max # of charlieplexed LEDs for POV to hold

Forum 2005-2010 (read only) Hardware Interfacing
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does anybody know the maximum number of LEDs you can drive using charlieplexing such that it can still look like any number of LEDs is on, because of persistence of vision?

i guess what i'm asking is: how fast can an atmega168 switch pin states? and what's the most time that can pass between flickers of an LED before your eye notices that it's flickering?

using 20 pins, you can drive 380 LEDs. could the arduino cycle through all of them fast enough?

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what's the most time that can pass between flickers of an LED before your eye notices that it's flickering

This depends on the individual's eyes but anything faster than 32 times a second should begin to look continuous. The TV system uses 50 (or 60) times a second.

So for 380 LEDs you need to access them 380 * 32 = 12160 times a second or at a rate of 12.16KHz. The Arduino has a 16MHz clock so yes it can display this many LEDs.

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Wasn't the orginal motion picture format fixed at 16 frames a second as that was the minimum speed in which most wouldn't notice a flicker? Maybe I'm too old and got that wrong :wink:

Lefty

4

12 frames per second for line animation (cinema cartoons)
24 frames per second for common cinema
25 frames per second for PAL video
29.95 fields per second for NTSC video

60 changes per second can still be seen by some people, and cause eye strain, which is why good monitors ensure refresh at 70 Hz, 85 Hz, even 120 Hz.

5

That's only half right the 16 frames per second was the rate at which it looked like continuous movement. To stop it flickering each frame of film was flashed on the screen three times giving a flicker rate of 16 * 3 = 48 times a second. So using less film.

That's also why TV uses interlacing, 25 frames a second but flicker rate of 50 flashes a second.

So next time you go to a cinema remember that half the time you will be sitting in the dark, two sixth of the time you will be watching repeats with only one sixth of the time watching something new.

So demand you pay only one sixth of the entrance fee. :wink:

6

So that's why my wife buys six times more DVDs then I care to watch :stuck_out_tongue:

Lefty