B3F-4055 switch bounce

[Demon]

Received my $2 scope and tested one of my switches.

Does this result seem possible?




I expected some flutter, but this switch has no bounce. Either the switch performs much better than I anticipated, or this scope device is garbage.

[Ioannis]

I suppose you have only a switch and a resistor, right?

Either you got a perfect switch or the scope is slow enough with low memory depth.

I will do a similar test. Maybe you have to use 5ms/div or lower?

Ioannis

[richard]

i would not expect to see any "bouncing" at 50mS per div , @ 0.5mS/div you are more likely to see something

[Demon]

Only the switch, says Omron underneath. Zero resistors or capacitors.

I wanted to do a baseline so I had something to compare any debounce circuitry.

I'm gonna test some other switch types and omron clones.

[Ioannis]

I suppose you have to add the whole circuit. Omron is a good company but in any case, mechanical switch always have a small time of bouncing.

Ioannis

[Demon]

i would not expect to see any "bouncing" at 50mS per div , @ 0.5mS/div you are more likely to see something

I went back and redid the tests. Here's the falling edge of a SR-25 rotary switch on a BK Precision 1560 at 1ms:



(Let me know if there's a better setting for the scope. I just went with trial and error.)


And the rising and falling edges on the DSO-TC3 at 1ms:





It's not even remotely close to similar. I should have started testing with the BK; its buttons aren't making the screen jump around.

The Tektronix 466 was giving mismatched readings; giving a jagged trace, then curves, then just dropping on/off. It would need a serious cleaning, which I can't afford. And that wouldn't repair worn switches and pots, they'd need to be replaced. Let alone if there's fried circuits in there. I figure the old owner got rid of it for a reason.


Here's a pic of the SR25 switch. That wiper seems to bounce a lot as it moves out of one position and into another.

[Ioannis]

Well we expected the BK screenshot response. That is what a good switch bounce should be!

The Fnirsi I guess is either for the recycle bin or has some settings to smooth out the ripple so much that looks like a perfect rect wave.

The SR25 switch, depending on their oxidation state, since the contacts are very much exposed, is normal to have such a behaviour.

Ioannis

[Demon]

...The Fnirsi I guess is either for the recycle bin or has some settings to smooth out the ripple so much that looks like a perfect rect wave....

It's a toy to help teach electronics, nothing more. I'm starting my first return to AliExpress, along with those 3 DMMs that I tried out. I'll see how that goes.

EDIT: I was wrong about this device (next post).

...The SR25 switch, depending on their oxidation state, since the contacts are very much exposed, is normal to have such a behaviour.

Ioannis

This one is brand new though; straight from the manufacturer 2 months ago.

Turns out this was caused by me touching the metal shaft. As soon as I installed a knob, that erratic bounce has mostly gone away. There's still a slight bounce, but nothing so drastic.

It did show to me though that the chinesium scope is useless to analyse signals adequately.

[Ioannis]

If any actuator has metalic case, it is wise that case to be earthed. Metals tend to work like touch sensors or antennas if not properly earthed.

Ioannis

[Demon]

Turns out it helps if you use a device properly, who knew.

The edge can be controlled by the little icon at top left, and SINGLE mode stops updating once triggered (you have to press RUN to reset).

I accelerated the sweep rate, which helped detect some noise but at least it's matching the old scope now.




It does have a few seriously good qualities: it's small, easy to deploy, and not overly complicated. Granted, the screen is small, but at least it can serve as a confirmation of what I see on the BK 1560.

One slight drawback, it seems to lag after a few minutes. It's as if internal storage has a problem managing all the data it accumulates. It gets progressively slower, it's very evident when you press the buttons (the beep gets progressively slower in response).

Still, it's not a bad buy. I'm definitely getting one with a larger display screen later.

[Demon]

If any actuator has metalic case, it is wise that case to be earthed. Metals tend to work like touch sensors or antennas if not properly earthed.

Ioannis

The MR0102 toggle on the right has a support bracket with 4 pins. I can easily ground those.

The SR25 SP4T on the left has no such pins.




I suppose I could pass an eyelet connector over the shaft and fix with a nut and then ground the wire to the PCB mounting screws. I have about 1cm of room under the knob; more than plenty for the plastic enclosure.

That will be a concern on the RV17 rotary pot; the shaft is short and I don't have much thread space. :/

[Ioannis]

Maybe you can solder a wire on the SR25 metals. With patience I have to say...

Ioannis

[Demon]

I'm thinking of leaving open pads under the 2 crimps on both sides.

[Demon]

Maybe you can solder a wire on the SR25 metals. With patience I have to say...

Ioannis

I was shopping for laser engravers to etch white text on black PLA and saw that a machine to cut thin steel plate would be expensive.

I started thinking of glueing aluminium foil onto a thin plastic sheet, and then using the mini-CNC to mill the sheet to fit inside the enclosure cover. That way the metal switches would touch against the aluminium foil, and then ground that. It might act as a EMI shield inwards and outwards, maybe.

Anything thin and conductive could do the job, not just aluminium. It's just a matter of finding something that is workable, and inexpensive, aluminium foil is just so readily available here.


EDIT: I can't believe I didn't think of this right away. Single-sided copper-clad PCBs are readily available and can be milled to fit. I just need to find a cheap and reliable source (haven't checked yet).

[Demon]

I just saw copper mesh on Amazon, which got me thinking about going even much simpler. Just snaking a bare copper wire along the inside of the enclosure cover. I only have to touch the metal surface on the switches.

No machining, just hot glue and a connector at the end to bring it back to GND. Cheap and easy implemented. I just won't be getting any structural strength or shielding. :/

[Ioannis]

In general the SR25 and other alike pots etc, are supposed to be mounted on a metal surface which is grounded by default.

Maybe you can do the same. On the plastic enclosure have a thin aluminum face, cut in you CNC. Then you may do also lettering and drop silkscreen ink in the engraving. The latter will require thicker metal sheet though.

Ioannis

[Demon]

I'm leaning more towards snaking a bare wire along the inside of the enclosure cover. It'll do the job of grounding all the metal components, and it's cheap and without serious machine labour.

I've also been thinking a lot about how to get lettering on the front. My first idea was engraving acrylic sheets and backlighting with LEDs, but I've already got a LOT on my plate as it is.

So I found out you can etch into PLA without any special hardware or material. An diode laser engraver "should' do the job (I need to do more research).

It's a matter of testing settings. This guy is using a 30 watt machine at 20%; that's only 6 watts. I'm looking at 20 watt machines, since 10 watts doesn't leave a wide margin.

[Ioannis]

And how exactly are the lettering painted white on the black PLA?

This looks very nice.

Ioannis

[Demon]

Something about removing pigment and exposing the original material. Apparently PLA is white with added dies.

There's other explanations on the web like "overheated air bubbles get trapped in the material thus changing the colour", but this one seems to be the most accepted. It's possible that they're both correct to some degree. I just wouldn't bet my life on the scientific reason just yet. As long as it works, that's all I care.

I always thought they used a two-layer material; black exterior over base white. A laser would remove the black layer exposing the white base. Something like what I bought to try out on the mini-CNC:

https://www.amazon.ca/Engraving-Doub...7QT93LN9/?th=1

I haven't tried them yet. They're a bit expensive, but the white base is semi-transparent; you can shine LEDs through them and create text with backlight.

[Ioannis]

Impressive!

Ioannis