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Chapter 04
Developing a Utility Library for the Propeller PCB
Page 13
D and its importance
D is the time required by the propeller to rotate one degree.
After solving the hypothetical questions, which assumes that D is known. The fact is that D is NOT known, it needs to be calculated. Suppose a propeller is rotating, how to determine the RPM? How to find D?
The previous questions just showed the importance of D.
Lets assume: Once D is calculated, the patterns can be displayed.
But another problem is that D is NOT a constant. A motor rotates the propeller. The user can control the voltage of motor to change its RPM. The user may reduce the RPM if there are too many vibrations. The user may like to increase the RPM to get more Persistence (to get a clear image on display). But, as the RPM of propeller is changed, D value also changes.
When someone looks at his/her shadow in water; and the water is disturbed, the shadow is also disturbed. Similarly, if some pattern is being displayed on POVD and RPM is changed the pattern is disturbed, this is undesirable. If somehow D is calculated dynamically, this problem is solved. Not only the value of D is required, but it is important to find it dynamically.
Chapter 7 Interfacing the Index Sensor explains how to solve this problem
By the way, in this POV display, D is calculated dynamically. If the motor RPM is changed in the range of 800 to 2400 the pattern is not disturbed. The following video illustrates this.
Displaying and Varying RPM limits on the Arduino based DIY Persistence of Vision Display Clock
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