What is switch bounce?

[Furion]

Ive been working on a new project for my studies but can't seem to get any info on 'switch bounce'

 

[Antiphon]

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.

 

[dlgoff]

If you are interested in cleaning up switch bounce (switch debounce), you can do it with a couple of nand gates.

http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/setreset.html"

 

[Furion]

Is switch bouncing and de bouncing the same?because I am not sure

 

[Feldoh]

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

 

[MATLABdude]

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.

 

[Furion]

ohh I get it now make a lot sense now thanks guys