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???
07/27/06 03:34
Modified:
  07/27/06 03:38
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 		 #121141 - I agree, but...
Responding to: ???'s previous message
Richard said:
Kai, I don't find the multi-key-closure problem very common with keypads.

You are totally right. In very most applications only one key is pressed at a time, where adding this diode stuff would definitely be over-engineering.

Nevertheless, X/Y matrices are not only used for single key applications but also for multi key applications. Think about polyphone playable electronic pianos or synthesizers, where up to ten keys can be pressed at a time. In these spplications it's very common to use these diode arrays to avoid "ghosting" and "masking".

Ok, maybe this issue is too sophisticated to be mentioned in a newbie's thread. Wasn't my intention to "muddle the water"...

Kai

List of 41 messages in thread
TopicAuthorDate
connecting a keypad . HOW?            01/01/70 00:00      
   Because...            01/01/70 00:00      
      How many times will this come up?            01/01/70 00:00      
         To be fair            01/01/70 00:00      
         Help him!            01/01/70 00:00      
            OK ... but just this once!            01/01/70 00:00      
   it's quite simple ... therein lies the beauty.            01/01/70 00:00      
      In minute detail            01/01/70 00:00      
         Credit goes to original author Michael Karas            01/01/70 00:00      
            Yes - Credit to Michael Karas            01/01/70 00:00      
      Diodes prevent \"ghosting\"            01/01/70 00:00      
         indeed, but rarely needed            01/01/70 00:00      
            Think of a piano, where each key counts...            01/01/70 00:00      
               How often do you intend to use multiple keys?            01/01/70 00:00      
                  There is the case of...            01/01/70 00:00      
                     True, but how often?            01/01/70 00:00      
                        Agreed            01/01/70 00:00      
                        general input            01/01/70 00:00      
                  I agree, but...            01/01/70 00:00      
      a small catch            01/01/70 00:00      
         In this case, the pullups were external            01/01/70 00:00      
            HUH????            01/01/70 00:00      
               Sorry, I should have said you must not ...            01/01/70 00:00      
                  just visualize            01/01/70 00:00      
                     It happens all the time ...            01/01/70 00:00      
                        current limits            01/01/70 00:00      
                           transistors open won't conduct            01/01/70 00:00      
                              Totally unsuited with push/pulls, unless...            01/01/70 00:00      
                                 This is true, which is why one should READ first            01/01/70 00:00      
                                    there is no reason, but 'linear thinking' (outputs            01/01/70 00:00      
                                       Some encoders "see" pretty high impedances            01/01/70 00:00      
                                          cruel and unusual            01/01/70 00:00      
                                       No!            01/01/70 00:00      
                                          OK, rephrase            01/01/70 00:00      
                                             Ah, sorry!            01/01/70 00:00      
                                    Benefit of additional pull-ups            01/01/70 00:00      
   Disappearing Original Post!            01/01/70 00:00      
      that is not all that is missing!            01/01/70 00:00      
         Bug            01/01/70 00:00      
            Bugs            01/01/70 00:00      
               OOps            01/01/70 00:00      

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