2012-11-23 16:41:39 +02:00
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Antorcha vs. Tornado feature comparison
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Number of LEDs 32 64
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Pixels 16 64
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LED pitch 8 mm 5 mm
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1 arc sec / pixel (1) 28 m 17 m
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1 arc sec / text (2) 70 m 90 m
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LED line length 25 cm 32 cm
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Total stick length 63 cm 53 cm (TBD)
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Outer radius ~ 90 cm ~ 80 cm (3)
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Visible width ~ 100 cm ~ 110 cm (3)
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Sweeps per second ~ 4, bidirectional ~ 3, unidirectional
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Sweep speed (avg.) ~ 8 m/s ~ 15 m/s (3)
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(1) http://en.wikipedia.org/wiki/Visual_acuity
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(2) 2 text lines, 1/12 display height
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(3) for chain length = 30 cm
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Weight
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------
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Al stick: 52.5 g / 52.7 cm = ~ 1 g/cm
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Chain: 44 g / 19 links = ~ 2.3 g/link
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305 mm / 21 links = 14.5 mm/link
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1.6 g/cm
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Attachment (screw, washers, nut): 2.3 g
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End cap: 1.54 g
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Cable: 1.74 g / 382 mm
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group of 3: ~ 0.14 g/cm
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LED PCB: 4.1 g
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CPU PCB: 4.5 g
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Not included in the weight calculation:
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- glue
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- adhesive tapes
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- isolation tapes
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- cable binders (if any)
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- heat-shrink tubing
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- cables/wires for inter-board connections
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Update rate
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-----------
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For square pixels we need one update every 5 mm. With the edge moving
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at 15 m/s, that's one update every 1/3000 s. If we assume that,
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including overhead, each 64 bit shift and latch takes about 100 clock
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cycles, the serial bus needs to run at no less than 300 kHz.
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sclk-1123.png shows the ~250 ns clock pulse generated by the current
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test firmware. CH2 (blue) is signal entering the first LED module,
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CH1 (yellow) is the signal exiting the last module. The absence of
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degradation in a 250 ns pulse suggests that we can go as fast as the
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MCU is able to.
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2012-12-19 19:11:42 +02:00
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Image size
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----------
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With a radius of 80 cm the circumference is roughly 5000 mm.
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In order to obtain square pixels at the outer radius, we therefore
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need 1000 lines per rotation, irrespective of speed. Each line
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consists of 64 pixels or 8 bytes of data. Therefore, the full disc
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needs roughly 8 kB of data while a quarter disc needs 2 kB.
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