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Capacitor Question

Discussion in 'Electronic Basics' started by [email protected], Feb 9, 2006.

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  1. Pooh Bear

    Pooh Bear Guest

    Funny then that every data sheet or app note I've ever seen for a 78 series regulator
    *explicitly* states that no output cap is required for stability.

    The advantage of an output cap here is enhanced transient response.

    I just noticed you're from an educational institution ! No damn surprise there. Time you
    got out of your ivory tower and had to deal with the *real world*.

    Some of the most fuckwittedly idiotic things I've heard in my entire life have come out
    of the mouths of so-called 'pro-fess-ors' !

    Graham
     
  2. Guest

    Guest Guest

    : wrote:

    : < snip elegant discourse of no practical value >

    : Also note that every batch of ICs may perform slightly differently. Making something
    : that works on the bench doesn't guarantee every product using that design will behave
    : identically.

    Therein lies your problem. You don't see the value of
    understanding what you work with. You simply follow "rules of thumb," or
    "ground rules," and make no effort to understand what is going on around
    you. The fact that your "ground rules" work for your specific
    application does nothing to demonstrate how knowledgeable you are.
    In this specific example, your filtering of the input signal to the
    regulator does not guarantee that the regulator will remain stable.
    Give me enough time and I will find a scenario that breaks it.

    Since you want to bring numbers of successful designs into this,
    out of the HUNDREDS OF MILLIONS of the ICs with my regulators on them, I
    am not aware of a single RMA relating to those regulators. Does that, in
    and of itself, mean that I am correct here? No, but at least I can
    present my ideas elegantly (in your own words) and describe the workings
    of the circuits involved without (initially) resorting to name calling.
    What I was describing wasn't a "clever trick," but a simple mathematical
    truth about a simple analog circuit. Your assertion that understanding
    what is happening around you is of no value is just plain sad.

    And you call me blind? My participation in this thread is over.
    I have better things to do than argue with you over simple details about
    simple circuits. Perhaps, one day, you will see the value of
    understanding the circuits that you work with, but I'm certainly not
    going to be able to convince you of that over the internet.

    Best of Luck,

    Joe
     
  3. Pooh Bear

    Pooh Bear Guest

    I don't have a problem. I solved the problem that happened before I came along and fixed
    it.

    I understand perfectly thank you. I use rather more theoretical analysis than most
    engineers I know. I don't use that as a substitute for practical experience though. I
    combine the two.

    You haven't a clue. I was writing circuit models using Mathcad back in 1989.

    I don't care about demonstrating that. Engineering is about making stuff that *works* - not
    arguing to the board of directors when the line is backed up that ' it shouldn't have
    happened ' according to some hare-brained theory.

    You just said that the input *doesn't* need local decoupling !

    Your university directory lists you as a student.

    Where are these hundreds of millions of ICs ? They obviously aren't 78XXs.

    Maybe one day you'll understand the value of making stuff that has to work in the real
    world rather than in academia.

    Graham
     
  4. Guest

    Guest Guest

    : wrote:

    : I just noticed you're from an educational institution ! No damn surprise there. Time you
    : got out of your ivory tower and had to deal with the *real world*.

    : Some of the most fuckwittedly idiotic things I've heard in my entire life have come out
    : of the mouths of so-called 'pro-fess-ors' !

    : Graham

    Last, short comment: I am not a professor, but, do attend a
    University, as you so cleverly deduced from my .utexas.edu email address
    (boy, that must've been tough!) I earned my engineering degrees a long
    time ago, however, from a different university.

    Since you like spending time checking me out, point your browser
    to www.uspto.gov, instead. The patents that you're likely to find
    aren't all mine (by some coincidence, there's someone else with a
    similar name that has a lot more patents than I do.)

    Why did my comments bother you so much that you actually spent
    time "investigating" me? I could care less about you, although I DO see
    why you hide behind an alias (there ARE sickos like you out there that go
    around looking people's personal information up over a disagreement over
    voltage regulators!)

    Successful innovation requires a thorough knowledge and
    understanding of what you are working with. Perhaps, unlike you, I'm not
    in this to slap circuits together using "ground rules" that someone else
    told you. I'm not denying that that's how a lot of engineering is done,
    but engineering needs thinkers like me, as well as followers like you.
    Perhaps I'm wrong and you are a world-class innovator, but your attitude
    doesn't show that.

    Granted, this thread began about how to choose capacitors for a
    7805, (hardly a problem requiring innovation,) but in my experience, your
    method of desinging by "rules of thumb" has gotten people around me in
    more trouble than my method of thoroughly understanding what I am working
    with has gotten me.

