Question about LED matrix in general - how odes it work ???

Hi ... I had a look at this instructable www.instructables.com/id/LED-matrix-using-shift-registers/  and there is this picture with the schematic how to create the matrix www.instructables.com/files/deriv/FSW/VO3F/FHAVXXA0/FSWVO3FFHAVXXA0.MEDIUM.jpg

My question is how does it work, because I can't understand it. I'll give an example :

Imagine, you turn on 4 leds : LED1, LED8, LED57, LED64. And my question is, how are you going to turn OFF just ONE LED without affecting other LED's ???

When I'm looking at the schematic and I'm trying to TURN OFF LED 1 ... well if I turn off the ROW1 then I automatically switch off the LED8 as well...or NOT ???

Am I missing something or am I right ???

Thank you




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You're right, if you cut power to the row, all the LED's in that row will go dark.  What you're missing is that none of the LED's are ever steady-lit anyway, they're flashing in an 8ms cycling pattern. So even if it appears that 1 and 8 are both lit simultaneously, they're really not. They're just flashing alternately so quickly that it looks like they're both on. Same with any other LED in the row. When you "turn off" #1, you're really just telling it not to flash on when its turn in the 8ms cycle comes. The other LED's in the row can still be on or off for their turn in the cycle without affecting or being affected by the state of any other LED.
Boy, the workings of a matrix took me a long time to understand and you've just explained it in a paragraph.
I used to be a business systems analyst. Half of the job was translating complex technical concepts into easily digestible short explanations for non-technical end-users to understand. The other half was translating poorly conceived and articulated end-user requirements into language that developers could use to build systems that actually did what they were supposed to do.
I was very good at the job, but boy, did I hate it.
zholy (author)  RavingMadStudios7 years ago
Thank you for the answer. I was silently hoping that it's not flashing, but it is :(

In that case = do you know, what is the longest time for the ON-OFF-ON period that the human eye will not notice the flickering ??? You mentioned the 8ms which is fine ... but I'm doing quite few "math formulas" before flashing a LED som I know, it will be longer them 8ms.
I'm no expert on POV, but a quick Google scan leads me to believe that up to 50ms is probably the upper limit for where a human would begin to perceive a flicker. This doesn't account for any cool-down glow in the LED, though, which may buy you an extra ms or two. Or I could be totally wrong on either or both points. Any experts out there are welcome to correct me.