70009 Parallax Inc, 70009 Datasheet - Page 44

• Manufacturer Part Number: 70009
• Description: BOOK UNDERSTANDING SIGNALS
• Manufacturer: Parallax Inc
• Type: Signal Analysisr

Specifications of 70009

• Style: Book
• Title: Understanding Signals
• Contents: Guide to Generate, View and Measure Wave Forms
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Other names: 70009PAR

Note the ratio of on-time vs. off-time as the signal progresses from left to right. You can
see that the on-time is progressively increasing while the off-time is progressively
decreasing. If this signal were filtered into a smooth DC signal, we would see an analog
voltage starting close to zero and growing to a voltage close to 5 VDC. So, as the duty
cycle increases, the average DC value increases. This is the fundamental principle upon
which the BASIC Stamp recreates sine waves.
Using the PWM output from the BASIC Stamp, a small RC filter, and a piezo speaker,
you can create a sequence of square waves, sine waves, and sound waves that are
viewable on the OPTAscope.
ACTIVITY #1: SINE WAVE SURFING
The goals of this activity are to:
Parts Required
(1) Piezo speaker
(1) 220 Ω resistor
(1) 1.0 µF capacitor
(6) Jumper wires
Building the Sine Wave Measurement Speaker Circuit
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Create a sine wave.
Capture and view it on the OPTAscope.
Vary the frequency of the sine wave and note the change in pitch and volume.
Experiment with the trigger level.
Build the circuit as defined by the schematic in Figure 3-3. Awiring diagram of
the circuit is shown in Figure 3-4. If using the HomeWork Board, omit the 220 Ω
resistor as one is already built in; replace with a jumper wire to make the
necessary connection.
WARNING: The 1.0 µF capacitor can explode if it is connected improperly!
Always disconnect the power before building or modifying circuits. Carefully check the
polarity of the 1.0 µF capacitor. The positive terminal (longer leg) must be connected to a
power source pin and the negative terminal (shorter leg) must be connected to Vss (ground).