Welcome to the Parallax Discussion Forums, sign-up to participate.
The BASIC Stamp is toggling an I/O pin, that is, switching between HIGH and LOW. Using
the cursors, we can measure how long the signal is high. It will show that the high signal
lasts for 10 ms, just as you programmed the BASIC Stamp to do.
√ Under the Cursors tab, set the Cursor Settings switch to Vertical Bars.
√ Drag the bars to either side of a high pulse.
√ In the Auto Measurements box, read the delta (Δ) value in the Time column. It
should be around 10 ms.
√ Under the Trigger tab, set the Trigger Edge switch to Falling. Notice the signal shifts
to the left. Now the oscilloscope is triggering on the falling edge of the input
√ Move the trigger voltage above 5 V, out of the range of the signal. Notice the
rolling effect. The OPTAscope is looking for a trigger event but does not find
one because you have the Trigger Mode switch set to Auto. This causes the
OPTAscope to automatically trigger even though the input signal never causes a
valid trigger event.