Difference: BlingBlingFunktionsweiseEn (3 vs. 4)

Revision 42016-03-28 - PeterSchmid

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Mode of Operation
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Dank dem Stroboskopeffekt entsteht für das Auge den Eindruck, als ob das Bild stehen würde. Die LEDs müssen dafür im richtigen Takt ein- und ausgeschaltet werden. Für ein Radumdrehung braucht es etwa 750 ms bei 10 km/h, bei 100 km/h sind das 75 ms (angenommener Radumfang bei einem Rennvelo ist 2.1 m). Der Abstand zwischen zwei LEDs beträgt 5.12 mm, im gleichen Abstand werden die LEDs geschaltet, das ergibt bei Maximalgeschwindigkeit eine Einschaltdauer der LED von 270 us (d.h. weniger als 0.3 Tausendstelsekunde). In dieser Zeit müssen die 16 LEDs auf der Vorderseite und die 16 LEDs auf der Rückseite geschaltet werden.
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Thanks to the stroboscopic effect, the impression arises, that the image is motionless. The LEDs have to be turned on and off in time with the wheel rotation. One full wheel rotation takes about 750 ms at 10 km/h velocity, at 100 km/h it takes only 75 ms (supposed circumference is about 2.1 m for a 28" wheel). The radial distance between two LEDs is 2" (5.12 mm), the supposed tangential distance is the same for the same tangential and radial resolution. At maximum velocity the switch on period for a LED is 270 us. There have to be 96 LEDs (32 LEDs times 3 colors) switched in this period. That means there is only 3 us time for single LED.

circumference for 28" race wheel
C = 2.105 m

vmax = 100 km/h = 27.8 m/s
tmin = C ⁄ vmax = 75.8 ms

Tangential distance between 2 LEDs
dradial = dtangential = 5.12 mm

rLED = 0.23 m
CLED = 2 • π • rLED = 1.445 m

tswitch = tmin ⁄ (CLED ⁄ rLED) = 269 μs

 
Stroboscopic Effect
The stroboscopic effect is a visual phenomenon caused by aliasing that occurs when continuous motion is represented by a series of short or instantaneous samples. It occurs when the view of a moving object is represented by a series of short samples as distinct from a continuous view, and the moving object is in rotational or other cyclic motion at a rate close to the sampling rate. It also accounts for the "wagon-wheel effect", so-called because in video or film, spoked wheels on horse-drawn wagons sometimes appear to be turning backwards.
 
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