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I have bought single push buttons in India for 1 rupee a piece, that's a penny or so. They are seemingly very basic (you can see them around here other question). I might follow up here with more details. I also bought a supposedly 100 MHz digital scope HTC brand. It being the first time I have a digital scope in single mode, I tried to visualize the button bouncing.

Strange thing is I could not. I was able to fry a chip's input by a series capacitor from button tied to high to input pin, pushing the button a few times to often. But I never once saw a single bounce. Compare this with my desperate attempts of building various de-bouncing circuits with various buttons I had before, I am flabbergasted. Should I worship the buttons for magically being bounce-free or should I mistrust my scope? The scope did show me 100-nanosecond sized events, so I can't really find evidence of fault with it. But I have no experience with what tricks cheap digital scopes might play on us.

The mentioning of capacitor in series has nothing to do with this issue. I am simply working with both at the same time. I provided the link above if it is of interest, but it's not really related. Here am simply measuring the output of the button tied high. Nothing special. I only put the capacitor into the schematics below to de-confuse the issue and show how far removed from the button the capacitor is, and yes, that it is a death hazard to the input of the gate following it.

schematic

simulate this circuit – Schematic created using CircuitLab

I will follow up on this with my bounce counter to verify. But wanted to ask if bounce-free buttons have ever been seen in the wild? So you don't go off on high-tech DOD-classified area 51 unicorn buttons, this is how naive they look:

enter image description here

enter image description here

Here is a related question and answers, but it doesn't address my question how it can be that I do not detect a single bounce event with dozens of actuations under the scrutiny of the scope on the activation edge.

UPDATE: I now built my bounce counter (a 74LS161 with 4 LEDs) to count button actuations. If any multi-counts occur we have a bounce. I found that on push there was no bounce. Ever. With this button. Bounces were seen rarely on release. One such event I capture in the following picture.

enter image description here

More than one counter skip were not observed (or too rare to notice). Extremely high quality button apparently. I will get another boat-load of those. Trying to find out the manufacturer. Will also test another 10 random from the batch. And will look for other kinds of this manufacturer, would be great to have one that closes a circuit in both positions to use with an S-R latch contraption to get the last rare possibility of bounces resolved.

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    \$\begingroup\$ Why did you put a series capacitor between the button and the "chip" input? That isn't the way to do it. You probably kicked the input above Vcc and destroyed it. Prior to destruction you would possibly have had some clamping by the input protection diode and this may have debounced the switch. Instead try a test circuit with a pull-up on the input and have the switch pull to ground. That will be realistic at least. \$\endgroup\$
    – Transistor
    Commented Aug 25, 2022 at 8:32
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    \$\begingroup\$ @GuntherSchadow: It might be better if you provide a circuit diagram showing how you have things connected. \$\endgroup\$
    – JRE
    Commented Aug 25, 2022 at 8:52
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    \$\begingroup\$ The scope won't do debouncing - as you say, that wouldn't be a good thing. What winny was trying to say was that debounce circuits aren't common when using microcontrollers because it is simpler to do the debouncing in software. \$\endgroup\$
    – JRE
    Commented Aug 25, 2022 at 10:03
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    \$\begingroup\$ No, not the observation part but the actual usage in the end. Will it be used in a system with a microcontroller? \$\endgroup\$
    – winny
    Commented Aug 25, 2022 at 11:31
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    \$\begingroup\$ @SimonFitch I thought I indicated death hazard and death with the universal symbol for the same, no? \$\endgroup\$ Commented Aug 25, 2022 at 14:52

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Should I worship the buttons for magically being bounce-free or should I mistrust my scope? The scope did show me 100-nanosecond sized events, so I can't really find evidence of fault with it.

On a fast-sweep oscilloscope capture, you might see only ONE of many bounces.

One would likely set up the 'scope controls like this to see switch bounce:

  • Set trigger to NORMAL rather than AUTO trigger, so that the display is frozen when the button's state is static. SINGLE trigger is also acceptable. This way, you only get a display when button is pressed or released.
  • Set trigger LEVEL to about half-of-DC supply...if you switch +5V to GND, set to +2.5V
  • Set trigger COUPLING to DC rather than AC.
  • Set the 'scope input channel you're triggering on to DC-coupled rather than AC-coupled.
  • Set horizontal time scale to about 1ms/div, so a complete screen-width is about 10ms.

If you set horizontal scale too-fast, you may see only one bounce edge, and miss others. Shown below is a button-release 'scope capture, from a tactile push switch looking very much like the OP's photo. A 47k pull-up resistor went to a +5V DC supply: scope trace of button release showing bounce


I noted that a few pushes and a few releases were apparently bounce-free. The capture shown was roughly typical. Button pushes had a higher percentage of bounce-free edges than button releases.
Note that the full-span width is 3.2ms.

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  • \$\begingroup\$ That’s exactly how to capture bounce. Also, bouncing tends to wait for the demo day. Switches wear out, and those cheap ones wear out especially fast. After a couple thousand actuations they are like a completely different part (and usually they become very crappy). \$\endgroup\$ Commented Aug 25, 2022 at 14:03
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    \$\begingroup\$ Thanks for walking me through the settings. I followed them and so I am now quite sure that both my scope and my switches are in order. Sure after thousands of actuations they may wear out. But I worry about that another year. \$\endgroup\$ Commented Aug 25, 2022 at 14:26

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