By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th

Would this improve the quality of signal to a CNC machine?

(If it used USB for data transfer)

All Topics | Latest Posts

Search for:  in Thread Title in  
Emgee27/02/2021 11:13:06
1988 forum posts
250 photos
Posted by James Hall 3 on 27/02/2021 10:13:25:

Martin Kyte: you may well agree with Andrew Johnston on this one but you would, with respect, both still bee wrong.

Bit of a sting there James however it's read.

Emgee

Martin Kyte27/02/2021 11:35:13
avatar
2313 forum posts
38 photos
Posted by James Hall 3 on 27/02/2021 10:13:25:

Martin Kyte: you may well agree with Andrew Johnston on this one but you would, with respect, both still bee wrong.

This really is DigComms 101 - kids' stuff. To say that a digital signal is really an analogue one because it is carried over an analogue channel is as ridiculous as saying that an analogue signal is really a piece of wire because the piece of wire carries the electrons. I've tried to think up an illustrative analogy with the difference between the meaning of word and a dumb spell-checker for you further amusement - but it proved to be too contrived.

Any time varying current is analog. I suppose you would agree that a sine wave is an analog signal. Well a pulse train is a series of sine waves of different frequencies. Do the Fourier transform. For USB the data is encoded and decoded as digital on the analog carrier as I said which is what makes it a digital communications channel but the connection is analog. It is splitting hairs but that's the way it is.

regards Martin

Tom Sheppard27/02/2021 12:06:54
27 forum posts

A digital signal is an analogue signal with only two or three levels. That is why it is called a digital signal. (Yes, if zero is a level, and it is, then digital signals can have three levels, but they are still digital signals.)

Andrew Johnston27/02/2021 14:58:52
avatar
5976 forum posts
668 photos
Posted by James Hall 3 on 27/02/2021 10:13:25:

This really is DigComms 101 - kids' stuff.

I must have skipped that class. You're not the first new member to wade in guns blazing and telling people that they're idiots and I don't suppose you'll be the last. Generally it reflects badly on the new poster and while some quieten down many disappear without trace.

As a doctor I'd advise you to visit your GP, as breathing cutting oil fumes seems to have affected some cognitive abilities.

Andrew

Andrew Johnston27/02/2021 15:17:33
avatar
5976 forum posts
668 photos
Posted by Martin Kyte on 27/02/2021 11:35:13:

Any time varying current is analog. I suppose you would agree that a sine wave is an analog signal.

Precisely, which is why I asked about FSK, as in it's simplest form it consists of bursts of two sine waves, but is considered as being a digital signal. smile

The definitions of digital signals above are fine as far as they go, but are limited. The question of noise is an interesting one, first analysed by Shannon and Hartley. But consider a GPS signal which can be at least an order of magnitude below the background noise level, but can still be decoded. Speaking of decoding, a comparator deciding whether a signal is high or low is an example of hard decision decoding. Newer algorithms, such as Viterbi decoders, use soft decision decoding based on the reliability of each code. Logic levels at the gate level are normally described as above a given level is 1 and below another given level is 0. Zero is normally included in the lower range rather than as a discrete logic value. The precise voltage is unimportant provided it is above, or below, the specified levels. There is normally a voltage range between the levels where the signal is neither 1 nor 0. Of course more than two levels can be used, although the only common example is a third state of high impedance aka tri-state logic.

Andrew

Mike Poole27/02/2021 17:08:52
avatar
Moderator
2940 forum posts
70 photos

A well designed cable and made with reasonable quality materials does not cost very much. It is unlikely to be the cheapest you can find but it will be very affordable. Many data systems can correct errors or retry so poor performance can be compensated for, only when performance drops to a very low level will failure be signaled. Design is the first hurdle because poor design cannot be compensated for by using high quality materials but a good design can be ruined with poor materials or workmanship.

Mike

Tom Sheppard27/02/2021 17:09:59
27 forum posts

Or RS-232.

James Hall 327/02/2021 18:27:46
37 forum posts
8 photos

Martin Kyte wrote:

" Any time varying current is analog. I suppose you would agree that a sine wave is an analog signal. Well a pulse train is a series of sine waves of different frequencies. Do the Fourier transform. For USB the data is encoded and decoded as digital on the analog carrier as I said which is what makes it a digital communications channel but the connection is analog. It is splitting hairs but that's the way it is."

