October 05, 2008

hi-tech stop sign; santa clara, CA

interesting visual effect here ... due to persistence of vision, when
you stand and look at the sign in person you perceive all the LEDs
hitting at the same time ... the camera shows it as a bottom-to-top
progression ... not the reason i shot it, but so very fun.

may have to go back and shoot a night one.


Blogger birdhead said...

What's probably going on here is they've got a microcontroller that doesn't have 8 direct ports out, so they use a shift register to control the LEDs. The controller has a serial bus to the shift register, so it pushes out 1,1,1,etc. to turn the lights on, pauses, then pushes 0,0,0,etc. It takes 8 clock cycles to turn the LEDs on, and 8 to turn them off. The clock is fast enough that your eye doesn't catch it, but slow enough that the camera does.

Monday, October 06, 2008 8:12:00 PM  

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