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03/21/08 20:18
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 		 #152424 - Possibly noisy Relay/Switch Inputs
Hello Everybody,
Please help!
In this project,a AT89S52 has to detect separately 10 external relay contact closures happening at 10 remote places in highly noisy environment,intensive care units.
Instead of taking external connections directly to 8052,I thought of utilising the relay contacts to turn on 10 local LEDs focussed on 10 LDRs or using opto couplers or opto isolators like 4N35.The local power supply for the LEDs should be highish so that a local high value resistance is forced in series with the LEDs of the optos,which in turn should improve noise immunity.What is wrong in this approach?
http://www.8052.com/users/AsokRudra/MUSICAL.gif
Can somebody suggest a reference design interfacing 4N35 to AT89S52,because I have experience in detecting regular wavwe forms like Mains AC(Zero Crossing) but here I do not want to detect AC Mains or RF.Software debouncing has to be there but is this O.K.?
I shall appreciate every views.
With Best Regards
A.S.Rudra

List of 44 messages in thread
TopicAuthorDate
Possibly noisy Relay/Switch Inputs            01/01/70 00:00      
   Schmitt inverter            01/01/70 00:00      
      Thanks Steve but please note change            01/01/70 00:00      
         Steve's suggestion is certainly valid!            01/01/70 00:00      
            Thanks Richard            01/01/70 00:00      
               Do you really need the optoisolators?            01/01/70 00:00      
         Why Schmitt Gates            01/01/70 00:00      
            That is the purpose of Schmidt-triggers ...            01/01/70 00:00      
   This is how I would do it            01/01/70 00:00      
      I'd probably do that too, except ...            01/01/70 00:00      
      Thanks            01/01/70 00:00      
         The waters have been muddied ...            01/01/70 00:00      
            Thanks            01/01/70 00:00      
               Yes, it's clearer, but ...            01/01/70 00:00      
                  Priority Encoder Not a Good Idea            01/01/70 00:00      
                     Yes, highest priority input would mask others            01/01/70 00:00      
                     Welcome Sir Michael Karas            01/01/70 00:00      
                        Note Length & Cadence on One Timer            01/01/70 00:00      
         Noise            01/01/70 00:00      
            It's all analog            01/01/70 00:00      
   Another way to do this            01/01/70 00:00      
   how fast do you need to detect the contacts            01/01/70 00:00      
      Hello Erik,Hello Kai,            01/01/70 00:00      
         what are you describing?            01/01/70 00:00      
            actual distance test(ohmically)            01/01/70 00:00      
               please answer questions            01/01/70 00:00      
                  Part success            01/01/70 00:00      
                     In the last analysis, it is up to you            01/01/70 00:00      
                        Provocative            01/01/70 00:00      
                           totally irrelevant            01/01/70 00:00      
                     what 'common'            01/01/70 00:00      
                     Transformerless supply...            01/01/70 00:00      
                        Thanks            01/01/70 00:00      
                           I do not understand, parallelling switches            01/01/70 00:00      
                              Absolutely deadly dangerous!!!!            01/01/70 00:00      
                              parallelling switches            01/01/70 00:00      
                                 Sorry, but I see a contradiction...            01/01/70 00:00      
                                    shock? touching what?            01/01/70 00:00      
                                       Come on!            01/01/70 00:00      
                                          The standard to which we designed ...            01/01/70 00:00      
         I believe you may have missed the point            01/01/70 00:00      
   Current rating of relay?            01/01/70 00:00      
      not to nitpick, but            01/01/70 00:00      
         Thank you very much Erik            01/01/70 00:00      

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