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Thread: Laser emergency stop over ethernet

  1. #21
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    Quote Originally Posted by mccarrot View Post
    I dont understand.
    With the RED emergency button you only turn off the lasers, but NOT the galvos, and QM's. similar like a shutter, because according some document from Bill you do not need a mechanical shutter if you can turn off the laser PSU's to kill the light.

    The key switch will turn off everything to shut down the QM in case a QM fails (yes you can have problems with qm.nets) or turn off all the equipment
    when you want to prevent people to control the laser when you are not arround.

    Next week I will make a working Prototype, My keyswitch and emergency switch just arived
    One reason for this suggestion may be that one might want to close the shutter before a show to allow the DPSS lasers to warm up some of the lasers take about an 30+ minutes to get to full power. Another reason is that an extra fail-safe is always good. But for a prototype a proof of concept is really satisfying, you can add bells and whistles after .

    Of course post lots of pictures!

    -Adam
    Last edited by sugeek; 03-12-2009 at 09:38. Reason: meh
    Support your local Janitor- not solicited .

    Laser (the acronym derived from Light Amplification by Stimulated Emissions of Radiation) is a spectacular manifestation of this process. It is a source which emits a kind of light of unrivaled purity and intensity not found in any of the previously known sources of radiation. - Lasers & Non-Linear Optics, B.B. Laud.

  2. #22
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    I have adjusted the schematic a little bit .

    I think I cannot make a Laser emmision indicator in the Safty switch box, so I made the indicator in the laser.

    I also split the 230V equipment shutoff and the switch into 2 parts, so I dont have any high current running trough my switch.

    If you are only running 1 QM.net its also possible to work without the network switch, but you will loose the option to power down the QM.

    Please tell me wat you think.
    Attached Thumbnails Attached Thumbnails dodemansknop v21.jpg  


  3. #23
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    If you plug a computer into the switch with your design, you are very likely do do damage. My suggestion would be to connect the 2 wires in each pair together.. Sure, now you can only have 1 switch, but you are a lot less likely to blow anything up.

    Is a switch to kill power to the qm.net really necessary?
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  4. #24
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    Why should I damage the PC? the pairs I'm using are the PoE pairs, and can handle upto 48V. When you connect your PC to a PoE switch with 48V on pair 3&4 nothing damages.

    When I was toghether with Hugo doing the QLIMAX show with 20 lasers/QM's in a truss due to a strange problem he lost half of the QM's and needed to power down the QM.nets to get them online again.

    Hugo is using the same method by switching off the lasers/QM.net with the keyswitch, but hugo got a QM.net in each laser head.
    Attached Thumbnails Attached Thumbnails P1280532.JPG  


  5. #25
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    Quote Originally Posted by mccarrot View Post
    Why should I damage the PC? the pairs I'm using are the PoE pairs, and can handle upto 48V. When you connect your PC to a PoE switch with 48V on pair 3&4 nothing damages.
    The 1000base-T spec requires 1500 volt isolation on every pin, so yeah, no damage.

  6. #26
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    opps, my bad
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  7. #27
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    Quote Originally Posted by heroic View Post
    The 1000base-T spec requires 1500 volt isolation on every pin, so yeah, no damage.
    I have been thinking about this. Sounds like you know a bit more than I do, so let me know your thoughts.

    My understanding, is the network pairs are transformer coupled inside a switch, NIC, etc, right?

    Surely putting a dc across the coupling transformer ( like what would potentially happen with the above diagram) is going to result in a dead transformer?

    POE uses both conductors of each pair as either positive or negative, I as assuming it was done for this reason..
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  8. #28
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    Quote Originally Posted by dave View Post
    I have been thinking about this. Sounds like you know a bit more than I do, so let me know your thoughts.

    My understanding, is the network pairs are transformer coupled inside a switch, NIC, etc, right?
    They're sometimes coupled capacitively and then inductively using pulse transformers; sometimes they're just capacitive.

    -J.

  9. #29
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    Why should I damage the PC? the pairs I'm using are the PoE pairs, and can handle upto 48V. When you connect your PC to a PoE switch with 48V on pair 3&4 nothing damages.


    Be very cautious here, true PoE is negotiated between the end device and the switch supplying the PoE. The port will not be powered until the PoE switch has determined that the device on the end is a PoE device.
    PoE can be done in two ways, either across the data pairs (for 1000base-t) or in the spare pairs (for 10/100Base-T)

    The cheap (Dlink, Netgear, etc) do a fake PoE by sending 5 or 12 volts down the spare pairs but like Dave suggested they use one pair for the positive and the other pair for the negative. However they still have a disclaimer cautioning the end user over the use of the devices and to ensure that there is one on each end.

    Another thing is that 1000Base-T can use all four pairs of the Cat5E cable unlike 100Base-T that only uses two pairs. This will be a problem if you get a gig switch as the spare pairs won’t be spare.

    The 1000base-T spec requires 1500 volt isolation on every pin, so yeah, no damage.
    Are you sure this is correct? How would you transfer data if it’s isolated on every pin?

    My understanding of how the isolation is achieved is by using a isolation transformer at the connector connected across the individual pairs, and the isolation is between the cable pairs and the electronics.

    So I don’t think it would be a good thing to accidently passing constant DC into it.
    So by all means do this but just be careful, you really don’t want to blow you NIC up in your laptop before a show
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  10. #30
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    Quote Originally Posted by loopee View Post

    Are you sure this is correct? How would you transfer data if it’s isolated on every pin?
    It's AC coupled at a rather high frequency. PoE uses both pairs because cat5 cable's not very thick and high currents tend to both heat it and induce fields which mess up the RF properties of the dielectric.

    -J.

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