122-28176 Parallax Inc, 122-28176 Datasheet - Page 159

• 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

Chapter 5: High Current Drive and PWM Control · Page 149
Figure 5-9 PWM Drive using the PWM Command
Figure 5-9 is a sample plot of the drive versus the RPM. The linearity and control is
much better than the prior result, though the lower voltage limit of the fan is soon
reached.
The PWM command controls the duty cycle for the given amount of time (up to 255 ms).
As mentioned, the
argument range is 0 to 255. Since our drive is 0% to 100%, we
Duty
must apply a transfer function to arrive at an appropriate value for the PWM instruction:
x 255 / 100.
Duty
Figure 5-10 is a capture of the waveform at the drive pin for a 50% duty cycle. While the
BASIC Stamp does not produce as clean a duty cycle waveform as we have discussed,
the average of the high time is still 50% as noted by the average voltage produced (2.34 is
approximately 50% of 5 V). Also note the frequency of the waveform – 112 kHz. This
very fast switching of levels produces the desired duty cycle.