What is Switch bounce?

  • Thread starter Furion
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  • #1
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Ive been working on a new project for my studies but cant seem to get any info on 'switch bounce'
 

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  • #2
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It's the electrical noise made by metal coming together to form a circuit. It lasts maybe 40ms depending on the switch.

Google "switch debouncing circuit" and you'll get lots of examples.
 
  • #3
dlgoff
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If you are interested in cleaning up switch bounce (switch debounce), you can do it with a couple of nand gates.

debounce.gif


http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/setreset.html" [Broken]
 
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  • #4
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Is switch bouncing and de bouncing the same?because im not sure
 
  • #5
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Switch debounce and switch bounce are two different things.

Switch Bounce happens when you close a mechanical switch. When you close a switch it tends to literally bounce upon the metal contact which connects the circuit.

It's almost like dropping a basketball. The basketball will hit then ground (analogous to a closed switch) then bounce back up (analogous to a open switch) then bounce back down, then up, then down, etc... until it permanently stays on the ground (permanently closed).

Usually switches take a few microseconds to a few milliseconds to completely close. What this means in terms of digital logic is that as the switch physically bounces your logic can switch back and forth low-to-high-to-low-etc... until your switch settles down.

Switch Debounce is the process of getting rid of switch bounce. One solution to get rid of switch bounce is given above by dlgoff
 
  • #6
MATLABdude
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If you are doing microprocessor/controller work (e.g. with an externally-triggered interrupt), it's quite common practice to pause for a period of time (~20 ms or so) upon receiving an input in order to debounce a button / switch / relay.

A friend of mine nearly tore his hair out trying to fix an interrupt service routine where he'd forgotten to do this.
 
  • #7
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ohh I get it now make alot sense now thanks guys
 

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