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???
02/07/10 14:10
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Msg Score: +1
 +1 Informative
#172956 - Never discharge a cap directly by a switch!
Responding to: ???'s previous message
Joel said:
@ everyone else - thankyou very much, I have tried another implementation of the switches on a separate piece of veroboard and changed the (what i thought to be brand new but cheap) switches for the ones I had ordered to be used on the final version. These work far more reliably!

The mistake is, that your switch directly discharges a cap without any current limiting! That burns down the contacts and results in a little, non-conducting oxid spot.

Always limit the current rushing through such a tiny switch to less than a few mA. So, don't discharge the cap directly, but via a resistor. Just put a resistor in series to the contacts, like shown in this example:



I think the evalboard from SILABS has 100k pullups? Then a current limiting resistor of 2k2 is adequate.

The current through such a switch should be more than 100µA, but less than 5mA, for reliable switching.

Kai Klaas

List of 13 messages in thread
TopicAuthorDate
Buttons - Hardware            01/01/70 00:00      
   do double check ....            01/01/70 00:00      
   Debouncing            01/01/70 00:00      
   Have you considered that it could simply be the "breadboard"            01/01/70 00:00      
      I (dis)agree            01/01/70 00:00      
      Relevance to pushbuttons            01/01/70 00:00      
         Consider the objective            01/01/70 00:00      
            Agreed            01/01/70 00:00      
               that's why there's so fluid a definition for "working"            01/01/70 00:00      
                  PCB's to match the contact arrangement on a "breadboard"            01/01/70 00:00      
                     Not exactly ...            01/01/70 00:00      
                        Solved:            01/01/70 00:00      
                           Never discharge a cap directly by a switch!            01/01/70 00:00      

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