Printalyzer - Darkroom enlarging timer & exposure meter

[dkonigs]

This is a project I've been working on for a few months now, which I've discussed a bit among the context of this other thread:
https://www.photrio.com/forum/threads/using-an-enlarger-meter.180288/

I figured it was time for me to create a standalone thread for the project, and to share some blog posts I've written about the goals and progress.

Here's a blog post introducing the project:
http://hecgeek.blogspot.com/2020/11/introducing-printalyzer.html

And here's a newer blog post that talks about the current progress and status of the project:
http://hecgeek.blogspot.com/2020/12/printalyzer-project-update.html

 

[albada]

I read your blogs. Wow! Your Printalyzer is very promising. A few ideas that I can think of:

- The probe has a sensor hole, and that hole will cast a shadow on part of the photodiode when measuring away from the center of the image. I suggest raising the photodiode to be almost flush with the top. Darkroom Automation did that.
- Measurements might be more accurate if the probe is pointed toward the lens. To keep the sensor close to the easel, it would need to be at the bottom of a shallow cone. You could put a wire loop some distance above the sensor which would cast a shadow around the sensor, allowing the user to aim it accurately by centering the sensor within the shadow of the loop.
- Make the photodiode and associated circuitry sensitive. If the device can meter bright sky that created very high negative-density, then it can suggest a burn-time for such sky.
- If you are blocked by required government approvals, consider removing the timer function, turning this device into a smart meter. Then it can be powered by a separate already-approved off-the-shelf module that supplies a low voltage to your device.
- Consider labeling the buttons with words instead of symbols. That would allow the unit to be used without reading the manual. Symbols communicate little to a new user.
- Consider adding single-function buttons for common operations, such as "Select Paper", "Test Strip", "F-Stop Timing Mode", and "Clear Measurements". Alternatively, you can add soft-function buttons along the bottom of the display.

Good luck with it!
Mark Overton

 

[ic-racer]

Wow, that is truly amazing, I'm really impressed. I'm amazed at the resources available today. As it turn 2021 the darkroom timer/exposure meter I made in the early 1970s would be almost 50 years old. At the time it was the most sophisticated device I ever created, being my first INTEGRATED CIRCUIT project! Featuring the newly released 555 chip and a CDS cell!

 

[dkonigs]

- The probe has a sensor hole, and that hole will cast a shadow on part of the photodiode when measuring away from the center of the image. I suggest raising the photodiode to be almost flush with the top. Darkroom Automation did that.

When I was designing the meter probe, I believe I did some "back of the envelope" calculations on light angles to see if I'd have issues. I think I came out of that okay. I also recall this problem actually not being as bad as you'd think it would be. However, I should spend some time re-doing those calculations, and documenting the whole process, so I can experiment with different designs. One issue I have to contend with regardless, however, is that I can't elevate the sensor above the PCB without putting it on a daughterboard. That being said, making the enclosure as thin as possible above the sensor is another approach that I'm at least partially doing already.
For what its worth, I expect putting a transparent/translucent cover on top of the sensor hole will affect my readings. So I really need to start getting serious about that, to see what the data looks like.

Regardless, a huge point of my design was to make the meter probe "something I can muck with." Therefore, I fully expect to have to iterate on it once I start doing actual darkroom tests with real negatives.

- If you are blocked by required government approvals, consider removing the timer function, turning this device into a smart meter. Then it can be powered by a separate already-approved off-the-shelf module that supplies a low voltage to your device.

The thought has occurred to me, but I really still need to be able to actually control the enlarger and safelight to do what I want. If there was a 3rd party "off the shelf" box I could plug in to provide this function, I'd consider making a version that used it. Unfortunately, I haven't been able to find any good choices here.

- Consider labeling the buttons with words instead of symbols. That would allow the unit to be used without reading the manual. Symbols communicate little to a new user.

What's interesting with this is that RH uses symbols for the Analyser, but uses words for the StopClock. I'm not really set on the artwork yet, but my biggest hesitations with words is that they're harder to read (especially under darkroom conditions), make it harder to change functions, and you really can pick fairly obvious symbols for the most common features.

- Consider adding single-function buttons for common operations, such as "Select Paper", "Test Strip", "F-Stop Timing Mode", and "Clear Measurements". Alternatively, you can add soft-function buttons along the bottom of the display.

