About EEVblog

Check Also

EEVblog #1035 – Flaming DIY Power Supply

Smoke in the EEVblog Lab! What component failed and caught alight in the RD Tech ...

  • Nice Video, thank you very much.

    But you have a little mistake in the beginning:
    An omnidirectional laser scanner is still NOT a 2D-Scanner. It scans 1D Barcodes in any orientation, but no 2D-Codes like QR-Codes or such.

    (You just mentioned it once as a side note)

  • Hi Dave

    This video says it is private!!! I hope it’s not just me.

    Cannot view it.

    Regards
    Jerson

  • “This video is private”

  • For me it also showing “Private Video!”
    Nothing to watch…

  • aaaa asfasdf

    same here. maybe he is editing the video to reflect the mistaken identity of xcanner.

  • Drone

    02 July 2014 11:15AM UTC, “This video is private. If the owner of this video has granted you access, please log in.”

  • Chris

    I wake up this morning all excited to see a new teardown video to watch with my breakfast! 🙂
    Then it tells me it’s private. Now I’m bummed. 🙁

  • Paul

    It’s a private video what the

  • Ronald

    The m4v file is also going really slow.

  • Now working. Thanks Dave.

  • Adrian
  • Fred

    Thanks Adrian for the link mine showed removed by user

  • Drone

    02 July 2014 1530 UTC, Adrian’s link to the video is working. Video in Dave’s post now showing “Removed by User”. Thanks Adrian. Likely Dave has turned in for the night as of my post time I’m sure he’ll sort it out later.

    Regards, David in Jakarta

  • Great video Dave. Just one thing to note, these units use an RJ50 (10 pins) not RJ45 (8 pins)

    Cheers
    Dan

  • Richard

    Of course it wont work if you block the laser…

    The laser dot passes along the barcode (at some point in its complex path) and the *single pixel* photosensor sees the reflected light as a time series of light(er)/ dim(er) pulses.

    You could illuminate the barcode with a separate single light of the laser diode frequency and … nothing would happen.

    You could illuminate the barcode with a laser pointer (of the correct ‘colour’ ) flicked along the code once and…it should work.

    The processor is ‘simply’ constantly monitoring the photodiode sensor for time series bit patterns that decode as valid after checksums etc.

    Even the speed of scan is probably highly variable – so long as it is reasonably constant within the barcode so constant bit timing can be established.

    • Johm

      Even on 1D scanners, the sweeping speed has to be sinusoidal due to the nature of the motor that swings the mirror. I bet there’s serious processing to get the bit rate right…

      • Richard

        The mirror and the motor on Dave’s teardown rund continuously at constant speed. The result is a constant speed of dot movement, not sinusoidal.

        THink of the motor as having a constant angular speed – each unit of time it moves through the same angle. The mirror flat surface thus also moves the same…even if it is offset. The laser is fixed and the reflection is twice the angle of incidence, so twice the angular speed = constant.

        The slight trig variations come in as the laser reaches the barcode – whchis mostly flat, not arranged in a nice cuve at constant radius from the laser, but it is in the small part of the ‘opposite’ leg of the triangle with a long ‘Adjacent’ and ‘hypotenuse’, so Sin errors are tiny.

        There may be some units out there that have an oscillating mirror, and sine is the most mechanically sympathetc way of doing that, but there would still be vibration.

  • Richard

    (Still saying ‘removed by the user’ but I found it on your channel…wrong link here?

  • Echo

    I agree with Richard, I think you overestimate a little bit the level of processing required on board. When the LASER is doing its job scanning the barcode, the photosensor just has to read the time patern of the light it receives without actually caring where it read it. I’m guessing it would look like that:
    Bandpass filter > Protocol decoder(s) > Interface to computer.
    Add to that a control loop on the motor speed and you have it. I really don’t expect it to do “much” more than a decent infrared type decoder that would do different protocols, since the scanning motor makes it all come back to the time domain. (minus the IR modulations maybe)
    But the tricky business must come when the scanned barcode is flexed because that has the apparent scanning speed of the scan vary during the read. That is what must actually require some processing power to filter…

    I hope I’m making sense…

  • Chris

    That was really interesting. Would it be possible to probe the photodiode with the oscilloscope to see what the output looks like? I’ve always been curious to know what the scanner sees. Thanks.

    • Johm

      Thumbs up on a followup video hooking up the oscilloscope to see which protocol is being used. A bit like the IR Remote Hack Video.

  • The part at 20:27 looks a lot like a reflective interrupter eg OSRAM, SFH 9202.

    Probably to detect the motor speed via the reflective sheet covering a quarter on main motor (22:25)

    At least that is what I did with it back in the days. I think that was also the first SMD component I ever soldered.

    Thanks Dave for the EEV Blog!

The EEVblog Store generally ships twice a week, on Tuesdays & Fridays, Sydney time. Dismiss