28119 Parallax Inc, 28119 Datasheet - Page 43

• Manufacturer Part Number: 28119
• Description: KIT UNDERSTANDING SIGNALS
• Manufacturer: Parallax Inc

Specifications of 28119

• Lead Free Status: Contains lead
• Accessory Type: Oscilloscope
• Interface Type: USB
• For Use With/related Products: BASIC Stamp® 2 and Board of Education
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Chapter #3: Sine Waves
SINE WAVES WITH THE BASIC STAMP FREQOUT COMMAND
A sine wave is a common electrical signal that can be viewed on the OPTAscope. Unlike
digital signals that typically are either high or low, analog signals can be high, low, or
any value in between. One of the most common types of sine waves that we can sense is
the sound wave. Sound waves permeate the air in three dimensions in the same manner
that ripples flow across a pond in two dimensions. A cross-section of the surface of this
pond would look something like the waveform in Figure 3-1.
Despite the fact that BASIC Stamps are digital by their nature, they can generate sine
waves. The interesting thing here is how they generate sine waves. The BASIC Stamp
must approximate the sine wave with a sequence of digital square waves that is later
filtered into a nice, clean sine wave. When you connect a piezoelectric speaker to a sine
wave you will hear a tone (provided the sine wave is oscillating at a frequency within the
audible range). This may sound confusing, but it will clear up as we work through the
next lesson. First, we need a little more background information.
The pulse train used to control servos is only one type of signal in a family of signals
called PWM. PWM stands for pulse width modulation. The servo pulse train is unique
in that it has a fixed “off-time”. Most PWM signals have variable off-time as well as
variable on-time. Consider the pulse train depicted in Figure 3-2.
Figure 3-1:
Typical sine wave – one cycle.
Figure 3-2:
PWM signal
train