I'm actually doing this already. One of my biggest gripes about the RH product is needing to remember specific button combinations for certain features. I want to avoid that as much as possible. So yeah, I already have dedicated buttons for some of these. In places where I can't easily have a dedicated button, I can actually present the user with a clear text menu (something impossible on those circa-1996 units that only use 7-segment LCDs for their displays).
Another thing I included (though I'm not yet sure how effectively I'll be able to take advantage of this), is a few buttons that have embedded LEDs. The idea here is that I can have a visual indication of either what mode you're in, or what buttons you can push.

I should also mention that all of the LEDs on the panel of this device (both the ones embedded in buttons, and the ones surrounding the buttons for general illumination) are individually controllable. So while I currently don't have plans to leverage that too much, it may give me interesting options in the future. (Its great what you can do with modern special-purpose ICs. Why bother building some "simple" circuit to drive 10-14 LEDs with adjustable brightness when you can simply buy a 16-channel constant current LED driver chip with individual channel control for like $1 before quantity discount.)

 

[MattKing]

- Consider labeling the buttons with words instead of symbols. That would allow the unit to be used without reading the manual. Symbols communicate little to a new user.

What's interesting with this is that RH uses symbols for the Analyser, but uses words for the StopClock. I'm not really set on the artwork yet, but my biggest hesitations with words is that they're harder to read (especially under darkroom conditions), make it harder to change functions, and you really can pick fairly obvious symbols for the most common features.

You could consider charts that show the word - symbol equivalencies, sized to fit on the blank part of the cabinet.
If they were available in several languages, you could expand your market!
Produce them as fridge magnets, and they would be perfect!

 

[Patrick Robert James]

Definitely interested in this. i'd settle for just a plain meter. Don't really need the timer.

 

[gijsbert]

Just the sensor with bluetooth and/or 3.5mm plug to interface to raspberrypi or mobile phone would be very useful too.

 

[MattKing]

Definitely interested in this. i'd settle for just a plain meter. Don't really need the timer.

And as I could use a timer, I would be most interested in that, with .
The two features I didn't see (but may have missed) are:
1) a safelight outlet; and
2) a common plug for an easily available foot switch.

 

[dkonigs]

And as I could use a timer, I would be most interested in that, with .
The two features I didn't see (but may have missed) are:
1) a safelight outlet; and
2) a common plug for an easily available foot switch.

It has both of those. You'll see the ports if you look closely at the panels on the front and rear of the unit.

 

[MattKing]

It has both of those. You'll see the ports if you look closely at the panels on the front and rear of the unit.

Thanks. I missed the foot switch port, and hadn't noticed the photo of the back. I paid more attention to the written feature list.

 

[albada]

Your resourcefulness surprises me. How did you know that a company even exists that could make the box and control panel? I would have bought a project-box somewhere and started cutting and drilling it myself. And other niceties that you got from somewhere; I wouldn't know where to start.
BTW, did you solder those surface-mount parts yourself? I can handle an SM resistor and such, but a 40-pin IC?
Finally, Darkroom Automation resells a nice metal footswitch made by somebody else. I can tell you the info on it if you're interested.
Mark Overton

 

[radiant]

This looking really good.

Please add "auxillary" port for extending the hardware, for example to external LED control. I would add a "multi-purpose" port with UART. UART digital pins could be used to control for example WS2812 leds too directly. Maybe D9 connector would be most usable? No need for +12/-12V levels. maybe make it 5V compatible (WS2812). The RX/TX lines could be also used directly to run PWM if anyone is using B+G leds.

 

[dkonigs]

Your resourcefulness surprises me. How did you know that a company even exists that could make the box and control panel? I would have bought a project-box somewhere and started cutting and drilling it myself. And other niceties that you got from somewhere; I wouldn't know where to start.
BTW, did you solder those surface-mount parts yourself? I can handle an SM resistor and such, but a 40-pin IC?
Finally, Darkroom Automation resells a nice metal footswitch made by somebody else. I can tell you the info on it if you're interested.
Mark Overton

I've been poking around for a while, chatting with friends and scouring electronics forums, and honestly there aren't many choices out there on companies that can (easily) build cases for you like this. In the past, I'd have 3D printed an enclosure for a project, but this thing is a bit too large for that to be practical. I've actually stumbled across two different companies that are useful in this area: Front Panel Express and Protocase. Both have design software you can download to make things they can build for you. I used the former here. The latter is probably a lot cheaper if I were making a larger quantity, but similar in price if I'm only making one or two.

Yes, I soldered the surface-mount parts myself. I had been afraid of surface-mount stuff for years, but finally overcame that fear and fully embraced it on a previous project. These days, if you want to build anything that uses modern components, you really have no choice. The process is a little different, and requires some tools you wouldn't have had in the past, but not too bad once you get used to it. You basically use a stencil to smear solder paste on the board, place all the parts with tweezers under a stereo microscope, and then bake in a reflow oven. (Of course you still want a soldering iron and a hot air gun to fix things or do one-offs.)