    Joe
     
  5. Chris

    Chris Guest

    Hi, John (and all). I believe the signal voltage output from the
    transmission varies proportionately to the battery voltage, which may
    change with motor RPM. In that case, it might be easier for the OP to
    use an external reference voltage which is a voltage divider of the
    battery voltage, rather than using the on-board reference voltage on
    the PIC. Or, if the OP wants to go back to the comparator model, he
    could just use a voltage divider from the power supply as the reference
    to be divided down by the resistor divider string.

    Chris
     
  6. Pooh Bear

    Pooh Bear Guest

    Oh Lord !

    Battery voltages don't mysteriously vary with motor rpm !

    Battery voltage varies with state of charge and applied load/charge current. A
    small battery driven from a motor driven generator will indeed vary its voltage
    according to the charge current ( which may vary with speed ) but not in any
    direct useful relationship.
    It seems he was already using a 7805 regulator to drive his sensor.

    If it was indeed a potentiometer sensor ( as guessed by some posters but never
    mentioned by the OP ) the varying output in any given gear is likely due to
    'uncertainty' on the input shaft of the pot since a gear selection doesn't
    provide a precise mechanical input.

    Graham
     
  7. I agree.
     
  8. There is little mystery about it. On many motorcycles, the alternator
    regulation is very poor, with thew alternator not keeping up at low
    engine RPM, and overcharging the battery at full RPM. Many don't even
    have a regulator, but just rely on a fair match between alternator
    current capability and motorcycle electrical system load.
    No. He said the sensor is already connected to the electrical system,
    and he is just tapping into the output signal. It is a pot that
    senses gear shifter position and is probably part of a voltage divider
    across the electrical supply.
     
  9. Pooh Bear

    Pooh Bear Guest

    I fully appreciate the above which you have explained excellently.

    It seems however that certain ppl are mistakenly associating a change in battery
    voltage with a direct relationship to motor rpm - which there *isn't*.

    So where did the 7805 ever come into the equation ? I got the impression that the
    sensor's input was 5V.
    I guessed that much, from your posts as much as anything. The 'uncertainty' about the
    output voltage would clearly seem to be a result of the mechnical input not being
    precise.
    Once again I thought it was driven from 5V. Why mention a 7805 otherwise ? Of course
    the OP seemed to be terminally incapable of describing his setup accurately.

    Graham
     
  10. The O.P. has stated that his electrical system voltage rises as engine
    RPM rises. I take him at his word, on this. This does not imply
    proportionality, only variation in a particular direction.
    You are being a bit too literal.

    (snip)
    The O.P copied a commercial circuit that has a microprocessor powered
    from a 5 volt regulator, and so, has an A/D converter that uses the 5
    volt regulated voltage as its A/D reference voltage. It is the
    mismatch between the pot supply and the A/D supply that is causing
    trouble, in my opinion.
    There will certainly be some of that, but it doesn't explain the wrong
    gear position indicator flashing when the engine is revved up.
    That may be a big part of his problem. He really doesn't understand
    the workings of the key pieces of his puzzle (the pot and the way it
    is powered, and the A/D converter and how it is powered and
    referenced). Rather than give him a complete course, we have sort of
    been hanging around, discussing various details, waiting for the
    various lights to come on in his mind, so he will either figure some
    of it out, or ask useful questions. There are no answers so useless
    as the answers to unasked questions. We have to be patient and wait
    for the questions to be asked, if we are to have any hope that the
    answers will not be misunderstood, or worse, ignored. We have lots of
    understanding and answers that the O.P. may not be ready to hear, yet.

    He just wants to get this thing finished and working, so he can ride.
    I am interested in his electronics education, and know that
    frustration and desire are good motivators for learning. If we had
    redesigned his circuit immediately on his first post, so he could have
    built a perfectly working unit, without understanding anything, he
    would be doing something else, now, instead of building up all this
    new understanding. So far, we have bumped into voltage dividers, A/D
    converters, microprocessor programming, regulators and the electrical
    systems on motorcycles. How much better is that than just having a
    shift indicator that merely works, perfectly? I am willing to bet
    that his new knowledge will change his life for the better more than
    the shift indicator, eventually will.

    Why are you taking part in this discussion? That is not sarcasm, but
    a sincere question.
     
  11. Pooh Bear

    Pooh Bear Guest

    I take your point. In effect I'm being 'terribly precise' because I note that those without
    a formal science background are prone to 'jumping to conclusions'. But I'll bet there's a
    *lag* involved in that relationship too

    I saw a link to a motorbike site that had some comparators driving leds. Is that the one
    you mean ?

