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How inaccurate is a 555 or 7555 REALLY?

Discussion in 'Electronic Design' started by WildIrish, Dec 2, 2006.

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  1. Guest

    Unless you find yourself a crystal oven and keep it at a steady 70C, or
    build yourself a proper temperature controller around a Peltier
    junction - the one I published managed
    +/-0.001C, but would have been a tight fit in a 3/4 inch package.
    Sometimes. I don't get too worried about such allegations until they
    put down their own numbers.
    Not always true. Inductors have a nasty tendency to shift inductance as
    the DC current through the coil changes, even if you keep the
    temperature constant (whichcan be a little difficult if you are
    changing the heat dissipated in the coil).
     
  2. Guest

    It isn't the whole story, like most manufacturer's specifications.
    If he isn't in a production environment, how many capacitors does he
    have to buy to find one that drifts the right way to the right extent?
    Bearing in mind that capacitors from a single batch are usualy a lot
    more similar that parts from successive batches.

    Selecting parts is a mugs games.
    10MHz crystals are a lot better than 32768Hz crystals. My Farnell
    catalogue is back i Nijmegen, which made it difficult to be
    quantitative.
    Mainly because it is temperature controlled by your wrist.
    That was a typo - it should have been 0.001% or +/-5ppm. I used to
    worry about that sort of error - now I just try and cross-check.
    Everybody makes an error like that about once every 30 minutes when
    sober ...
    Once it has warmed up

    Which has an operator to provide AFC via a slow PLL
    Regular FM radios have a PLL to provide AFC, lacking an operator
    prepared to act as a dumb servo ina slow loop.
    I do, you don't. Pity about that.
     
  3. Jim Thompson

    Jim Thompson Guest

    On Sun, 03 Dec 2006 06:44:33 GMT, Robert Baer

    [snip]
    And once you choose an R-C, what does those irregularities have to do
    with stability?

    Most of the temperature variation in a 555 timer would come from the
    delay time through the comparators to the output.
    Probably not.
    Agreed.

    ...Jim Thompson
     
  4. mri_bob

    mri_bob Guest

    To quote you: "Try to understand the technology you pontificate about
    before you claim to be getting real"
    I do, you don't. Pity about that.



    i guess i will have to turn in my engineering diploma then. i have run
    into clowns on newsgroups before who attacked other peoples ideas just so
    they could tell their own stories about how much they know, it's nothing
    new.

    i was attempting to help a novice learn why it would be difficult but
    maybe not impossible to do it with a 555 if temperature was tightly
    controlled but that a microcomputer circuit would be better. bill has his
    own agenda which is different from mine. i'm finished with this topic.
    people who need to end their posts with insults have nothing to offer to
    me.

    -bob
     
  5. WildIrish

    WildIrish Guest

    Thanks for all the great and useful data and information everyone,
    I really started a firestorm of argument on this topic. I'm happy
    to switch to the dividing circuits, but i'm stuck with using AA's... is
    there
    any packages that anyone can think of which will divide at that
    low of voltage that doesn't have minimum frequency limitations
    yet still pretty small?

    Programmable solutions are acceptable, however I've gone
    crosseyed looking at datasheets that all show minium 3v with
    min Fout of xxxkHz instead of low hz ratings.

    ~Brendan

    PS to Phil - not everyone is as worldly as you, I humbly described
    myself
    as a novice so as not to apear rude, or to get answers that are
    rediculously
    over my head. Everyone has to learn by asking questions, that is the
    notion
    behind discussion forums.... not for certain individuals to show off
    how
    'amazing' they are. 'Novice' is is a relative term... My engineering
    degree is
    still novice compared to a NASA engineer. I never said 'no experience'
    so
    your statement of "Then it is time to realise that YOU are not up to
    the task"
    is rude and uncalled for.... thanks for the positivity.
     
  6. Robert Baer

    Robert Baer Guest

    But making an oven to keep temperature within 3C is not difficult, so
    that part is not "totally impractical in the real world".
     
  7. Robert Baer

    Robert Baer Guest

    ? "Nijmegen" ?
    *What* is that?
     
  8. Robert Baer

    Robert Baer Guest

    That ratio is temperature sensitive...
     
  9. Jim Thompson

    Jim Thompson Guest

    What "ratio" is that?

    ...Jim Thompson
     
  10. mri_bob

    mri_bob Guest

    in passing, i would like to address bill's ridiculous claim that a digital
    watch was only accurate to better than a minute or two a day because it
    was temperature regulated by the wearer's wrist. ridiculous nonsense that
    shows an ignorance of thermodynamics and of the stability of digital
    timepieces in general. How do you suppose the hundreds of millions of
    cheap digital wall clocks are thermally regulated?

