122-28176 Parallax Inc, 122-28176 Datasheet - Page 132

• Manufacturer Part Number: 122-28176
• Description: GUIDE STUDENT PROCESS CONTROL
• Manufacturer: Parallax Inc

Specifications of 122-28176

• Accessory Type: Manual
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: Propeller Education (PE) Kit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant

Note the period of the waveform. The time represented between each horizontal major
division, or dashed vertical line, is 2 ms. A complete cycle takes approximately 3.6
divisions.
Frequency is the inverse of period, f = 1/T.
More accurate readings are obtained by the software and displayed below the waveform –
133 Hz and 7.5 ms. How does the frequency compare to what the BASIC Stamp was
reading for a count of 1 second? Also note that the waveform does not go from HIGH to
LOW sharply. The rise and fall of the wave takes a finite amount of time (about 0.4 ms).
This is due to the time required for the encoder vanes to transition and the response of the
phototransistor.
Figure 4-21 Waveform of Phototransistor Output for 1 Cycle/Revolution Encoder
3.6 div x 2 ms/Div = 7.2 ms for the period of the wave (T).
f = 1/7.2 ms = 138 Hz, or the number of cycles per second (Hz).