Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,593   Posts: 1,546,100   Online: 906
      
Page 3 of 4 FirstFirst 1234 LastLast
Results 21 to 30 of 31
  1. #21
    Worker 11811's Avatar
    Join Date
    Jan 2010
    Location
    Pennsylvania, USA
    Shooter
    Multi Format
    Posts
    1,620
    Quote Originally Posted by Curt View Post
    It that a 74AC14 Hex Schmitt-Trigger Inverter?
    Curt;

    Yes, it is an inverter. I did Google this page but that's why I picked it... because it was what I remembered using in Vo-Tech classes all those years ago. I did not specifically remember the Schmitt trigger inverter but I did remember that there was an RC circuit that you could use to make PWM that used a certain inverter chip. It was only partly from memory but mostly from looking it up.

    Quote Originally Posted by BetterSense View Post
    Making your own PWM circuit is a valid exercise, but LED drivers are pretty cheap and available. I bought a digitally regulated, multi-mode driver board for a homemade flashlight on Dealextreme.com for $1.63 with free shipping. So there are probably ready-to-go PWM led drivers available, especially with LED becoming more popular for household lighting.
    Better Sense;

    You're right. There probably is an IC that does it all for you but this is the way I think. If you can find such an animal there's no reason not to use it.

    You're talking to the guy who spent the better part of a weekend aligning his enlarger to within 140 microns. How else do you think I'd go about it?

    Randy S.

    In girum imus nocte et consumimur igni.

    -----

    http://www.flickr.com/photos/randystankey/

  2. #22
    Curt's Avatar
    Join Date
    Sep 2005
    Location
    Pacific Northwest
    Shooter
    Multi Format
    Posts
    4,553
    Images
    15
    Thanks, how do you align the enlarger to the precision of 140 microns? If I can find a better way I won't go wandering at night and be consumed by fire.
    Everytime I find a film or paper that I like, they discontinue it. - Paul Strand - Aperture monograph on Strand

  3. #23
    Worker 11811's Avatar
    Join Date
    Jan 2010
    Location
    Pennsylvania, USA
    Shooter
    Multi Format
    Posts
    1,620
    It was a joke. It was in another message thread where I was talking about the amount of leeway one has when focusing. It was all theoretical, really, but Better Sense said that I have better things to do than count the number of microns within which I can focus my enlarger. It was all good natured banter, actually, even though he was right. (And, I did just go make some prints. )

    So, the point was that he caught me, once again, behaving somewhere in the territory between "anal retentive" and "O.C.D."

    The bottom line is that I built my electronic circuit out of an IC and several discrete components where Better Sense advises that there might be a monolithic solution to the problem. He's probably right and I agree it would be a better solution if it were not my tenancy to do everything the hard way.

    BTW: In over four years of using that conundrum in my signature line you are one of only two people have said that they understand it. (Or, at least, people who have admitted to understanding it. )
    Randy S.

    In girum imus nocte et consumimur igni.

    -----

    http://www.flickr.com/photos/randystankey/

  4. #24

    Join Date
    Jan 2007
    Location
    Sydney, Australia
    Shooter
    Multi Format
    Posts
    303
    Images
    1
    Quote Originally Posted by srs5694 View Post
    (re: red LEDs)
    I'm not the one who designed and built it, but if they're the right color (and if the blue and green LEDs are the right color), the whole setup could be used for color printing, too. This would be conceptually very similar to a Philips Tri-One enlarger, which uses halogen bulbs behind red, green, and blue filters to provide light for VC B&W and color printing. I've got one of the Philips machines and it works quite well.
    Of course it could I plan to make a 'graflarger style' back with LEDs for just this purpose.

  5. #25
    Steve Smith's Avatar
    Join Date
    May 2006
    Location
    Ryde, Isle of Wight
    Shooter
    Medium Format
    Posts
    8,600
    Images
    122
    Quote Originally Posted by Thomas Bertilsson View Post
    So you balance contrast by altering how many green and how many blue diodes are illuminated?

