Printalyzer Densitometer - A compact budget-friendly densitometer project

[Steve Goldstein]

One thing you might consider pursuing in the future is a UV version for people working with alt processes. I understand that both the source and detector are more challenging that for visible light, but it might be an easier problem to solve than a full-color version, and it might actually garner better sales.

Just a thought, it's easy to come up with ways to use up someone else's time

 

[dkonigs]

One thing you might consider pursuing in the future is a UV version for people working with alt processes.

That absolutely is something I'm considering for a future version of the device, but not for the initial version. While such a version isn't inherently more complicated, I would need to:

• Choose a spectrum for which calibration materials are available (and perhaps existing equipment to compare against. (This could either be ISO 5-3 Type 2, Status A/M Blue, or whatever X-Rite's UV densitometers measure.)
• Use a different sensor with sufficient sensitivity in the right portion of the spectrum (maybe different LEDs, but that depends on specifics)
  
• Use different filter materials in the sensor head

The other issue is that I'd need to settle on a single spectrum standard that would be acceptable for both reflection and transmission, since I use the same sensor setup for both.

Another option would be to build a version with the AS7341 sensor I've mentioned elsewhere. With that sensor (and a simple IR-only cut filter) I could probably handle roughly any spectrum choice without changing hardware. The downside it that I'd only be able to target that spectrum choice roughly, so precisely matching existing densitometers would be far easier said than done.

In any case, I'm not going to distract myself with this idea too much in the short term.

 

[Steve Goldstein]

Glad to hear you’re considering it. Speaking from my day-job life as an electrical engineer you’re asking all the right questions and clearly understand your priorities. I’ve seen too many projects, including some of my own when I was a baby engineer, get derailed by a lack of focus.

To be honest, I’m not sure there’s much photographic value in a UV reflection unit. I would think the dominant use case would be measuring the transmission of negatives for UV-sensitive printing processes. That might make the task a bit easier when and if you finally get to it.

It might also prove easier to have separate units for visible and UV that share the same external hardware but differ internally.

Absolute accuracy is great if you can do it affordably but it may not be a necessity. Making sure each unit is individually stable (thermally and long-term) and repeatable is critical. But if I’m calibrating MY process in MY darkroom it doesn’t really matter to me if my unit and yours don’t read identically under identical conditions.

But don’t let me distract you too much. Like I said, I’m good at finding ways to help other people use up their time. I do really want to see this come to life. A small, simple, easy-to-use transmission densitometer would be a real boon.

 

[dkonigs]

To be honest, I’m not sure there’s much photographic value in a UV reflection unit. I would think the dominant use case would be measuring the transmission of negatives for UV-sensitive printing processes. That might make the task a bit easier when and if you finally get to it.

Unfortunately going transmission-only actually doesn't make this any easier. The number of components I'd be able to omit by doing that is minuscule. (However going reflection-only, like some of my earlier concepts, would be a rather large savings since I could omit half the enclosure and a fair bit of mechanics.)

It might also prove easier to have separate units for visible and UV that share the same external hardware but differ internally.

This is exactly the approach I would take. Some of my earlier "research prototypes" (as detailed at the tail end of the Printalyzer Meter/Timer thread) were actually built in a variety of sensor/LED combinations (in the same enclosure) to test things out. No reason I couldn't do the same with the full-up device.

But if I’m calibrating MY process in MY darkroom it doesn’t really matter to me if my unit and yours don’t read identically under identical conditions.

Sorry, but the "you your yours" approach to calibration is kinda one of my pet peaves Even if the "standard" I use isn't something that comes with an official NIST certificate, there should still be one. At the very least, so that you don't have to throw out all your data if you switch devices, or need to recalibrate for some reason.
However, calibration is not (and should not be) a factory-only thing. So my device will come with calibration references with known values you can re-run calibration on, or you can even re-run calibration with your own references if you'd like.

(My biggest "gripe" with Heiland's TRD-2 is that they do not provide any way for the end-user to recalibrate the device, unlike every other "real" densitometer.)

A small, simple, easy-to-use transmission densitometer would be a real boon.

Yeah, I'm really looking forward to bringing this project to fruition. I just hope certifications and electronics supply chain issues (that have been all over the news) don't end up dragging things out for too long. (I might start ordering some parts in quantity a bit prematurely just to hedge my bets on that one, but we'll see.)

 

[dkonigs]

So, a fair bit has happened on this project since my last post. Basically, I'm moving forward with the plans to turn this into an actual product!

First, I went ahead and actually set up the company I'm going to be using for bringing all of these projects to market:


I also setup a website and relevant social feeds:
https://www.dektronics.com/
https://www.twitter.com/dektronics
https://www.instagram.com/dektronics/

Then I began to start ordering the parts I'm going to need for the first production batch. Not everything just yet, but the things that have longer lead times and/or will be difficult to get on-demand during the current global electronics component shortage.

