Unknown Schematic Symbol

Discussion in 'Homework Help' started by shredability, Aug 2, 2012.

  1. shredability

    Thread Starter Member

    Apr 1, 2012
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    [​IMG]

    "
    IL1
    NE2X
    Ready
    "

    What is that? what does it do? is it necessary?

    What should the power rating of these resistors typically be? I have 1/8w, I'm guessing that wont cut the mustard.

    And while i'm here I know that a transformer will not work on DC obviously b/c there is no change in magnetic field. But will it work on a square wave fluxuating from 0-5v w/ output from a 555, schmitt trigger or transistor?
     
  2. WBahn

    Moderator

    Mar 31, 2012
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    My guess (and it's not much more than that) is that it is a neon bulb with a radioactive source in it. If I'm right, the idea is that it will fire and turn on when the voltage from the inverter reaches a high enough voltage such that the flash could be fired.

    Without walking through the entire circuit operation and looking at each resistor individually, I can't tell. But this is a low duty cycle circuit so most of the resistors are not going to need to be too hefty. The power rating applies to the average power over a reasonable time interval (typically on the order of a second) since the issue is heat buildup. At some point, more so with the active components, the issue is breakdown voltage.

    Yes, you can send a square wave into a transformer and get something resembling a square wave out of it. The transformer will respond to each of the harmonics that make up the signal according to its frequency response, so there may be a lot of distortion or only a little.

    You will want to be sure to provide anti-kickback protection for any outputs exposed to the coil inductance.
     
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  3. wmodavis

    Well-Known Member

    Oct 23, 2010
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    It IS a neon bulb. Right on WBahn.
     
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  4. #12

    Expert

    Nov 30, 2010
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    But it's not radioactive. The dot just means, "gas filled".
     
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  5. MrCarlos

    Active Member

    Jan 2, 2010
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  6. WBahn

    Moderator

    Mar 31, 2012
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    #12 likes this.
  7. shredability

    Thread Starter Member

    Apr 1, 2012
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    Thanks for all your responses :)

    So in this schematic both electrodes are wired up but not the trigger? So essentially once the cap reaches a high enough voltage it will discharge through the light, why would this be wanted? If this is a camera flash unit, why are there two gas filled flashlamps?
     
  8. t06afre

    AAC Fanatic!

    May 11, 2009
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  9. Wendy

    Moderator

    Mar 24, 2008
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    Neon lamps fire around 90V, and will hold at 60V. A radioactive source in the gas will drop these voltages. As has been said, it is probably not a radioactive varient though.
     
  10. t06afre

    AAC Fanatic!

    May 11, 2009
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    It is common to rate neon lamps with RMS AC voltage. 65 volt AC RMS will have a peak voltage equal to about 90 volt. To the OP one thing you should know about neon bulbs. Then using a DC source. Only the negatively charged electrode will glow;)
     
  11. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The IL1 is a neon tube.
    It is used as an indicator that the flash capacitor has been charged.
    It also stops the inverter from charging the flash capacitor.

    Bertus
     
  12. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    The second one is a "xenon flash tube" it needs an outside high voltage trigger to flash/light the gas inside the tube. See this link for more detail of operation - http://en.wikipedia.org/wiki/Flashtube
     
  13. mlog

    Member

    Feb 11, 2012
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    The neon lamp is an indicator that tells the user there is sufficient charge stored in capacitor C2 to drive the flashlamp if desired. It's nothing more than a "ready" indicator. In other words, it says it is ready for you to take a flash picture.

    Back in the good old days before LEDs were cheap and plentiful, neon lamps were used as indicators. They didn't require much power and weren't that expensive.
     
  14. #12

    Expert

    Nov 30, 2010
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    Neons are still good indicators for high voltage, low current needs. This flash circuit would struggle to keep up if you tried to use a 10-20 ma LED for an indicator. Neon lamps can give a good-enough indication in the 100 microamp range.
     
  15. recklessrog

    Member

    May 23, 2013
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    Looking at the circuit it appears that the neon does two jobs, once there is sufficient charge for it to strike and glow, it indicates a "ready to use the flash" state, it also turns Q3 on via the zener diode stopping the oscillator from further charging to save the battery. As the neon probably strikes at 70-90 volts, the zener, allows some further charging until the zener conducts at 110 volts,


    Oh just noticed how old this thread is, never mind eh!
     
    Last edited: Sep 16, 2015
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