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Thread: Open Source Scanfail Unit (phase 1)

  1. #91
    Join Date
    May 2007
    Location
    Sydney, Australia
    Posts
    81

    Default Two chip challenge

    Ok, Here's my take on a very simple scan fail detector
    I've tried to keep it down to just two chips - the Bill Benner " two chip challenge"

    1 x LM423 quad opamp and 1 x LM339 quad comparator

    It seems to work in simulation, at least with the waveforms I've tried feeding into it.

    By placing this circuit on the forum I'm making no comment about it's suitability for any purpose at all.
    So- !!AT YOUR OWN RISK !!

    I imagine that it's similar to what Dave's working on, except his actually works with real signals.

    Some notes:
    1/ If you're going to try making this circuit, be carefull as all the component values are guessed.
    'Cos it works in simulation means that it may be super unstable in real life.

    2/ It would be bad if any signal were to be fed back into the feedback output of the scanner.
    Better choice of R11,C4 ,R15, C5 would help , or another opamp as a voltage follower
    would stop that, but would add another chip.

    3/ The negative supply rail for the opamp reads "+V-15". Don't ask. It's a Circuitmaker2000 thing.

    4/The summing amplifier is a bit stodgy, but it seems to work

    5/ The three 5.1v zeners D1,D2,D3 on the output stop badness from getting to the mod. inputs of the lasers.

    Waveforms:
    1/ Position detector inputs.
    Green is point A on the schematic (X axis) - a flat sheet that periodically collapses
    Yellow is point B (Y axis) - a few random jumps at varying speeds



    2/After differentiation.
    Green is point C - super clipped
    Yellow is point D - small signals.



    3/ After Rectification -
    Green is point E
    Yellow is point F



    4/ Output stuff
    Green is point G - the output of the summing
    Yellow is point H - the threshold voltage
    Cyan is point J - the "shutter" output, floats high through the LED, pulls low during fault.


    The first collapse of the X axis is deemed safe , as the Y axis is moving fast, whereas the 2nd,3rd,4th and 5th collapse
    are deemed unsafe because the velocity of the Y axis is too slow.
    The ringing on the cyan output trace is some sort of interaction between the comparator and the LED to the +15v supply. The modulation outputs shouldn't be effected like this. But if they are the 5.1v zeners are there...

    Sometime over the next week I'll try to make a proto of this circuit, but if anyone feels adventurous.....
    Cheers,
    BF
    ( first post with images - sorry if I've blown the page width out. I'll learn for next time)

  2. #92
    Join Date
    Nov 2005
    Location
    Melbourne, Australia
    Posts
    3,702

    Default

    Well, I have a very close to working prototype I think.. A major source of annoyance over the last couple of times I have done anything, has turned out to be noise from a shitty Chinese Switch mode supply. I tested the circuit I have with a set of widemoves tonight, and the noise I was seeing has disappeared

    Ill get a bit further over the weekend
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  3. #93
    Join Date
    Dec 2007
    Location
    Stockholm, Sweden
    Posts
    551

    Default

    Did anyone get some good results from the experiments in this thread?

  4. #94
    Join Date
    Nov 2005
    Location
    Melbourne, Australia
    Posts
    3,702

    Default

    I have pretty much a working prototype.


    I want to make up a few, and get a couple of people to put them thru their paces Hopefully in the next few weeks if I can find some time
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  5. #95
    Join Date
    Oct 2006
    Location
    Cleveland, Ohio
    Posts
    2,342

    Default

    great, keep me in the loop

  6. #96
    Join Date
    Dec 2007
    Location
    Stockholm, Sweden
    Posts
    551

    Default

    ...the feedback loop?

  7. #97
    Join Date
    Nov 2005
    Location
    Melbourne, Australia
    Posts
    3,702

    Default

    Quote Originally Posted by drlava View Post
    great, keep me in the loop
    No worries. If you want, when I'm done with a board, ill shoot you one as well?
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  8. #98
    Join Date
    Apr 2008
    Location
    Amsterdam, NL
    Posts
    2,098

    Default

    Hi dave, any updates about this project?

  9. #99
    Join Date
    Nov 2005
    Location
    Melbourne, Australia
    Posts
    3,702

    Default

    Not yet - gotta get a few things finished, then back on to this
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