Slew rate of the Prop 1 pin

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  • kwinnkwinn Posts: 8,036
    edited February 11 Vote Up0Vote Down
    Heater. wrote: »
    Toby,

    I think you are right. In that perfect world the source impedance matches the transmission lines characteristic impedance which matches the input impedance at the receiving end. That way your signal arrives intact and there are no horrible reflections to worry about.

    But wait, as you say, the signal level at the far end is only 50% of what the transmitter is putting out. That means it may not meet the logic level requirements of the receiver. Not so perfect anymore.

    I suspect that for the short distances that a logic signal is expected to travel that is not the the thing to do. Reflections are not an issue. There you want low output impedance and high input impedance. And hence can have a large fan out.

    I guess this is why we have dedicated transceiver chips and bus drivers for such like.

    I wish I could find the SPICE simulation of a transmission line I made years ago. You know, a lot of series inductors with capacitors in parallel. It was a nice demonstration of what goes on in a transmission line. Unrealistically perfect of course.

    One thing you can do to increase the signal level at the far end is to place a small capacitor between the terminating resistor and ground rather than connecting it directly. This is something that was done on high speed computer busses that used 220/330 ohm or similar value resistors between +5V and ground.
    In science there is no authority. There is only experiment.
    Life is unpredictable. Eat dessert first.
  • kwinn wrote: »
    One thing you can do to increase the signal level at the far end is to place a small capacitor between the terminating resistor and ground rather than connecting it directly. This is something that was done on high speed computer busses that used 220/330 ohm or similar value resistors between +5V and ground.

    Very cool, thank you for the tip.

    Any com port in a storm.
    Floating point numbers will be our downfall; count on it.
    Imagine a world without hypothetical situations.
  • mikeologist,

    Love the SVHS players story. One of mine is a bit similar...

    Back in 1980 something the Marconi Company had designed a neat power supply for the military. It was for use in aircraft equipment testing so it output 115V AC at 400Hz.

    Problem was they would build these, calibrate them, and ship them. Except by the time they got to the customer the output voltage was not what it should be.

    This was getting serious. These things are expensive, as all military gear is. A design review and/or redesign was on the cards. A whole project in itself.

    As a green horn electronics trainee in the company that didn't know anything much I happened to noticed that if I built and calibrated one of these supplies on the bench it's output would change as I put the lid on it's enclosure.

    Hmmm...thinks... eventually I tracked the problem down to a diode somewhere in the regulation circuitry that was a bit light sensitive. Taping over that stabilized everything nicely.

    The actual fix of course was to specify a different, light insensitive, diode.




    Now I'm curious... why the need to measure the slew rate?
  • mikeologistmikeologist Posts: 337
    edited February 12 Vote Up0Vote Down
    Light sensitive diode, that's awesome.

    I had the cross-talk issue and that lead me to read about transmission lines and how the work with MCUs. I fixed the problem with the termination or bounce-filter or whichever purpose the cap and resistor does. I've received plenty of good advise here for you and others as well on other approaches to investigate. However, the issue here isn't a gaffer's tape fix that doesn't really solve the issue. Here I desire to understand the nature of what is going on rather than simply applying a fix.

    I have a ton of different silabs MCUs, as well as many others from other manufacturers. For those I have tracked down all that esoteric info where it isn't provided.

    Now comes the next question, why should I care that much if a fix is available?
    Are you familiar with Tuvan throat singing? Youtube Video

    I'm envisioning some as of yet unseen scenario wherein I have several ICs with different slew rates finding some manner of complimentary frequencies and generating massively unexpected results based on the generation of harmonic overtones.
    As for the possibility of this happening, have you ever seen what happens when all three phases of three phase power are harmonically balanced instead of offset to 120?

    I'm really trying to dig deep into every part of the propeller theory. I believe this chip has loads of potential.
    Any com port in a storm.
    Floating point numbers will be our downfall; count on it.
    Imagine a world without hypothetical situations.
  • Strangely enough I used to know a young Finnish guy that could do Tuvan throat singing. He was a singer in a heavy metal band and used to open their gigs with a spot of solo Tuvan throat singing. It really grabbed the audience's attention.

    When it comes to high speed / high slew rate interconnects you might like to read these:
    http://www.analog.com/media/en/training-seminars/tutorials/MT-097.pdf
    http://www.ni.com/white-paper/3854/en/
    http://www.ti.com/lit/an/spraak6/spraak6.pdf

    If you want theory and mathematics there are things like this:
    https://mycourses.aalto.fi/pluginfile.php/143620/mod_folder/content/0/material_12_10_transmlines.pdf?forcedownload=1
    https://s2629002012.files.wordpress.com/2012/11/huitransmissionlines.pdf

    Sorry, no bright ideas about Tuvan throat singing chip interconnects :(








  • Heater. wrote: »
    Strangely enough I used to know a young Finnish guy that could do Tuvan throat singing. He was a singer in a heavy metal band and used to open their gigs with a spot of solo Tuvan throat singing. It really grabbed the audience's attention.

