Elenco PK101 w/ Computer Interface - Manual (Page 9)

Move the variable resistor knob and watch how it changes the waveform on the computer screen.
Now click on the 0.5ms/div button to change the time scale on the display. (The button to the left of it
is for 5ms/div, the default.) Move the variable resistor knob around again. You may click on the Hold
button to freeze the waveform on the screen, then click on On-Line to re-start.
With the time scale at 0.5ms/div
and the adjustable resistor set for
middle position, you should now
have a picture similar to this one.
Your picture may appear different
due to variations in the micro-
phone input designs between
computers. Although this is
beyond software control, in some
cases you may be able compen-
sate externally. See notes B and
C on page 4 for details.
Notice that the waveform seems to be randomly dancing across the screen, making it hard to study.
We can fix this. Click on the “trigger positive level” button and make sure the trigger bar is in the
position shown here. Notice that a small “-” appears on the left of the display as you do so.
The small slash “-” represents the
trigger voltage, when the signal
reaches this voltage level it acti-
vates the display. This makes it
easy to observe a stream of puls-
es like you have now, and also to
record a single (non-repeating)
pulse.
Move the variable resistor control
and watch how it changes the
waveform on the computer
screen. Now you can see how
changing the variable resistor
changes the time between the
pulses, which changes the tone of
the sound you hear.
The waveform you see here is the voltage across the speaker, the peaks of the pulses occur when
the transistors turn on and provide current to the speaker. Changing the amplitude of the peaks
changes the loudness of the sound, changing their separation changes the tone or “pitch” of the
sound. The time scale and trigger control features just described enable electronics engineers and
technicians to see the relationship between parts of a waveform on their oscilloscope.
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