For my EE lab, our professor wants us to show switch bounce, and then eliminate it using hardware, and software debouncing.

However, I seem to be stuck on finding the switch bounce in the first place. Attached is a snapshot of my scope when the pushbutton switch is triggered. To my untrained eye I can't be sure if what I am seeing is actually even switch bounce, or simply transient LC-voltages. How do I tell the difference, and/or is it just possible that the pushbutton I used has almost no bounce?

enter image description here

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  • 3
    \$\begingroup\$ That's just LC ringing as you suspect, definitely not switch bounce. Try zooming out, switch bounce will be closer to a millisecond time frame. \$\endgroup\$
    – tomnexus
    Sep 7, 2017 at 1:52
  • 4
    \$\begingroup\$ Maybe your switch is too good. Try a different switch and also just try touching wires together if you want to see bad bouncing. \$\endgroup\$ Sep 7, 2017 at 2:41
  • \$\begingroup\$ Is it a spring loaded (toggle switch or push button) with hysteresis? These are kind that are undamped with bounce 0.5~10 ms for microswitches when closed. \$\endgroup\$ Sep 7, 2017 at 14:02
  • \$\begingroup\$ I also ran into this issue in school. Try to get the biggest, nastiest power switch you can find (perhaps from an old vehicle or power tool), and test that. \$\endgroup\$ Oct 23, 2019 at 3:15

1 Answer 1


Now you know what a series underdamped 2nd order effect looks like.

2nd order because there are at least 2 dominant reactive parts, L & C where the inductance and capacitance is probably the series wire length of your probe ground length and coaxial probe capacitance giving a sine wave around 30% of 40ns or 80MHz with a 10:1 probe.

Reduce the inductance length or adding series R to dampen the wave with Zc(f)=R would reduce the ringing.

But this as nothing to do with the question of course as I indicated in comments.


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