    -bob
     
  11. Are you actually trying to generate a sine wave output?


    Best regards,
    Spehro Pefhany
     
  12. A town in the Netherlands, whose roots lie in the Novio Magnus
    military camp by the ancient Romans. Also the home of the Katholieke
    Universiteit where my wife went to the medical school.

    Regards,
    Mikko
     
  13. Guest

    I wouldn't bother making the effort. Diploma's don't count for much.
    The IEEE admitted me as member 26 years ago without any evidence of any
    academic training in engineering (I do have a Ph.D. in Physical
    Chemistry) on the basis of a declaration from one of the IEEE members
    at EMI Central Research that I knew what I was talking about. I'd
    gotten two patents i the three years I'd worked there, so they may have
    had an exaggerated idea of my competence.
    And it does tend to stop people sounding off about stuff they don't
    know enough about.
    Based on a fairly wearing month or so back in 1974 trying to do the
    same job for an over-optimistic boss. We ended up getting fairly close
    with an emitter-coupled multi-vibrator, but the temperature dependence
    of the Early effect was bad enough that even that circuit didn't make
    it.
    Then you are condemned out of your own mouth.

    Your second message in the thread - message 6 in the lst ends " let's
    get real, huh? "
    which is the kind of discourtesy I repay in kind. My own idea of my
    attitude on this news group is "polite until provoked" but John Larkin
    does keep on finding insults in my posts that I could have sworn
    weren't there when I composed them (and don't look much like insults to
    me when I reread them). Phil Allison would blame this on autism, but he
    blames a lot of stuff on autism. He's not an expert psychologist,
    unlike my wife's academic colleagues (who won't use me as a test
    subject any more, because I know too much).
     
  14. Robert Baer

    Robert Baer Guest

    The ratio of the ersistor calues in the (comparitor) divider.
     
  15. Robert Baer

    Robert Baer Guest

    ** And *nobody* thought of using cascode?
     
  16. Jim Thompson

    Jim Thompson Guest

    What makes you think resistor ratios have a TC?

    Solid ratios is the only reason we can build analog IC's at all.

    ...Jim Thompson
     
  17. Phil Allison

    Phil Allison Guest



    ** YOU called yourself a: " novice with minor experience :) "

    - was I supposed to think otherwise ?

    Your posts show a total lack of practical electronics knowledge.

    Your alleged "engineering degree " is a worthless scrap of paper.

    I absolutely stand by my comment:

    " The size and performance criteria you have come up with make it a job for
    an
    expert. "


    You still have a lot of growing to do - pal.




    ........ Phil
     
  18. Phil Allison

    Phil Allison Guest

    "mri_bob"

    ** Jeeze - this desperate Bob wanker only ever opens his fat mouth to
    change feet.

    Must be a close relative of " Joe Blow"

    Obviously, a worn watch undergoes a much smaller range of temperature
    variation than one that it not - hence the stability of its crystal based
    time keeping is much enhanced.

    Battery operated clocks rely on the INDOOR room temp having a *long term *
    average that is not too far from 25C - their makers claim an accuracy of
    about 30 seconds a month, which is nothing wonderful.

    Bob - do you have a diploma in utter stupidity or what ?




    ....... Phil
     
  19. Hi Brendan
    Standard 74HC logic can work down to 2V, and you can get low voltage
    crystal oscillator modules. Some micros like the PIC and Atmel AVR
    series can work down to 2V too. That's enough headroom for a 2xAA
    battery supply.

    You can also make your life a bit easier if needed by using a DC-DC
    converter to give you 5V from however many batteries you have.

    Dave :)
    P.S. Ignore Phil, that's just the way he is unfortunately.
     
  20. WildIrish

    WildIrish Guest

    Thanks for your help. I can potentially bump up to 3v.
    Is there any 74HC or similar products that can perform
    divisions high enough to divide down a 10mhz oscillator in only ONE
    package?
    Someone early on suggested using a pair or 74HC's to do the job, is
    there
    any off the shelf dividers in on package capable of this assuming I
    switch
    to a 3V supply?

    What dividers are used by wristwatches? they
    must take a 32768hz oscillator and divide it WAY down until it gets one
    second
    bursts to advance the stepper motors? What dividers do they use, they
    run at 1.5v right?
    Thanks. That's unfortunate, he seems to know his stuff but exibits
    social
    issues.... i'd be afraid to work with a guy like him. Phil if you read
    this,
    don't waste your time on this thread anymore, we are all tired of you
    it appears,
    and I don't need or want your help. HOWEVER, I appreciate everyone
    else's
    time and energy in helping me to bridge gaps in my knowledge.

    ~Brendan
     
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