That's more sensible and describes the mechanism - but actually supports the necessary differentiation between the digital and analogue. It really is not splitting hairs as an appreciation of the difference between signal, channel, carrier and their 'layering' is essential to any understanding of digital (or any other form of) communications.

I apologise if I may have overreacted to seeing incorrect statements regarding digital signals but teaching digcomms to half a generation of undergraduates (most of whom have achieved good degrees and gone on to successful careers in R&D and industry) has made me particularly sensitive to any misconceptions of this sort.

Cabinet Enforcer27/02/2021 19:27:02
101 forum posts
3 photos
Posted by SillyOldDuffer on 26/02/2021 21:58:19:

Maybe hifi systems use usb cables as ordinary audio connectors and aren't digital at all. A convenient bodge, but prone to analogue defects, that might be reduced by a decent cable.

What's needed is a good dose of double-blind testing. For some strange reason it's never done...

Dave

No, they are intended for digital use, Ian really has linked to a three and a half grand USB cable.

Take a look at some of the utterly mind bending drivel in the second of his links, my favourite bit was this " This innovative layout allows the two signal wires to run parallel, compared to the standard twisted-pair configuration, shortening the signal path and drastically increasing transfer speeds"

The thing I really don't understand about audiophiles is why none of them have twigged onto the most obvious way of improving the sound experience, that being reception fidelity interoception. The simple and straightforward application of a pair of underpants to the head supplemented with correct tuned length wood and graphite frequency modifiers in the nasal cavity can take the listening experience from the sublime to the ridiculous in one fell swoop.

Stuart Bridger27/02/2021 21:00:23
517 forum posts
29 photos

I will put my hands up and admit that I am a hi-fi fan. My investment in Hi-Fi way exceeds the value of my workshop.

That said the digital part of the system uses standard Ethernet patch leads costing a few pounds. The argument used for the esoteric USB and network cables is reducing the noise transmission from the digital to analogue domain rather than the quality of the signal itself. I don't buy it and I agree that there is a lot of snake oil in the industry. None of purchases have been made without auditioning first.

The comments about made about no difference between bell wire and a quality speaker cable clearly come from those who have never heard the latter. I will happily admit to spending £40/m on cables and it was the best investment I made, with a dramatic improvement.

I have had friends round (before lockdown) who like music but don't have a quality playback system and they have been blown away by the sound quality.

Anthony Kendall28/02/2021 10:05:46
102 forum posts
Posted by Stuart Bridger on 27/02/2021 21:00:23:

snip...
The comments about made about no difference between bell wire and a quality speaker cable clearly come from those who have never heard the latter. I will happily admit to spending £40/m on cables and it was the best investment I made, with a dramatic improvement.
Snip

Maybe the poster was being just a little flippant but using thicker low-loss cables than thin bell wire can improve the listening experience. Paying £40/m is your choice and if you like the result, that's fine you can spend your cash on what you like without comment from me. Similarly, I can have an opinion for me, and for me, I think it is very poor value for money - and yes, I have tested it all out.

Posted by James Hall 3 on 27/02/2021 18:27:46:

Snip....
I apologise if I may have overreacted to seeing incorrect statements regarding digital signals but teaching digcomms to half a generation of undergraduates (most of whom have achieved good degrees and gone on to successful careers in R&D and industry) has made me particularly sensitive to any misconceptions of this sort.

I think some might interpret this as willy-waving.

Anthony Kendall28/02/2021 10:40:40
102 forum posts
Posted by Cabinet Enforcer on 27/02/2021 19:27:02:
Snip...
The thing I really don't understand about audiophiles is why none of them have twigged onto the most obvious way of improving the sound experience, that being reception fidelity interoception. The simple and straightforward application of a pair of underpants to the head supplemented with correct tuned length wood and graphite frequency modifiers in the nasal cavity can take the listening experience from the sublime to the ridiculous in one fell swoop.

Difficult - I think Mr. Edmund Blackadder has the patent.

John Haine28/02/2021 10:43:32
3784 forum posts
220 photos

Just going back to the original (tongue in cheek) question, I think it's rare for CNC machines to use USB to carry any signals - there are USB connected motion controllers but it seems to be generally reckoned that Ethernet is better. Lathe does have a USB connection from the PC to the breakout board but it is entirely to supply +5V and carries no data. There are high-speed pulse signals from the controller to the steppers but they are at 40 volt 2.5 amp levels.