During this time, I also continued to work on the enclosure design and also made one more pass at giving Multi-Jet Fusion (MJF) a chance. I'm pleased to say that I found a small MJF vendor who can actually build my models with accurate and repeatable dimensions!
(As a recap, I discovered that when the 3D printing operator is a large company that doesn't care about you as an individual customer, SLS gets much better accuracy and repeatability than MJF. However, when the operator does care about you, MJF works very well.)

From here on out, my plan is to have the final pre-production prototype ready sometime in January/February. After this point, I'll begin sending out a few evaluation units for promotional purposes and launch a Kickstarter. The goal of the Kickstarter will be to help lock in the initial production batch, build interest and a community, and to help promote the project further.

Finally, here's a somewhat casual video I threw together today to introduce the project:

(Don't worry, I still plan to make a "proper" video to accompany the product's official announcement.)

 

[StrangestStranger]

Hello Derek,
I've been following this thread and very much am interested in your product. Please be sure to post your Kickstarter link here when you do launch it. I will totally back your product. Thanks for being a great innovator!

 

[Mr Bill]

Cool project, and I wish you great success.

A little late to be saying this now, but I just watched your video. In the real world of reflection densitometry there's a lot of value to being able to read different parts of a largish print (without cutting it up).

So for future use it might be worth having a dismountable reading head or possibly a hinge that could swing wide open. For something like this one also needs a guide to know exactly where they're reading. Macbeth reflective units had a hinged base with a targeting grid built in, which worked pretty good. An alternate method is used by Xrite in their i1 (Eye-one) handheld spectrophotometer units (typically used when making ICC profiles). They have a couple different plastic bases, where the base is held in place, then the reading head is set into the base for a reading.

As a note, when used to make printer profiles, reading hundreds of patches, the i1 unit slides along a slot, where something like 10 or 20 patches can be read in a "swipe." Of course, this gets a lot more complicated - the instrument relies on a computer data file to know what's coming in order to do some error checking, etc. Even so, things can be a bit flaky - operator has to develop a certain swipe technique. Anyway, I thought it might be worth making you aware of some of these ideas.

Again, wishing you success!

 

[albada]

Count me in!

Mark Overton

 

[koraks]

Congratulations on the new venture! May your new product introductions be many and successful

 

[dkonigs]

So I've been semi-regularly posting videos to the Dektronics YouTube Channel, and also posting occasional project updates on the various related social media channels.

The latest video shows a montage of actually assembling one of these devices (every step after putting the PCB itself together), and I figured I might as well share it here.

Pre-Production Prototype Assembly


This is the second of two units of the "final" pre-production design. The next step will be to build out the rest of the batch (up to 8 more units) to get me through various forms of testing and evaluation. Once that's all settled*, I'll finally be ready to start producing these things for real.

(* And I've written the manual, finalized the labeling/processes for calibration references, added more polish to the firmware and desktop software, etc, etc.)

 

[ic-racer]

Impressive!! Anxious to read reviews.

 

[albada]

Impressive! Anxious to get one, as I've been taking many measurements.
How do you plan to calibrate it?

 

[dkonigs]

Impressive! Anxious to get one, as I've been taking many measurements.
How do you plan to calibrate it?

So calibrating it involves a couple of steps, which can be divided into "factory" and "user" calibration, or as I often refer to them, "sensor" and "target".

The "sensor" calibration involves two parts:

1. An automated process that takes measurements across several pairs of sensor ADC gain settings, keeping the other conditions constant, as a way of putting concrete numbers to those settings. (e.g. low=1x, medium=24x, high=400x, etc.. The datasheet gives a range, but I'd like to pin down an actual number so I can compare readings from different gain settings more confidently.)
2. A more manual "slope" calibration process, where I measure an entire calibrated step wedge and run some calculations to determine the sensor's response curve across its range. The coefficients generated by this process so not appear to vary substantially from device to device, so I'll likely end up doing them on a batch level.

The "target" calibration process, which is what most densitometer users are accustomed to. I'll also provide materials with the device so you can re-do it whenever you'd like. It basically consists of:

1. A reflection target with a series of patches at known densities, which you measure at two points
2. A transmission target with a series of patches at known densities, where you measure with nothing under the sensor and then you measure a specific dark patch.

 

[albada]

Sensible calibration procedures.
BTW, I didn't know you had a Youtube channel, and I just watched your video about microcontrollers. Congratulations on obtaining them! Yeah, I see many "0 - immediate" in both Mouser and Digikey. Ugh.

 

[dkonigs]

Its been a while since my last post, and while I've been posting plenty on the Dektronics social media feeds and YouTube channel, I figured I should post another update here.

I've now built several more of the pre-production units, and you can see here:

The first two on the right are for my own development purposes, the next two were recently used for EMC compliance testing, and the last two on the left are the first ones I'm planning to send out to actual test users in the near future.

Yes, last week I actually took the Printalyzer Densitometer to an EMC compliance testing lab! Everything passed, so as soon as I get the report back I'll be updating the labels and documentation to reflect all the regulatory language. This is the last major piece of "red tape" before I can start publicly distributing the device.

