122-28176 Parallax Inc, 122-28176 Datasheet - Page 130

• 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

Figure 4-20 is screen shot of the fan's RPM when powered from Vin. The fan was
manually slowed by lightly touching it. Note the data obtained. The count obtained with
the retro-reflective switch is 134. With a sample time of 1000 ms (1 second), an RPM of
8,040 is calculated (134 x 60 seconds). With the 1 cycle/revolution encoder wheel,
counting the pulses for 1 second provides a value for revolutions per second. To obtain
revolutions per minute, the count is multiplied by 60.
In the BASIC Stamp code:
The count is multiplied by 60000 ms (60 seconds) and divided by
from StampPlot which is 1000 ms (1 second) by default. Finally, the result is divided by
the number of cycles per revolution, or 1 in this case. The digital trace, the green LED,
and the StampPlot indicator will toggle, or change states, during each loop iteration
(sample).
√
√
√
center. A typical reading is 8000 RPM, though this will vary with supply
voltage.
Lightly touch the front of the fan to vary speed, and monitor on StampPlot.
Monitor the RPM.
Skip these next two steps if you are using a BASIC Stamp HomeWork
Board!! Move the fan's red (+) lead to Vdd. The fan may need a 'jump start' by
manually spinning it. What is the RPM of the fan now? The fan used is a
brushless DC motor rated for 12 V with a dropout, or stall, voltage of 3.5 V. The
voltage supplied to it will affect its rotational speed.
Return the red lead of the fan to Vin or disconnect for now.
RPM = Count * 60 / #cycles per revolution
RPM = Opto_Count * (60000 / SP_Data) / CyclesPerRev
RPM = 134 * (60000 / 1000) / 1 = 8040 RPM
SP_Data
that was read