11 comments on “Variable Contrast LED Head for Durst 138S

  1. Pingback: » Variable Contrast LED Head for Durst 138S – Condensers Tripping Through The Dark

  2. Great work sir! I have a couple questions…

    – after some time now, which method works best.. the converted condensors, the point source, or the leds with the opal/milk glass in the heat glass slot. I am considering following in your tracks and would appreciate your recommendation here. Also, would you happen to have a bill of materials detailing which specific parts you used?


    • I use the diffusion (converted condensers) source the most. I can’t say why that is, but laziness is probably a big part of it since I switch back and forth a lot between film formats. With the condensers there’s a bit more setup time to pick the right pair of condensers for the format.

      I don’t have a detailed bill of materials yet. A recent thread on the Large Format Forum (http://www.largeformatphotography.info/forum/showthread.php?119413-Building-a-Variable-Contrast-LED-head-for-a-Durst-138) has got me looking into refining the build process. As part of that I will be putting together a bill of materials. I also hope to test a few varieties of blue LEDs and a new LED driver, and a more standard power supply. Finally I hope to get a printed circuit board designed so others can have an easier starting point for the build.

      However the main components I used are:
      1x Arduino Mega
      4x http://www.ledsupply.com/led-drivers/buckblock-1000ma-constant-current-led-driver-with-dimming
      4x 2N3904 transistor (or equivalent)
      4x 10K resistor
      12x CREE XT-E Royal Blue LEDs
      12x CREE XP-E Green LEDs
      30V Meanwell power supply
      1x 4×4 Alphanumeric Keypad
      1x 4×20 LCD display blue (with rubylith over it)
      1x SD card reader
      1x power reducer circuit to power the arduino from the 30V power supply.

      There were also two cases, some homemade cables (DIN 8 conductor ends), the Durst Condenser frames, CAT45 patch cable and connectors, various pin headers, and other miscellaneous electronic components.

  3. Thanks for the details Larry! I am very much interested in your work… Here’s where I’m at:

    – I recently picked up a 138S with all the condensers and ordered a few different bulbs and some diffusion glass to mess around with that side of things.

    – A few months back I was in touch Brodie Tyrell, bought his circuit board, and just about all the components for his f stop timer, but in the mean time came across good deal on an RH Designs model, which put that project on hold. I must say, that I don’t have an engineering background.. I’m more of a paint by numbers guy, so I’d be looking for the semi baked version of the code when and if that comes along… Bottom line, I’ve got the project box, arduino board, and all the components for the f stop timer which I may or may not build depending on how you proceed with your project.

    – Today I picked up a a couple scratched Latico condensers, so I’m set there..

    Basically, I’d like to follow in your footsteps, so I hope you continue this project… In the meantime I’m going to pick up the led’s and related hardware.. In the meantime, since some time has passed.. Are the 4 Buckblock controllers the final solution or did you run across anything else since then that my allow the use of a single controller for each bank? How are these controlled in the mean time before going the arduino route? Via potentiometers of some sort?

    Thanks for your feedback!

  4. John, There’s now a thread on the Large Format Forum on this: http://www.largeformatphotography.info/forum/showthread.php?119413-Building-a-Variable-Contrast-LED-head-for-a-Durst-138

    In the thread I mentioned that I want to look at the new FlexBlock drivers (http://www.ledsupply.com/led-drivers/flexblock-700ma-constant-current-led-driver-with-dimming). These should drive 12 LEDs each, and may also allow the use of a 12V power supply (PC or otherwise). If so that would simplify the design a bit.

    I’m also hoping to design a printed circuit board like Brodie Tyrell did. That should significantly simplify the build.

    You could use a potentiometer to dim them as well. Ideally you could find a double stacked potentiometer that would dim one while the other gets brighter. Then each grade could just be a single marked position, and the speed might be somewhat matched. You wouldn’t need an Arduino, however you would need a timer.

    I haven’t tested how fast the drivers turn on from a cold start, so controlling them with a timer may not work well. Note that the timer would also be turning on the DC power supply, which also likely has a noticeable startup lag. The Meanwell 30V one I used also has a shutdown lag where it provides DC power for a second or so after the AC is turned off. That would not work controlled by an external timer that switches AC.

  5. Great.. I’ll pick up the thread…

    In re the timer, I thought you were using a relay to control the lights at the 12 volt stage (after the xformer) which was instant?? So in terms of using pots, couldn’t I power up the whole thing, assuming I’m using a relay to turn the lights on and off via an f stop timer, put the timer into focus mode (or similar).. turn it on an off a few times to make sure it working, and then proceed to print…? Switching the pots (grade) in between prints? Am I on the right track?

  6. Actually I have a relay on my setup, but it’s only to turn the safelights on and off. The LEDs are turned on, off and dimmed by PWM (setting a pseudo output voltage) on 4 separate pins on the Arduino. The driver is always energized, but only lights when the Arduino signals it to. The relay for the safelights is also triggered at the same time.

    But if you use the pots for dimming instead of PWM you’d need to find an alternate way of switching them on and off once the pots are set. Relays could work, but most timers won’t directly control an external relay.

  7. I don’t intend to spam/pollute the comments on this post, but just saw a Durst Laborator 138S for sale on Craigslist near DC and found your blog (and the enlarger manual pdf – thank you!) on your website while trying to do some research. I know it’s a bit late in the game to shop around for enlargers and parts, I’m looking at going with a Beseler 23C – though this 5×7 would let me enlarge my 6×17 negatives!!! Tempting… just wanted to share in case any of your audience may be interested:


  8. Hey Larry,

    Any updates on this project? I built an adapter plate out of aluminum to mount a Super Chromega D II to the 138S and it’s been okay, but it can barely do 4×5 due to the 5/8″ or so gap between the adapter plate (3/8″) and the nega138 carrier.. the Chromega D appears to have been designed to have the neg carrier flat up against the bottom of the head… Long story short, I keep coming back to your project as possible path moving forward…. Any news on a BOM? Any updates on the code on github? Would appreciate any feedback you can provide..



    • John,

      Unfortunately I’ve gotten very busy with work and it has sidelined this project. I haven’t even made it into the darkroom for simple printing in 3 months or more. I do still plan on reworking the head and producing a BOM, printed circuit board and some updated code.


      • Thanks for the update Larry. Sorry to hear about the project being sidelined. I can definitely understand getting tied up in work though. I’ll stay tuned…

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