As far as footswitches go... I found out that the "premium" footswitch that RH Designs sells comes from Herga, so I went and got myself one of those. (Though the one I ended up with has a cable that's a bit too thick, so anything I use long term should probably have a custom-fitted thinner cable.) I would be curious to learn what Darkroom Automation chose for their footswitch.

 

[dkonigs]

This looking really good.

Please add "auxillary" port for extending the hardware, for example to external LED control. I would add a "multi-purpose" port with UART. UART digital pins could be used to control for example WS2812 leds too directly. Maybe D9 connector would be most usable? No need for +12/-12V levels. maybe make it 5V compatible (WS2812). The RX/TX lines could be also used directly to run PWM if anyone is using B+G leds.

I've seen a lot of mention of ideas like this, and it would be a good idea to include something in a future revision. However, I might need to make the device bigger to have space on the rear panel. The main issue, though, is that I'd first want to know exactly what would be getting connected this way. In the world of LED-based heads, there are a few commercial products (all with their own proprietary controllers) and probably a bunch of DIY solutions. They likely all have different control interfaces, and I don't really know what any of them look like. (And right now, I don't have anything spare I could "just make a UART port out of", but I do have some spare pins that could do SPI or be used as GPIO.)

 

[radiant]

LED-based heads, there are a few commercial products (all with their own proprietary controllers) and probably a bunch of DIY solutions.

Commercial systems you can count out for the reasons you explained. Maybe UART is too much but for most of DIY LED setups I think three PWM outputs would be enough. And for WS2812 one digital pin is enough.

If you need to save space, maybe 4-pin 3.5mm plug (TRRS) would be enough for this. GND+RED+BLUE+GREEN ..

 

[dkonigs]

Speaking of LED heads, they do present one interesting side-project that could be done with the help of the right sensor in this thing's meter probe... Actually calibrating the channel brightness settings so that you can directly match the common contrast grades and/or dichroic filter settings.

Of course the moment I do go down this rabbit hole of handling LEDs heads, it starts to make more sense to decouple "power control" from the rest of the device. If I do that, then I could also make the rest of the device into something entirely "low DC voltage" and requiring of fewer certifications to sell. (You'd still need the ability to switch mains power, but that could be left as a DIY project for the user with some reference designs.) The main downside of doing this, of course, is it then becomes a lot more complex to set the thing up and you'd have a nasty cable/device mess that I'm really trying to avoid. (Just looking at all the boxes and D-sub connectors needed to connect the Heiland stuff together kinda makes me cringe a bit.) FWIW, it does seem like the Maya Darkroom Timer project has its power controller as a separate unit.

In any case, as I've alluded to before, the biggest issue with LED heads is that they're not a "known quantity" for controlling. If there was some known set of "standard" controllers or DIY designs that everyone used, that I could work against, it would make this a lot simpler. (Even just saying "three PWM outputs" or "one or two digital pins" doesn't mean much if I don't know the voltage levels, frequencies, circuit protection needs, additional control/feedback signals that might exist, etc.)

 

[MattKing]

A replacement source of reliable bluetooth controlling software might allow Modern Enlarger Lamps Model 3 to come back into production: http://www.modernenlargerlamps.com/Modern_Enlarger_Lamps/Model_3.html

 

[gijsbert]

I built my own timer with a raspberrypi zero with no box, indeed a bit of a wire mess, you are working on a very nice solution!

After looking at electronic relay components, I went with this https://www.buyapi.ca/product/iot-power-relay/ to do the power switching for the enlarger (bulb) and safe light. It has 4 power sockets, 1 always on (powers the raspberrypi, via usb charger), 1 normally on (safe light), 2 normally off (enlarger, spare), and 1 signal line to reverse the on/off sockets. It's more limited than generic banks of relays but my electronic skills are minimal so I was happy I found this product.

 

[dkonigs]

I built my own timer with a raspberrypi zero with no box, indeed a bit of a wire mess, you are working on a very nice solution!

After looking at electronic relay components, I went with this https://www.buyapi.ca/product/iot-power-relay/ to do the power switching for the enlarger (bulb) and safe light. It has 4 power sockets, 1 always on (powers the raspberrypi, via usb charger), 1 normally on (safe light), 2 normally off (enlarger, spare), and 1 signal line to reverse the on/off sockets. It's more limited than generic banks of relays but my electronic skills are minimal so I was happy I found this product.