SillyOldDuffer28/02/2021 10:53:39
Moderator
7042 forum posts
1549 photos
Posted by Anthony Kendall on 28/02/2021 10:05:46:
Posted by Stuart Bridger on 27/02/2021 21:00:23:

...

...

Posted by James Hall 3 on 27/02/2021 18:27:46:

Snip....
I apologise if I may have overreacted to seeing incorrect statements regarding digital signals but teaching digcomms to half a generation of undergraduates (most of whom have achieved good degrees and gone on to successful careers in R&D and industry) has made me particularly sensitive to any misconceptions of this sort.

I think some might interpret this as willy-waving.

Now then, let's not have pistols at dawn over the difference between Analogue and Digital Signals! This is a jokey thread about highly dubious USB cables, not an advanced class in telecommunications theory.

I know what James meant, and I know what Andrew meant and feel the difference is semantic. A slight twist in what's understood by 'analogue' has led to unecessary trouble at t-mill.

For what it's worth (not much!), I suggest a digital signal is a digitally modulated analogue carrier. The carrier, another word we could start a row about, could be light, radio waves, or on/off keying of a DC voltage. In my book good old Audio Shift Frequency Keyed radioteletype once ubiquitous on short-wave radio is a digital signal, but it's sent by alternating two audio tones and applying them to modulate an RF carrier, also analogue. The receiver is analogue up to the point the two tones are converted into binary HIGH/LOW, at which point the signal is pure digital.

I'd be amazed if anyone disagreed that the charactistic of analogue modulation is information represented by continually varying values, whereas digital is information represented by a stream of HIGH/LOW transitions, however HIGH and LOW are defined.

Dave

Andrew Johnston28/02/2021 11:29:58
avatar
5976 forum posts
668 photos
Posted by James Hall 3 on 27/02/2021 18:27:46:

..........teaching digcomms to half a generation of undergraduates.......

That's interesting. At which university did you teach?

Andrew

Andrew Johnston28/02/2021 11:49:13
avatar
5976 forum posts
668 photos
Posted by SillyOldDuffer on 28/02/2021 10:53:39:
I'd be amazed if anyone disagreed that the charactistic of analogue modulation is information represented by continually varying values, whereas digital is information represented by a stream of HIGH/LOW transitions, however HIGH and LOW are defined.

Prepare to be amazed! What about Gaussian pulse shaping? Analogue filter theory used to shape a digital pulse stream.

Another topic to mull over is QAM - quadrature amplitude modulation. It's amplitude modulation but mostly used for digital information, eg, digital terrestial TV in the UK. Each symbol can have many levels, so more than 1 bit can be transmitted in one symbol, 64 and 256 are common values, as the constellation is normally square. Where's the dividing line between continuous modulation and modulation of many discrete steps?

Andrew

James Hall 328/02/2021 11:53:18
37 forum posts
8 photos

Andrew: Cambridge.

James Hall 328/02/2021 12:04:25
37 forum posts
8 photos

SillyOldDuffer:

" I think some might interpret this as willy-waving."

Well, I've had more graceful responses to an apology

The Interweb is packed with nonsense, advice and 'howtos' posted by idiots who have no idea of which they speak so in my experience it's always a very good idea to check provenance before accepting anything too readily. I merely pointed out that I do actually know what I'm talking about - why should you apparently have some sort of problem with that?

Andrew Johnston28/02/2021 12:12:59
avatar
5976 forum posts
668 photos
Posted by James Hall 3 on 28/02/2021 11:53:18:

Andrew: Cambridge.

When were you there? I was at CUED from 1980 to 1986, but don't recall your name.

Andrew

Hopper28/02/2021 12:17:19
avatar
5404 forum posts
131 photos
Posted by Andrew Johnston on 28/02/2021 11:49:13:
Posted by SillyOldDuffer on 28/02/2021 10:53:39:
I'd be amazed if anyone disagreed that the charactistic of analogue modulation is information represented by continually varying values, whereas digital is information represented by a stream of HIGH/LOW transitions, however HIGH and LOW are defined.

Prepare to be amazed!

I'd be more amazed if anybody on this forum ever agreed with anybody else!

But I am constantly amazed at the breadth and depth of knowledge on this forum.

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
ChesterUK
JD Metals
Eccentric July 5 2018
Warco
cowells
emcomachinetools
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest