Filtering noise from a wire

[Ioannis]

Then using shielded cables or wraping with copper foils like these may help on this: https://nl.aliexpress.com/item/10050...&mall_affr=pr3

But why bother with all this stuff? Did you have any reliability problems?

Ioannis

[Demon]

...But why bother with all this stuff? Did you have any reliability problems?

Ioannis

Nothing so far. I just like to be prepared for the worst case scenario if I can. But I'm not going to drive costs up 500% to protect from 0.0001% insane user conditions either.

My old scopes are acting up; switches and buttons causing noise on the screen; image is jumping like an old CRT. I'm not going to spend time figuring out if seemingly bad signals are real, or the result of faulty ancient equipment.

I'm waiting for a small scope that had a good review for testing switch debounce. I don't do any advanced scoping routines; I only need it to check 5V lines for noise and switch bounces.
Right now, I just don't know just how sensitive or hardy 5V circuits can really be.

What ordinary household items that a gamer might have on his desk that you would consider as the biggest causes of noise on circuits?

Electric kettle?
Large speaker?
Cell phone playing a movie?

I'm planning on setting up some tests to see just how much noise my circuit can pick up.

[Demon]

Then using shielded cables or wraping with copper foils like these may help on this...

I already have a lot of manual tasks required to assemble a single unit. I would probably get shielded wire; something like this.




I haven't searched for prices. I just took a pic of the first one I found.

But first I want to test to see exactly what I'm facing.

[Demon]

Case in point: these guys say a 10 meter wire is an antenna, but under 10 cm is nothing to be worried about (under normal circumstances).

https://www.eevblog.com/forum/beginn...54/#msg3863054

My longest wires might not even be longer than 10cm. I'm just starting the I/O Expander circuit (it's going to sit "somewhere" in the middle of a bunch of switches//buttons).

[richard]

what is the shortest switch activation period that you would expect to need to detect and how quickly do you need to respond ?
generally any key press under 50mS i would just ignore . for basically "static" switches 200 0r 300 mS would be more than adequate

why care about noise and debouncing if quick responses are not required

[Demon]

what is the shortest switch activation period that you would expect to need to detect and how quickly do you need to respond ?
generally any key press under 50mS i would just ignore . for basically "static" switches 200 0r 300 mS would be more than adequate

why care about noise and debouncing if quick responses are not required

The only issue I can think of is that I have rotary encoders. Nothing is preventing the user from turning 2 encoders at the same time while on auto-pilot.

There's also the possibility of someone flying with a co-pilot/navigator; that could mean the "possibility" of up to 4 encoders moving at the same time. I want to be ready for that.


My goal is to undercut the market by a wide margin. It's very possible someone with vested interests would try their best to find "bugs" with my product, and drag my name on flight sim groups.

For example: back in college during the late 70ies, Burroughs brought in a main-frame but we thought it sucked. So most a lot of computer students flooded the queues with duplicates of their jobs. The techs from Burroughs were not prepared; the machine failed, badly, and IBM came back. We didn't have vested interests, we were just goofballs, but we did crash the system.

Just look at this thing; couple of switches and 3 LEDs for $140CAD. That's insane. That's worth something like $20 at most. There's very few competition, so they pretty much do as they please.

I'm not the next Delorean, but I still expect resistant.

[richard]

I have rotary encoders. Nothing is preventing the user from turning 2 encoders at the same time while on auto-pilot.

rotary encoders are a completely different story to switches, you have virtually no chance of reading multiple re's via i/o extenders with any confidence that steps and direction changes won't be missed

[Ioannis]

Regarding the Rotary encoders Richard covered it 100%.

With shielded wires I am pretty sure you won't have any problems. Forget about R's and C's, just read two times the switch state and your are done with debounce.

As for long or short wires acting like antennas, well, the general statement "long wires act like antenna" is not quite right. It depends on the frequency we are talking about. For example, 10cm may seem very short, but this is an antenna for 750MHz and the 10m is an antenna for 7.5Mhz. So, which one may be a problem for you? It depends on what signal sources you have nearby, right?

Best way to deal with all frequencies is both cable shielding and metal case box wherever there is a possibility of interference.

But I think we are getting crazy on this...

Ioannis

[tumbleweed]

rotary encoders are a completely different story to switches, you have virtually no chance of reading multiple re's via i/o extenders with any confidence that steps and direction changes won't be missed

+1

If you're trying to use an IO expander to do that good luck!

[Demon]

what is the shortest switch activation period that you would expect to need to detect and how quickly do you need to respond ?
generally any key press under 50mS i would just ignore . for basically "static" switches 200 0r 300 mS would be more than adequate
...

I didn't have real world data yet. Here's the switch with the longest activation period mounted on a test PCB:

(similar to this switch, yellow circuit, about 10cm end to end)




5vdc with 10:1 probe
.1 volt / division
.2 ms / division




It takes 5 divisions for a press, so 1 millisecond end to end. The other switches take about 0.3 to 0.6 ms.

It has a blurry bounce of under 2 sub-divisions at the top (∼0.07ms), I saw at least one other press with a bounce twice as long (it was out of focus - I didn't save it).

I wasn't able to get any rising edges for some reason. I'm sure that has to do with the trigger settings, but I just don't know how to do that, yet.


This is what I get probed directly to an identical unconnected switch:




It took a lot less time to activate, under 0.5ms. I assume this is what you guys meant about traces acting as antennas.

[Demon]

At least now I have an idea of what sort of activation times and switch bounce that I'm facing. I really had no clue what sort of activation delays I was facing (never got this far in a project).

Now I need to test from a secondary PCB, out using wires (max 10cm) to a 1" x 1" switch PCB, and back to the secondary PCB.

That will give me actual data using the planned hardware.