# Open source f/stop enlarger timer released

Discussion in 'Darkroom Equipment' started by polyglot, Aug 23, 2011.

1. ### polyglotMember

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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.

2. ### paul ronMember

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3. ### SMBoothSubscriber

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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.

4. ### polyglotMember

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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.

5. ### Barry SMember

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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.

6. ### MonitoMember

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7. ### polyglotMember

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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.

8. ### MonitoMember

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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.

9. ### SMBoothSubscriber

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Ok I understand, thanks

10. ### polyglotMember

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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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11. ### Barry SMember

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I (hopefully) ordered everything I need today:

Arduino Duo \$20
4x4 keypad (tough to find one with letters!) \$15
16x2 red LCD \$8
Power switch tail 2 \$30

I found everything (except the Power switch tail 2) on ebay. It's all being shipped from China, so I figure I'll have everything in about 10 days. I should be able to scrounge some sort of case, so les than \$80 shipped for everything isn't too bad.

12. ### polyglotMember

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Nice to see someone is going to try this! I am currently on holiday (on Budapest airport wifi right now, transiting Prague-St Petersburg) and back in October so can help you out in earnest then.

I take it you mean an Uno? I'm not aware of an Arduino Duo.

In related matters, I've drawn up a schematic and PCB in KiCad and will be sending it off for manufacturing in October. I'll put the design files on the webpage then too, and make the spare PCBs (if error-free) from the prototype run available.

I've also added (due to request from an lfpf-er) a rotary encoder for exposure changes. It's completely optional in the build though; just leave it out if you don't want it.

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15. ### Barry SMember

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Sorry, it was indeed an Arduino Uno that I ordered. Just a temporary moment of dyslexia after seeing all the versions offered online. Not sure I understand the function of the rotary encoder--is it to adjust the base exposure?

16. ### polyglotMember

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Rotary encoder is currently set to change any exposure you're looking at in the Edit menu. I'll also make it so that when turned in the Exec menu it will change the base.

17. ### MonitoMember

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I think the operation of device will be a bit tricky the first few times, but I can see the workflow logic behind it.

I think it would work very well in practice after the first session using it.

[on edit:] Hmm, the post I responded to, but did not quote, seems have been withdrawn.

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18. ### paul ronMember

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Still no schematics?

.

19. ### Lee LMember

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October is next month, which gives him about 3 to 7+ weeks. Why would he want to release an untested schematic and deal with all the attendant headaches?

Lee

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Because he wants to follow in Bill Gates' footsteps? Or doesn't.

In the early days of the 'home computer' era in the mid to late 70's many companies operated with [and openly endorsed] the 'thousand engineers principle': they didn't bother to debug the product; instead they sent it out and let the customers get the bugs out. They then incorporated the changes that came back to them in irate letters [paper - few had ARPANET access] "Hey you idiots - pin 3 of IC 12 needs a 1K pullup, and you mislabeled the connections on J3!...." Billy G. was working on software for the Altair 'computer' at the time - an early adopter of the thousand engineers principle.

Just think of all the blue-screen-of-deaths and virus attacks that would have been avoided if Billy had finished his education.

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21. ### Barry SMember

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It's called an open source project. William is graciously sharing a personal project with the thought that others may find it useful as-is or with modification. There is no financial benefit involved. I appreciate his work and look forward to experimenting with the arduino.

22. ### Tim GrayMember

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Cool little project. I should do something with the arduino I have sitting on my window sill.

23. ### polyglotMember

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Hi guys,

I'm currently sitting in a combo bar/cafe/laundromat in St Petersburg drinking vodka and waiting for the dryer while the schematic is on my PC in Adelaide. I won't be home 'til October 3 and will have well over 100 rolls to process when I get there, so don't expect to see the schematic until at least 4-5 weeks from now. When posted (along with the additional rotary encoder source), it will be GPL of course. It may well have issues too but nothing that should be insurmountable.

If you're impatient, you can build it on a breadboard with no additional components and using the pin definitions in the source currently on my website.

I'm gonna go shoot some grubby decrepit buildings now; I think the street lights are nearly on.

24. ### polyglotMember

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OK, update time.

I've designed a PCB, paid for manufacturing and I will probably send the design off this weekend. In theory that will get me 10 PCBs so I will have about 9 of them for sale for about \$8 each if they work. I want to get the finished PCBs back and tested before I post the files on my website so given manufacturing turnaround times plus the fact that I'm 15% of the way through scanning 100 rolls from my holiday (some photos from the night of my previous post) means it will be well into November before you see much. If you're keen to get started, I can email you a PNG of the schematic and some new source code - PM me.

For prototyping purposes I just used a breadboard as you can see in the video. If you don't want to buy a PCB, you can easily construct it on a "prototype shield" (eBay). For a box, I would recommend a rectangular ABS or Al case and I'm using this one (99x125x40mm), which is about as small as you can go and have it all fit.

25. ### Tim GrayMember

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Sounds good. I might be interested in a PCB...

26. ### paul ronMember

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OK so you prototyped it and it's working so how about the shematics so others with electronics experiance can see if it needs improvement or perhaps breadboard it themselves? Why the mystery? This thread is older than dirt.

Is this your schematic for the project or one like it?

http://www.brodie-tyrrell.org/fstoptimer/source/

I can't open the other files, what are you reading em with?

.

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