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???
07/26/06 13:54
Modified:
  07/26/06 13:55
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 		 #121074 - Diodes prevent \"ghosting\"
Responding to: ???'s previous message
Richard said:
Remember, if you write a zero to a row, it will appear in a column only if a switch is closed. If it appears in more than one row, then you've probably struck more than one key. I recommend you guard against that, as it will produce confusing "sneak paths" which give false readings.

These false readings, also called "ghosting", can be avoided by using additional diodes, like it's shown here, for instance:

http://www.dribin.org/dave/keyboard/one_html/

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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