Here's short video I made where I talk about the various bits of product testing I've gone through over the past month:


From here on out, my plans are to build and distribute a couple more evaluation units, and then use the feedback to polish the device software and documentation. From there, I'll start gearing up to actually build production units.

 

[tih]

Looking good! Don't forget to let us know here when the Kickstarter campaign launches!

 

[albada]

Congratulations! I marvel at the breadth of your talents. You are good at electronics, software, mechanics, and now EMC certification. Such a densitometer is needed, and you are clearly the man for the job. BTW, I've seen ESD zappers being used. They give me respect for TVS diodes. Did you use many TVS diodes? Did you cover any interior surface with sheet metal in order to pass EMC or ESD?

Mark Overton

 

[RalphLambrecht]

Since I've finally managed to write a sufficiently-detailed blog post on the project, I figured it was time to fork it off into its own discussion thread.

View attachment 280473

Here's the blog post:
http://hecgeek.blogspot.com/2021/07/the-printalyzer-densitometer-project.html
(More pictures, including ones of the latest prototype, are in the blog post.)

Here's where I've previously been discussing it:
https://www.photrio.com/forum/threa...mer-exposure-meter.180377/page-5#post-2409172

Here's where I'm posting the design artifacts (schematics, source code, 3D models, etc) for the project:
https://github.com/dkonigsberg/printalyzer-densitometer

For now I'm focusing on measuring in the "Visual" (B&W) spectrum. As much as I'd love to also do color, there are some technical limitations in getting accurate readings at the right wavelengths for that on a budget. (Though it'll continue to be a back-burner idea I may tinker with from time to time.)

Right now I'm thinking that this project may be something I attempt to bring to market a lot sooner than my main Printalyzer Timer/Meter project, because there are far fewer hurdles. Its also likely to be a good "test project" to get my feet wet with the whole process of actually doing something like that. I have no idea what my cost target will be yet, but I know what I'm competing against. (Heiland TRD-2 and used 80's/90's era devices on eBay) However, I may need to wait until the "great microchip shortage of 2021" starts to subside before I can build more than a handful of prototypes.

despite the cost I will always recommend the Heiland densitometer.The quality is worth it.

 

[dkonigs]

Congratulations! I marvel at the breadth of your talents. You are good at electronics, software, mechanics, and now EMC certification. Such a densitometer is needed, and you are clearly the man for the job. BTW, I've seen ESD zappers being used. They give me respect for TVS diodes. Did you use many TVS diodes? Did you cover any interior surface with sheet metal in order to pass EMC or ESD?

Mark Overton

I actually used plenty of TVS diodes, just to be safe. However I'm not sure if they ended up being useful. In the ESD zapper test, nothing on the device even conducted in the first place... except the shield of the USB connector, and then only sometimes. I think the general lack of exposed metal connected to anything helped there.

None of the interior surfaces around the main circuit board were covered with metal, but it was a 4-layer board. Also, because its so low power, I used a linear regulator. I think that all helped, as the device was pretty quiet in terms of emissions.

 

[dkonigs]

I know its been quite some time since my last post on this thread. I've been providing regular updates via Instagram and Twitter, and posting the occasional YouTube video.

However, I'm finally getting really close to actually going into production, so I'd like to share my last two update videos here:





The short version is that basically all the hardware has been ordered, most of it has arrived, and I should have the parts to finally start assembling production devices during this week or next.

With any luck, that means I could finally start having densitometers ready for sale sometime in October.

 

[albada]

I'm glad you are putting this in production.
When it's available for sale, please post here.

 

[BHuij]

This looks spectacular. Can't wait to either buy or make one. Any plans to offer kits that include the PCB and components to populate it for those of us who would be happy do our own soldering/flashing/3D printing/assembly?

 

[koraks]

do our own soldering

I don't think the market for a DIY kit like this involving SMD soldering is going to be very big. I wouldn't be put off by it, but the first time you run into the challenge of getting a tiny QFN package onto a PCB, it tends to be a bit of a head-scratcher.

 

[BHuij]

I don't think the market for a DIY kit like this involving SMD soldering is going to be very big. I wouldn't be put off by it, but the first time you run into the challenge of getting a tiny QFN package onto a PCB, it tends to be a bit of a head-scratcher.

Fair point, and now realizing that this isn't all just standard through-hole stuff, maybe the kit that would make more sense is a fully populated PCB with the other non-printable components. I mostly just feel confident doing my own printing and assembly, and flashing firmware shouldn't be bad either if it can be done over USB.

 

[koraks]

flashing firmware shouldn't be bad either if it can be done over USB

Don't think so, sorry. Microcontrollers generally don't come with pre-installed bootloaders unless you order a couple of thousand units and pay for them to be preflashed. The STM32 likely used in this design can easily be programmed with an stlink device though; Chinese clones aren't expensive. What's the added value of this though?

The added value of the kind of kit you're describing is mostly to allow people to fashion their own housing around it. Being able to say "look I made this", I guess. In the case of this device, this mostly brings all kinds of opportunities for compromising the optical design, specifically the probe assembly.

Some things are really just best accepted as they are; I think this here is a good example.