    When it comes to high speed / high slew rate interconnects you might like to read these:
    http://www.analog.com/media/en/training-seminars/tutorials/MT-097.pdf
    http://www.ni.com/white-paper/3854/en/
    http://www.ti.com/lit/an/spraak6/spraak6.pdf

    If you want theory and mathematics there are things like this:
    https://mycourses.aalto.fi/pluginfile.php/143620/mod_folder/content/0/material_12_10_transmlines.pdf?forcedownload=1
    https://s2629002012.files.wordpress.com/2012/11/huitransmissionlines.pdf

    Sorry, no bright ideas about Tuvan throat singing chip interconnects :(

    Finnish heavy metal and Tuvan throat singing, now that's a combo I had never considered :smile:
    So you've heard them in person. It's quite a show the first time when you don't know what to expect.

    Sweet, I will add these to the ever expanding reading list. At least my tablet doesn't get heavier when I add a new book.
    Thank You

    Also have this weird idea floating about wherein 2 gates with carefully chosen slew rates could be used to generate 3 or more meaningful outputs simultaneously by use of intentionally generated harmonics. Same as above, but in reverse. I'm sure I've made some mistakes in this, but it reminds me of the odd issues that Edison and later Bell had with harmonic telegraphy. I believe they filtered out these odd harmonics and intentionally selected tuning forks that generated discordance instead of harmony. In an ironic twist, I pretty sure the concept was later embraced and enhanced by Bellcore in their work on DSL. Were you in telephony at the time? I think you said you worked for the big Canadian telephony company.
    Then the follow-up question: if 2 gets you 3, can 3 get you 5?
    I'm probably missing one or more fundamental concepts here, but it still makes for an interesting day to think about it.
    Any com port in a storm.
    Floating point numbers will be our downfall; count on it.
    Imagine a world without hypothetical situations.
  • Here a better sample of random harmonics: Past life melodies
    I did this in my high school choir, the entire song is a warm-up for the last 80 seconds, so I've skipped most of the song in the link.
    In the sheet music the author explains the theory from a singers standpoint. As best I can remember over the gap:
    Every singer lands on a low B flat, no exceptions or it doesn't work. Discordance can destroy the entire effect.
    This note is chosen because it's the note most likely to cause the mask to vibrate sympathetically.
    About 20% of the choir maintains mask shape and tone, the other 80% are supposed to start to vary the internal shape of their mouths in an interesting pattern MMM-MOO-AARRR-EEEEE-UOUO-OOMM, rinse repeat in about 30 to 40 second cycles, two per breath. For the most dramatic effect the variants are supposed to be randomly staggered.
    Any com port in a storm.
    Floating point numbers will be our downfall; count on it.
    Imagine a world without hypothetical situations.
  • Sorry, but I am still having difficulties with the notion that it couldn't be sorted out with gaffer tape, when clearly WD40 would be on no use. It must be one or the other!
  • Toby,

    It's easy.

    If it moves when it should not, apply tape.

    If it does not move when it should, apply WD40.

    If it's really intransigent, hit it hard with a blunt object.

    As a last resort, cycle the power.

    I think that covers most common faults.




  • Sorry, but I am still having difficulties with the notion that it couldn't be sorted out with gaffer tape, when clearly WD40 would be on no use. It must be one or the other!

    Think this problem came down to dollars vs sense, but I do keep a can of dehydrant right next to the 3 in 1. The duct tape, well that's everywhere!
    Any com port in a storm.
    Floating point numbers will be our downfall; count on it.
    Imagine a world without hypothetical situations.
  • Heater. wrote: »
    Toby,

    It's easy.

    If it moves when it should not, apply tape.

    If it does not move when it should, apply WD40.

    If it's really intransigent, hit it hard with a blunt object.

    As a last resort, cycle the power.

    I think that covers most common faults.

    Reminds me of my weather rock instructions:
    If rock is wet it is raining
    If rock is white it is snowing
    If rock is gone it is windy
    Any com port in a storm.
    Floating point numbers will be our downfall; count on it.
    Imagine a world without hypothetical situations.
  • Peter JakackiPeter Jakacki Posts: 7,836
    edited February 12 Vote Up0Vote Down
    Heater. wrote: »
    Toby,

    It's easy.

    If it moves when it should not, apply tape.

    If it does not move when it should, apply WD40.

    If it's really intransigent, hit it hard with a blunt object.

    As a last resort, cycle the power.

    I think that covers most common faults.

    LOL ;)
    Except I have a French friend that instead of gaffer tape uses silicone glue for anything that should not move. You can depend upon him to always have fresh cartridges and a gun loaded and ready :)

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