Elenco 130-in-1 Electronics Playground - Manual (Page 142)

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When you connect the signal from this oscillator to
an oscilloscope, it creates a pattern that looks like
the teeth of a saw (as shown below).
The shape of this wave results from the slow
charging of the 0.1
μF capacitor through the control
and the 100k
Ω resistor, and the capacitor’s
discharge through the PNP and NPN transistors.
The voltage divider - the 470
Ω and 100Ω resistors -
provides about 1.6 volts to the transistors. Current
flowing from the 9V supply into the 0.1
μF capacitor
(through the control and the 100k
Ω
k resistor) slowly
charges up the capacitor. When the capacitor’s
charge exceeds the voltage of the voltage divider
(1.6V), the transistors turn on and provide a path for
the 0.1
μF capacitor to discharge quickly. Now, the
transistors turn off again, and the capacitor begins
to slowly charge to repeat the cycle.
You can modify the oscillator frequency by changing
the values of the components in the timer circuit - the
control, the 100k
Ω
k k resistor and the 0.1
μF capacitor.
Try a 47k
Ω resistor or a 220kΩ resistor in place of
the 100k
Ω resistor, and try several different
capacitors. If you connect one of the electrolytic
capacitors, be sure that you use the proper polarity
(+ and –).
Notes:
EXPERIMENT #120: SAWTOOTH OSCILLATOR
Schematic
Wiring Sequence:
73-81-27-119
28-89
71-74-47-40
41-46
42-43-90-109
124-44-48-110-72-EARPHONE
45-82-EARPHONE
121-122