Elenco PK101 w/ Computer Interface - Manual (Page 11)

Set the variable resistor control to mid-range. In addition to the 5ms/div and 0.5ms/div settings for
the horizontal scale, there is also a variable setting. See if you can set it so that all the signal peaks
line up with the grid lines, as shown.
As you can see, all the peaks are
equally spaced in frequency.
Move your computer mouse
directly over the first peak, the
software displays the frequency
you are pointing at. Move the
mouse to the other peaks and you
see they are multiples of the first
frequency.
Now you can see that the tone you hear is actually a range of related frequencies combined togeth-
er. The first peak is considered to be the main signal (and it is usually but not always the highest),
the energy at all the other peaks determine the waveform of the signal you see on an oscilloscope.
Now modify your circuit by replacing the 0.047
µ
F capacitor on top of the 10
µ
F capacitor (+ side to
breadboard point a10). By increasing circuit capacitance, you lower the oscillation frequency and
your display should now look something like this:
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