    It's great to be able to focus with green light also, because that's the color our eyes are the most sensitive to.

    Forgive my ignorance, but what are the red LEDs for?
    The contrast is balanced by the relative times the blue and green LEDs are on. It has red LEDs because it uses the PCB from an LED stage light. The red is useful for checking the easel alignment or for working out where to dodge or burn a bit like the red filter on some standard enlargers.


    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  6. #26
    Steve Smith's Avatar
    Join Date
    May 2006
    Location
    Ryde, Isle of Wight
    Shooter
    Medium Format
    Posts
    8,600
    Images
    122
    Quote Originally Posted by Worker 11811 View Post
    How handy are you with electronic circuit building?
    Can you make a pulse width modulation circuit to control the brightness of the LEDs?
    I can indeed and suggested this yesterday:

    Quote Originally Posted by Steve Smith View Post
    I am then going to work on a switch mode controller with a single control so that fully anti-clockwise the duty cycle is 100% green and 0% blue. Turning the control clockwise will increase the duty cycle of the blue and reduce that of the green so at the mid point they both receive 50% and fully clockwise it is 0% green and 100% blue. This will give me a single Contrast control.
    The circuit I will use is one I have used before. It is almost a standard astable multivibrator but the base resistors to the two transistors are connected via a two diode and potentiometer circuit similar to the one in your link. There will then be a suitably large darlington transistor connected to either side to drive the green and blue channels.


    Steve.
    Last edited by Steve Smith; 07-17-2010 at 03:29 AM. Click to view previous post history.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  7. #27
    BetterSense's Avatar
    Join Date
    Aug 2008
    Location
    North Carolina
    Shooter
    35mm
    Posts
    2,867
    If I built an LED enlarger, I would probably use a darlington transistor hooked up to the PWM outputs of a microcontroller, since I have microcontroller infrastructure already. Then you could control the R, G, B lights digitally as well as create automated recipes, or have feedback from a photosensor, creating a closed-loop exposure system.
    f/22 and be there.

  8. #28
    Steve Smith's Avatar
    Join Date
    May 2006
    Location
    Ryde, Isle of Wight
    Shooter
    Medium Format
    Posts
    8,600
    Images
    122
    Quote Originally Posted by BetterSense View Post
    I would probably use a darlington transistor hooked up to the PWM outputs of a microcontroller, since I have microcontroller infrastructure already.
    That's quite a logical and sensible way of doing things as you can fine tune it to be whatever you want it to be and have settings to match proper grades etc.

    However, I like to keep things simple myself so I'm going to go for my single contrast control!


    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  9. #29
    Worker 11811's Avatar
    Join Date
    Jan 2010
    Location
    Pennsylvania, USA
    Shooter
    Multi Format
    Posts
    1,620
    So you're using the Darlington transistor so you can get more current out of the system to drive all those LEDs.
    Whereas, my idea would be suitable for a couple-few LEDs at most and would peter out if I tried to drive a dozen or more of them, such as you plan to do. Right?

    (P.S. - I read you were going to make a "controller" but I skimmed over the words "switch mode".)
    Randy S.

    In girum imus nocte et consumimur igni.

    -----

    http://www.flickr.com/photos/randystankey/

  10. #30
    jeroldharter's Avatar
    Join Date
    Nov 2005
    Location
    Wisconsin
    Shooter
    4x5 Format
    Posts
    1,958
    Images
    1
    Good stuff.

    Easy for me to say given that I know nothing about electronicsf, but I wish that an entrepreneurial sort here would devise 2 items:

    • A simple, adaptable LED variable contrast light source for 4x5 and 8x10
    • A simple Jobo alternative, something like an electric screwdriver turning a drum in a water bath.


    Now that Aristo is moribund and the bulbs are currently out of production there could be a market for the light sources. Likewise with Jobo and everyone paying $500 for drums.
    Jerold Harter MD

Page 3 of 4 FirstFirst 1234 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin