Email: Password: Remember Me | Create Account (Free)

Back to Subject List

Old thread has been locked -- no new posts accepted in this thread
???
06/07/08 09:04
Read: times


 		 #155575 - Input Protection
Hello,

I'm having doubts about the level of protection on switch inputs.
I have to read 24 switches with shift registers. The switches and board are in a closed housing and are connected to the board with wires up to 0.5metre.
The user can only touch the switches, nothing else.

Since there are 24 switch I don't want to overdo the input protection (RC filters, clamps, surpressors etc.).

My idea was to use pullups from +5V connected to the shiftregister inputs (obviously..) and a 100n cap to ground. The switch parallel to the capacitor.

Is this enough? I'm also a little worried about ESD.

Thanks in advance,

Peter



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      

Back to Subject List