28119 Parallax Inc, 28119 Datasheet - Page 48

• 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

The trigger is set with the blue arrow to the right of the Plot Area. As you move it up and
down you will see the signal move to the right and left. This is because the trigger event
lines up in the center of the screen. A trigger event happens when the input signal crosses
the trigger voltage on a rising edge. Let’s experiment!
√
√
√
√
Adjust the trigger level up and down to see the sine wave shift left or right.
Set the Trigger Edge switch to Falling , then experiment with the trigger level.
Set the Trigger Edge switch back to Rising. C hange the
argument; try several different frequencies. Note: you will have to download the
revised program into your BASIC Stamp or HomeWork Board each time.
For each frequency tested (at least five), adjust the trigger level to capture a nice
image of the sine wave. Make a mental note regarding the volume and pitch
differences.
Signal Problems? The piezo speaker signal shown below-left resembles the one you can
reasonably expect to see when using the piezo speaker included in the Understanding
Signals kit. If you are using a different speaker, your OPTAscope display might more
closely resemble the inductive speaker signal shown below-right. Some speakers look like
piezo speakers, but they use a coil (an inductive element) instead of a piezoelectric element
to vibrate the surface that generates sound. Because the properties of a coil are very
different from the properties of a piezoelectric element, the circuit is changed drastically, and
so is the signal that is measured and displayed by the OPTAscope.
Remedy: If you do not have a true piezoelectric speaker at your disposal, you can still view
the signal by removing the speaker from the circuit shown in Figure 3-3 and Figure 3-4.
When you re-run the program and capture the signal, it should more closely resemble the
piezo speaker signal example.
Piezoelectric Speaker signal example
Inductive Speaker signal example
FREQOUT
command’s
freq1