a sawtooth pattern between two
voltage values. The signal alters as the LED lights
and turns off. Shorter pulses are generated when the
output from the emitter of the PNP transistor supplies
the base current to the NPN transistor (as in this
circuit).
Try experimenting by altering the value of the 3.3
μF
capacitor to 10
μF. You can also differ the 1kΩ resistor
and alter the 470k
Ω resistor to 220kΩ. The rate of
charge and discharge of the capacitor controls the
frequency of this oscillator. Changing its value or the
values of the resistors that supply current to the
capacitor alters the frequency.
Notes:
EXPERIMENT #62: DECIMAL POINT STROBE LIGHT
Schematic
Wiring Sequence:
o 47-40-25-89
o 41-46
o 42-76
o 90-112-48-120
o 75-94-111
o 93-119-24
This is the electronic bird circuit that you built for
Project 6 (The Woodpecker), but now it has a
photoelectric control of the transistor base. This
circuit is activated by light, so you can use it as an
early bird wake up alarm.
To make the sound of the bird, press the key. You can
modify the control so that the right amount of light
will set off the bird and wake you up in the morning
– not too early and not too late.
From the original electronic bird, we have changed
only a few component values, and rearranged the
circuit schematic. See if you can find the changes and
rearrange the circuit so that it looks like Project 6. Use
the space provided to redraw the schematic.
Notes:
EXPERIMENT #63: “THE EARLY BIRD GETS THE WORM”
Schematic
Wiring Sequence:
o 1-29
o 2-30
o 3-107-109
o 4-27-137
o 5-41-110
o 15-88
o 16-28
o 76-87-106-40
o 119-42-115
o 75-116
o 105-108
o 120-138