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???
11/24/08 08:53
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 		 #160253 - EMI and PWM for brightness control
Responding to: ???'s previous message
Erik Malund said:

One issue, not to be ignored, is the tremendous amount of EMI a multiplexed sign generates.

Erik I noticed that EMI gets generated tremendously in non multiplexed displays because of PWM brightness control frequency on OE pins of the constant current driver ICs. When they turn on they consume alot of current suddenly generating EMI noise. So to reduce noise I turned the LED driver output off then clock the new data in then put them back on.
Does the brightness PWM frequency has an issue for EMI. I used 500Hz for my sign but didn't experiment with lower frequencies. I thought if I used 100Hz or lower PWM frequency one will notice the flicker if he is driving!
What PWM frequency will you choose?
Mahmood


List of 33 messages in thread
TopicAuthorDate
matrix LED logic            01/01/70 00:00      
   Did you see this thread?            01/01/70 00:00      
      About project            01/01/70 00:00      
         Start a new thread!            01/01/70 00:00      
   just curious            01/01/70 00:00      
      No homework this is.            01/01/70 00:00      
         matrix            01/01/70 00:00      
            the urban legend about matrix            01/01/70 00:00      
               Erik, do you...            01/01/70 00:00      
                  almost            01/01/70 00:00      
                     Thanks!            01/01/70 00:00      
                     EMI and PWM for brightness control            01/01/70 00:00      
                        EMI            01/01/70 00:00      
               OK, there are also other reasons...            01/01/70 00:00      
         so, no purpose at all            01/01/70 00:00      
         Why don't you search first, Ashwin?            01/01/70 00:00      
   LED/lights matrix            01/01/70 00:00      
      actually            01/01/70 00:00      
         I knew there is a better expression...            01/01/70 00:00      
            I understood you!            01/01/70 00:00      
               both are equally right ... it\'s retinal persitence            01/01/70 00:00      
                  It\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\'s strange...            01/01/70 00:00      
                     Number of \"\\\" is doubling, each time I modify!            01/01/70 00:00      
                        some kinda weird escape character            01/01/70 00:00      
   Sorry... (no message)            01/01/70 00:00      
   Which logic?            01/01/70 00:00      
      Lighting logic.            01/01/70 00:00      
         You could have said that earlier!            01/01/70 00:00      
   read \'Hurley\'            01/01/70 00:00      
      :(            01/01/70 00:00      
         Bad ISBN?            01/01/70 00:00      
            Amazon            01/01/70 00:00      
   Two-year-old thread revived!!            01/01/70 00:00      

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