122-28176 Parallax Inc, 122-28176 Datasheet - Page 156

• 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

As seen in Figure 5-8, a 100% drive, or duty cycle, is applied, and a sample of RPM is
taken. The %Duty and %RPM are plotted (and updated in the gauges). Next, a 95% duty
cycle is applied and RPM sampled.
Note that the digital trace shows the switching of the fan. Figure 5-8 is a close-up of the
switching. What happens to the HIGH time as the drive is decreased?
Does the fan produce a linear change in speed in relation to the drive? As we can clearly
see, it does not. However, this isn't the circuit's fault. It's a problem with the code in that
the fan is not provided a very clean duty cycle. Trying to switch the drive output on and
Figure 5-7 PWM Test with Manual Drive
Figure 5-8 PWM Drive Cycling