# Open source f/stop enlarger timer released

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• 08-23-2011, 09:25 AM
polyglot
Open source f/stop enlarger timer released
For those of you not looking in the other thread, I've released the source for my f/stop timer under the GNU General Public License. There's a video showing the user interface too.
• 08-24-2011, 09:34 AM
paul ron
Another video of the controller board in use... any one can do it...

http://www.youtube.com/watch?v=3xCY2K9kQz4

I found a source for populated proto boards at Mouser...

http://www.mouser.com/arduino/?gclid...FQfd4AoduAzf6A

If you google adriuno you get all sort of project ideas n free software

Very cool n versitile A/D IO board.

:D
• 08-25-2011, 03:49 AM
SMBooth
The thing I would like explained is the base exposure, in the video it set as stop (3.5 stops) I though it would be seconds then the rest is in stops calculate from that base time.
• 08-25-2011, 10:09 AM
polyglot
Quote:

Originally Posted by SMBooth
The thing I would like explained is the base exposure, in the video it set as stop (3.5 stops) I though it would be seconds then the rest is in stops calculate from that base time.

Time = 2^stops. So 0 stops is 1s, 2 stops is 4s, 3.5 stops is 2^3.5 = 11.314s.

To make a more complicated example, and illustrate how dodges are computed, consider:
base = 3.5 stops = 11.314s
dodge 1 = 0.5 stop = 2^(3.5-0.5) = 8s (i.e. dodge for 3.314)
dodge 2 = 0.25 stop = 2^(3.5-0.25) = 9.514s (i.e. dodge for 1.8s)

Therefore, the base exposure once dodges are subtracted is 11.314-3.314-1.8=6.2s. When you perform the dodges, the non-dodged areas will get the originally intended base exposure of 11.314s.

The reason the base exposure is expressed in stops is it makes it easier to scale your paper size, or to shift the whole exposure darker/lighter by a certain tone. Say you figure out a good print at 8x10 and want to print 16x20, you just add two stops. And when you do a test strip in stops, the values will be equi-spaced, e.g. 2.0, 2.25, 2.5, 2.75, 3.0, 3.25, 3.5, 3.75. If you converted all of those to seconds, you'd get some really annoying numbers. It's also very easy to apply drydown correction; the software just needs to subtract a configured value, e.g. 0.08.

It also makes it easier to do stuff like grade changes when printing split-grade. My timer doesn't directly support that (i.e. it won't recompute the times for a grade change, or do a grade change while preserving a particular zone), but the use of stops to represent each exposure time makes it relatively simple for the user.
• 08-25-2011, 10:26 AM
Barry S
I appreciate this is a simple project to construct, but it would be helpful if you could post a schematic. Did I miss it? Thanks.
• 08-25-2011, 10:44 AM
Monito
Thanks. For reference, here is the other thread: http://www.apug.org/forums/forum43/9...top-timer.html

It seems that only the C++ code has been released. The page given the OP doesn't have a schematic or a parts list.
• 08-25-2011, 12:56 PM
polyglot
I haven't posted a schematic yet, sorry. However, there is literally nothing to do except connect the Arduino to the LCD and Keypad according to the pin-definitions in the source file. I will get around to drawing one soon that shows how to interface a solid-state or coil relay.

PS: new code is uploaded, it now does test-strip (differential exposures for each step) and test-tile (complete exposures for each step) generation. Always 8 steps, but you get to choose the base exposure and difference in stops between steps. Test strips are the classic approach we all know and test-tiles are how I prefer to do exposure testing. Tiles take a little longer to expose but you get the same part of the image visible in each step of the test so you can pinpoint exactly the exposure you need for a particular highlight or shadow for example.

You'll probably have to shift-reload the webpage, which now has some "WTF is an F/Stop timer" explanation and a link to a Gene Nocon interview.
• 08-25-2011, 01:41 PM
Monito
Quote:

Originally Posted by polyglot
I haven't posted a schematic yet, sorry. However, there is literally nothing to do except connect the Arduino to the LCD and Keypad according to the pin-definitions in the source file.

Perhaps I'm seeing things, but your video seems to show at least two medium sized red capacitors, an outboard chip, the LED display panel, some resistors, a transistor, an IC chip, ribbon cables, and at least a dozen individual wires connecting various things.

Perhaps such complex circuits are obvious to you and "literally nothing", but it certainly seems non-obvious to me.
• 08-25-2011, 05:19 PM
SMBooth
Quote:

Originally Posted by polyglot
Time = 2^stops. So 0 stops is 1s, 2 stops is 4s, 3.5 stops is 2^3.5 = 11.314s.

SNIP

Ok I understand, thanks
• 08-25-2011, 08:21 PM
polyglot
Quote:

Originally Posted by Monito
Perhaps I'm seeing things, but your video seems to show at least two medium sized red capacitors, an outboard chip, the LED display panel, some resistors, a transistor, an IC chip, ribbon cables, and at least a dozen individual wires connecting various things.

Perhaps such complex circuits are obvious to you and "literally nothing", but it certainly seems non-obvious to me.

They're all leftovers in the breadboard and not connected to or not necessary for the timer at this point. The transistor is driving the backlight LED but is not required for this small LCD; I was just being nice to the AVR pin because I used to have a much larger LCD attached to it with bright white backlighting. Likewise the resistors for the keypad (hidden under the keypad ribbon), they're not required at the moment either but I'm testing with them in order to start multiplexing some of the LCD and keypad data lines, which will save me 4 pins and allow me to put a rotary encoder on there to adjust exposures. Obviously once I do that, a schematic will be absolutely necessary.

So at this point, yes, you can really build it with zero external components except for the relay-driver circuit. That will change a little soon.
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