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A little success

Discussion in 'Electronic Design' started by Ignoramus27362, Oct 23, 2005.

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  1. I bought 10 555 timers to play with, to learn a little bit how to put
    real circuits together. At $.25 each, they are cheaper to ruin that
    XR2206, at $3.69 each. I finally was able to put an astable oscillator
    oscillating at about 200 Hz.

    i
     
  2. Robert Baer

    Robert Baer Guest

    ....and, in the process, you learned a few things electronic.
     
  3. Rich Webb

    Rich Webb Guest

    Which is A Good Thing. Nobody is born knowing about this stuff and
    pretty much everybody has let the Magic Smoke out of a few things along
    the way. Hang in there, Ignoramus27362!
     
  4. Terry Given

    Terry Given Guest

    but be *VERY* careful when messing with the big stuff - its the
    difference between "oops, there goes a 555" and "Oh ****, where are my
    fingers"

    Cheers
    Terry
     
  5. John Fields

    John Fields Guest

     
  6. yep... very many things...

    i
    --
     
  7. Yep... It is somewhat like computer programming, using logic to debug
    things and verify assumptions etc.

    i
    --
     
  8. Boris Mohar

    Boris Mohar Guest

    Here is something to implement at the later date in your project. My Lincoln
    175 which I use primarily for tig welding has a fixed time for Argon post
    weld flow. This can waste a lot of gas if you are stitching and touching up
    the welds the do not stay very hot for long time after the arc has
    extinguished. The post flow time should be based on the duration and current
    used at the time of the last weld. This is a job for a micro but it could be
    done with discrete circuitry. Since I still feel very much like a newb at
    this, I'd appreciate any comments.


    Regards,

    Boris Mohar

    Got Knock? - see:
    Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca

    void _-void-_ in the obvious place
     
  9. I think that what you say makes sense. I would say, go for it, but
    have a lower minimum on postflow time to avoid programming bugs
    ruining your tungstens.

    On my welder, postflow time is settable. I can say that, for example,
    postflow should be 8.4 seconds and preflow should be 5.3 seconds and
    starting current would be 44.8 amps and the welding current would be
    78 amps and the time to reach welding current should be 3.2 seconds
    and s0o on and so forth. It is a programmable welding machine, which
    is kind of nice.

    Later on, when I am done with my current inverter project (whether I
    succeed or blow up the IGBTs), I may try to do an automatic welding
    setup where the tig torch is moved along a straight line at a
    predetermined speed and the welder is controlled from a linux laptop,
    let's say. But I should not scatter myself too much, right now I am
    focused on the inverter.

    i
     
  10. You want a circuit that models the temperature rise of the tip and
    also the cooling time for that temperature rise. An RC time constant
    is probably a model that is good enough. Charge a capacitor through a
    resistor with a fixed voltage that represents the steady state tip
    temperature (this should be higher when the current is higher). When
    the current goes to zero, this voltage will also be zxero, and will
    discharge he capacitor through the same resistor. When the cap
    voltage falles below some fixed threshold, representing the safe tip
    temperature without gas, switch the gas off.

    In parallel, I would have a single shot that switches the gas on
    immediately when current starts (unless you can figure out how to have
    it anticipate the current) and holds it on for a minimum time,
    regardless of what the cap is doing.
     
  11. But there's a significant difference - if you crash a program, it
    doesn't usually let the smoke out - you just edit it and run another
    edit/compile/run/debug cycle.

    With real parts, when you let the smoke out, you actually _learn_
    stuff. :)

    Good Luck!
    Rich
     
  12. Well, obviously, the place to start looking is at the current post flow
    timer/regulator. It might even have an adjustment already. But if not,
    then find out just exactly what the mechanism does, to figure out what
    you need to do to control it. (timer relay? dashpot?)

    Please report back here with the results of your investigations. :)

    Good Luck!
    Rich
     
  13. It depends on what kind of software you are talking about.
    Seriously. Around where I work, software bugs == lost money.

    You do have a point though, but these chips are not terribly
    expensive. I ruined a $0.29 555 timer, and a $3.59 XR2206, so far, no
    big deal.

    The amount of time that I spent on this project, already, is enormous
    and dwarfs the cost of chips by at least 2 orders of magnitude.

    I have piles of used 1960's circuit boards with plenty of free
    components too.

    i
     
  14. By the way, Rich, do you have any thoughts regarding my XR2206 issues
    (see my separate thread on that). The square wave output works, but
    has too low voltage.

    i
    --
     
  15. Rich Grise

    Rich Grise Guest

    Well, I've already posted my thoughts, which are, in a nutshell, the
    polite way, start small. Get an XR2206 working on a breadboard reliably,
    and _then_ start playing with jacking up the output voltage and stuff.

    And read.

    Good Luck!
     

  16. Getting an XR2206 working on a breadboard reliably is exactly what I
    am working on.

    It kind of half works.

    It produces pulses. I can see them on my scope.

    The trouble is that the pulse amplitude is too small. The variable
    duty cycle application that makes the chip change the timing resistor
    for top vs. bottom of the cycle (which changes their relative
    duration), involves sending over 2V to pin 9, from the output on pin
    11. My output is about 0.67 volts in amplitude. That's my current
    issue.

    i

    --
     
  17. May I suggest an experiment? Remove the pull up resistor from the
    output and see what the output does. Also, measure the pull up
    resistor with an ohm meter (while it is out of the circuit).
     
  18. I will try that. I have a vague feeling that I already tried, but I am
    not sure.

    I am considering that sticking a comparator chip between 9 and 11, if
    all else fails. But I would rather understand what is wrong, rather
    than pile up mistakes.
    Sadly, I definitely did that. It checks out at 5.01 kOhm with my
    multimeter. It is a takeout from a '1969 circuit board.

    i
     
  19. 1 down, unknown to go.
     
  20. Tim Williams

    Tim Williams Guest

    Hey Iggy, if you want PWM, just grab a UC3842 from a dead monitor board, or
    at worst, send a buck to a mail order catalog. If you're headed for a half
    or full bridge circuit you'll want dead time too, in which case a TL494
    might be better. (3524 / TL494 / KA7500 type chips are push pull output,
    not overall variable duty cycle, so I don't really know what you could get
    that's a cross between them..)

    Tim
     
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