    Without looking in greater detail at the comparator arrangement I'd hesitate to comment.

    I admire your tenacity.

    I've done this with the likes of Boki too and got a result. The thing is - Boki will
    actually respond sensibly when you ask a direct question. The OP here simply seems to go
    off at a tangent when asked for detail.

    Seems to me like a classic case of the '**** you' attitude. If you can't spoon-feed me the
    answer then screw you. The way 'education' seems to be going.
    You'll note that I gave a detailed answer to the OP's original question, having had to make
    an assumption that he knew what 'smoothing' was about when he mentioned it. Since the
    original post was a complete blind alley and I had simply wasted my time I was curious to
    see why the OP then chose to respond with such bile to someone making an effort to provide
    some knowledge.

    I'll bet that his guy is an utter waster frankly. His attitude ( and arrogant ignorance of
    technology ) speaks volumes.

    Graham
     
  12. Doesn't that depend on the internal resistance of his battery? It may
    be a tiny thing (and he kick starts the bike).
    This is the microprocessor design he is trying to copy:
    http://www.sportdevices.com/gearindicator/schematics.htm

    He has also built a multi comparator version, so we may be talking
    about two different circuits.
    He may be having too many conversations with too many people at the
    same time, and getting them confused.
    I haven't gotten that impression, but we probably see people differently.
    Evidently, he didn't see in your response, what you intended it to
    contain. Communication from this distance has problems.
    He cannot waste anything he doesn't have.
     
  13. Pooh Bear

    Pooh Bear Guest

    Internal resistance certainly plays a part.

    Strange thing is - he talked about a *car* originally. I know my car's battery voltage sticks
    nicely at 13.8V ( typical on-charge voltage ) after a few minutes drive.

    Ok. Hadn't seen that one before. Sadly doesn't show the 'gear sensor' itself.

    It seems so. I have indeed seen the comparator version.

    I suspect the underlying problem is the same though.

    I also suspect he went to a new circuit to 'fix the problem' not realising that underlying cause.


    Maybe so. I reckon I'm right though. I get the distinct impression that this is one 'cocky' guy
    who's happy to accept he knows little but plans to 'blag it' anyway.

    I certainly wouldn't want anyone like that on any team of mine. Likely to have a net negative
    influence.

    Given that he didn't apparently understand what his own question asked I guess so !

    I use the term in the vernacular sense. As in 'a waste of space'.

    Graham
     
  14. Pooh Bear wrote:
    (snip)
    Think back. Was there a period in your life (a long time ago, I'll
    grant) that this description might have applied to you?
     
  15. Pooh Bear

    Pooh Bear Guest

    No.

    I might have seemed cocky to some but I *never* needed to 'blag it'. Strange as it may seem to
    today's kids I actually enjoyed learning and delighted in educating myself about technology.

    I *still* enjoy learning too.

    I've always felt confident about my work because it's backed up by a strong knowledge of the
    fundamentals.

    Graham
     
  16. Perhaps I have guess wrong on the meaning of "to blag". It sounded
    like something I might have done in my youth.
    But we are talking about teaching.
    And you are able to be humble about it, too. ;-)
     
  17. True Love, he said "True Love", Max.

    -Valerie, "The Princess Bride"

    Happy Valentines day.
     
  18. Bob Myers

    Bob Myers Guest

    "He distinctly said 'to blave.' And, as we all know, "to blave" means "to
    bluff." So you're probably playing cards, and he cheated --"

    - Miracle Max, "The Princess Bride"


    Bob M.
     
  19. Hangglider

    Hangglider Guest

    Wow. That took a long time to read all the way though this post. I am
    a novice at electronics and I'm excited just to get a circuit to work
    the way I want it to. I posted a while back about a blown sub woofer
    and was delighted by the quick replies and helpful advice I received
    from this group and I was actually able to fix the problem! (damn if
    that didn't make me feel like a million bucks!)

    Please fellas, keep in mind that this google group is titled
    "sci.electronics.basics" (I emphasize BASICS). I appreciate that you
    guys are experts in the field but please don't scare away the folks who
    truly just want to get a little help as they get started with their
    projects and questions. Maybe their is another Google group out their
    for "philosophical" discussions about electronics theory, but this is
    just for us "simple folk".

    Please cool off boys.

    Thanks,
    Joe
     
  20. Each person who posts here does it for their own reasons. Some of the
    side trips get pretty useless, but some of them lead to pay dirt.
     
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