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???
06/13/08 18:08
Modified:
  06/13/08 18:17
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 		 #155874 - Immunity against what?
Responding to: ???'s previous message
Peter said:
Will this improve the immunity of the input?

Immunity against what? Is there any noise you need to battle down?
Why are you so focused on the switch inputs only? What about the "latch", "clock" and "data" line? I guess you want to build something comparable to that:





Why not forming a 5 x 5 switch matrix, putting cera diodes and Schottky clamps to each line, connecting a tiny micro to it and transmitting the result to mainboard via RS485 bus (using the superb LT1785)? Use "vertical debouncing" in the micro and diodes in the matrix to prevent "ghosting".

Link discussing "vertical debouncing": http://www.8052.com/forum/read.phtml?id=76155

Link discussing "ghosting": http://www.dribin.org/dave/keyboard/one_html/


Kai

List of 42 messages in thread
TopicAuthorDate
Input Protection            01/01/70 00:00      
   I use a series resistor            01/01/70 00:00      
      I like clamps ...            01/01/70 00:00      
         I would not use a \'S\' chip            01/01/70 00:00      
            It's just an array of schottky diodes, Erik            01/01/70 00:00      
               Resistors and cap            01/01/70 00:00      
                  why the slowpoke            01/01/70 00:00      
                     the technology will still work in this case            01/01/70 00:00      
                        stupid boss            01/01/70 00:00      
                           ... or stupid Erik, maybe?            01/01/70 00:00      
                              I did NOT say "stupid engineer"            01/01/70 00:00      
                                 now, don't get me wrong here ...            01/01/70 00:00      
                                    a typical result of a stupid boss            01/01/70 00:00      
               well the 74S had me since ....            01/01/70 00:00      
                  Yes, it indicates the process technology            01/01/70 00:00      
                     HEF4021            01/01/70 00:00      
                        Anyhow the major setback using 40xx            01/01/70 00:00      
                           This is entirely wrong!            01/01/70 00:00      
                        No, not better, but different            01/01/70 00:00      
      Adding another cap            01/01/70 00:00      
         I do not think so, but it will wear the switch            01/01/70 00:00      
         Immunity against what?            01/01/70 00:00      
   No, just a business decision ...            01/01/70 00:00      
      Uhm...            01/01/70 00:00      
         all 40xx chips are based on the same technology ..            01/01/70 00:00      
         if the RC before the PISO doesn't do it ...            01/01/70 00:00      
            Values            01/01/70 00:00      
               I do not know why ...            01/01/70 00:00      
                  Values..            01/01/70 00:00      
                     like this            01/01/70 00:00      
                     Caps and RF immunity            01/01/70 00:00      
                        true - and not            01/01/70 00:00      
                           Expensive capacitors?            01/01/70 00:00      
            BALDERDASH            01/01/70 00:00      
               the PISO register is loaded only once ...            01/01/70 00:00      
                  I hav no desire to look up 40xx chips, but ..            01/01/70 00:00      
                     If there's nothing pressing ...            01/01/70 00:00      
                        Setup            01/01/70 00:00      
                           overdoing it            01/01/70 00:00      
                           That just might be adeuqate ...            01/01/70 00:00      
                              Switches            01/01/70 00:00      
                                 IF you choose the right rate ... and IF you check            01/01/70 00:00      

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