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  1. #1
    polyglot's Avatar
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    Free f-stop timer?

    That's free as in libre, not gratis.

    I've just about finished building my f-stop timer. Without blowing my trumpet too hard, it has most of the features of the commercially-available units and is easier (especially for beginners) to use.

    It's based on an Arduino, which is a very accessible platform. If you can follow a schematic and solder, you could build this; if you can program in C++, you can improve on it. No programming skills are required though, that part is all complete.

    Do people have a serious interest (not just dreaming) in building this from GPL schematics and source code? Total cost for a unit would be in the ballpark of $40-60 plus a few hours of your time for assembly (basic electronics & mechanical aptitude is required). If there is sufficient interest backed with prepayment, I could have a small run of PCBs made up to simplify construction greatly and that would raise the cost by maybe $10-20/unit.

    Features are:
    - 0.01 stop resolution
    - drydown correction with 0.01 stop resolution
    - timing to approx 1ms resolution
    - max exposure 1000s, min exposure 10ms (limited by enlarger warmup)
    - direct numeric entry of EV in decimal stops with 4x4 keypad
    - can save/load 7 print-programs to/from flash
    - up to 8 exposures per program
    - each exposure has a 14-char textual description to prompt you
    - exposure footswitch and focus mode
    - menu-driven operation with text prompts
    - audible success/fail notifications
    - transfer saved programs to/from PC (future feature)
    - 16x2 red-backlit LCD with layer of rubylith to make it safe
    - adjustable LCD backlight brightness

    Major things it lacks at the moment:
    - support for more dodges than the base exposure (e.g. three separate 1-stop dodges), i.e. concurrent dodges / operator-is-an-octopus mode
    - closed-loop mode and enlarger warmup correction
    - split-grade automation (input a contrast change, have it calculate new times)

    They're not things I need at the moment, so are lower priority.

    I'm online for only another week and then off for five weeks so I'll post photos etc of the timer after I get back in October. Let me know your thoughts.
    Last edited by polyglot; 08-19-2011 at 11:06 AM. Click to view previous post history.

  2. #2

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    Very interesting project. Gets me thinking, so I have a question or two along these lines.

    Would enlarger warmup correction be implemented by some sort of calibration that the user would have to obtain and apply? Or would it make sense to put a photocell in the enlarger housing so that it would integrate the warmup photon rate? I could imagine that a hot bulb would warm up faster than a cold one. A sensor in the lamp housing would seem to be a very desirable way to go.

    As to interest in building the unit, I haven't given it much thought as I've got a very nice basic timer (00.0 to 99.9 s). Drydown correction would be good to gain. I wouldn't spend on a fancy factory made unit, but I'd enjoy the handiwork of building a unit and could probably talk myself into a $50 to $80 unit. Without seeing and pricing out costs locally here, I'd guess that it would be at the high end, just on the idea that stuff always seems to be more expensive in the end.

    Does yours have battery backup or some power feature, perhaps with line voltage passthrough output socket so that it can keep a program or menu choices or parameters such as the drydown percentage?

    There is something to be said for putting lots of rotary knobs on a unit so you can dial in the time since that changes the most frequently. Punch up/down buttons for time work reasonably well. Is the main time controlled by menu only?

    I have yet to try split-grade printing but it sounds exciting, and smooth automation for that sounds inviting.

    Personally I'm intrigued and want to encourage you but can't commit to anything right at this instant. Thanks for your work and sharing and good luck with the project.

  3. #3
    yeknom02's Avatar
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    I am a big fan of electronics projects, so if no interaction with a computer is required, I'm definitely interested. I have recently thought about the Darkroom Automation timer, which looks great but simply unaffordable at the moment. I have been wanting to try split-grade printing, though, so that feature would be very welcome in my book.

    One thing I am interested in is the power setup. The Paterson Digital timer I have now just has one outlet for the enlarger, but I wonder if it's possible to have another constantly powered outlet for, say, my safelight.
    "When the going gets weird, the weird turn pro." - HST
    My Flickr Gallery

  4. #4
    billdlv's Avatar
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    If the cost to build was around 50-60 us $ I would be interested. I have an existing timer already but I have wanted a f-stop timer for a while. I too have looked at the darkroom automation units and they look quite nice, but too expensive for me as well at the moment.

  5. #5
    Barry S's Avatar
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    I'm definitely interested as I'd love an f-stop timer and don't mind a bit of soldering. Put me down for a PCB.

  6. #6
    Dave Swinnard's Avatar
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    I too would be interested, especially if I didn't have to make my own PCB.

  7. #7
    samcomet's Avatar
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    Definite interest from me too! congrats and cheers for now, sam

  8. #8
    ghostcount's Avatar
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    +1 LMK when.
    “I drank what?” - Socrates

  9. #9
    hoffy's Avatar
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    Add me to the list

  10. #10

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    Quote Originally Posted by polyglot View Post
    That's free as in libre, not gratis.

    Total cost for a unit would be in the ballpark of $40-60 plus a few hours of your time for assembly (basic electronics & mechanical aptitude is required). If there is sufficient interest backed with prepayment, I could have a small run of PCBs made up to simplify construction greatly and that would raise the cost by maybe $10-20/unit.

    .
    That isn't free! Must be new math or did I miss something here?

    Do you also give free HD for life for only $100/month?

    .
    Anyone can make a Digital print, but only a photographer can make a photograph.

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