I'm well aware of this product. The problem is that its the only product I can find anywhere (unless you include expensive industrial PDUs) that could let me "outsource" enlarger power control. Also, it has a few shortcomings that are probably showstoppers for my use case:

• It only has one independently controllable outlet (I really need to control the enlarger and safelight separately), so I'd need two of them.
  
• It is kinda big and clunky, so having two of them dangling off the back of my device wouldn't be so nice.
• Its completely useless for anyone who doesn't use US power plugs.

That being said, once my device is essentially complete (I still have a lot more work to do on the firmware side, and maybe a bit on the sensor side too), I am open to making the power control portion a bit more "modular."

 

[ic-racer]

If there was some known set of "standard" controllers or DIY designs that everyone used, that I could work against, it would make this a lot simpler.

I have been collecting info on home-made LED B&W printing heads for many years. I agree; each project essentially re-invents the wheel. However, I also collect commercially produced schematics and enlargers and have repaired or have knowledge of almost ten different 'regulated' incandescent enlarger power supplies. Similarly, they are all different. Even Omega had at least 3 totally different solutions. I suspect each enlarger company hired a design firm to come up with a regulating circuit; all independently. The circuit designs are all over the place.

 

[ic-racer]

I'm not the one to do it but I'd support an internet "LED Enlarger Head Collaborative Design" with some Arduino based components to make, not only 'open source' software but also 'open source' building block PC boards.

I know there are probably many examples of collaborative projects like this but the one I'm most familiar with is the ECONOWAVE audiophile speaker design collaborative here: https://audiokarma.org/forums/index...esign-collaborative-econowave-speaker.150939/

 

[albada]

[...]the biggest issue with LED heads is that they're not a "known quantity" for controlling. If there was some known set of "standard" controllers or DIY designs that everyone used[...]

Set that standard yourself. That is, define an interface, and let others adapt to it. If your interface is simple, many of us with DIY heads could easily adapt to it. For the simplest interface, I can think of two possibilities:

1. PWM using 5 volts (traditional TTL-levels).
2. PWM using resistance (i.e, open/shorted).

The Meanwell LDD-H and LDD-L series of LED-drivers use 5v. The BuckBlock uses resistive PWM-control. If you provide 5v, anyone can easily convert your signals into resistances by running each signal through a 10K resistor connected to the base of a 2N3904 (or two if inversion is needed). Anyway, look at the popular drivers and select a PWM-interface that makes life easy for everyone.
Mark Overton

 

[albada]

Here's the info on the foot-switch sold by Darkroom Automation:

CONNTROL 892-1990-33
My own searching shows that Conntrol is here: https://conntrol.com/shop/
My foot-switch is series 892, model 892-1990-33, which sells for $24.01.
It's all-steel and looks well-made, but their web-site says it's for "light-duty" use.
Their series 862 is called "ergonomic" because they are hinged at the user's heel, and is about the same price as series 892.
Mark Overton

 

[dkonigs]

Here's the info on the foot-switch sold by Darkroom Automation:

CONNTROL 892-1990-33
My own searching shows that Conntrol is here: https://conntrol.com/shop/
My foot-switch is series 892, model 892-1990-33, which sells for $24.01.
It's all-steel and looks well-made, but their web-site says it's for "light-duty" use.
Their series 862 is called "ergonomic" because they are hinged at the user's heel, and is about the same price as series 892.
Mark Overton

Thanks for the info! Those footswitches may be ideal "out of the box" solutions, since that specific version actually comes with the exact sort of plug I'm using in my project and a low enough current rating that the cable is hopefully slim as well.
(Actually finding those Herga footswitches with a low current rating, and hence a slim cable, seems difficult. My current "test" footswitch is a Herga 6050 that has a 6A rating and a cable that's a little bit too thick. Still managed to get the connector onto the end of it, but its not the most practical setup.)

 

[albada]

Thanks for the info! Those footswitches may be ideal "out of the box" solutions, since that specific version actually comes with the exact sort of plug I'm using in my project and a low enough current rating that the cable is hopefully slim as well.
(Actually finding those Herga footswitches with a low current rating, and hence a slim cable, seems difficult. My current "test" footswitch is a Herga 6050 that has a 6A rating and a cable that's a little bit too thick. Still managed to get the connector onto the end of it, but its not the most practical setup.)

A micrometer tells me the wire between my foot-switch and plug is .15 inches (3.8 mm) thick. It's 6 feet long, and has good strain-reliefs on both ends.