Fun with C# Strings: Interpolation and Verbatim

Relating to my adventures exploring iconography, this UWP application exercise also managed to add some novelty to a foundational concept: strings. Strings of characters to represent human readable text is a basic part of computer programming. Our very first “Hello World” program would use them… for the “Hello World” is itself a string! Even if someone learning programming had not yet covered the concept of strings, they use it right from the start. As such a fundamental building block, I had no reason to expect to find anything interesting or novel when I wrote C# code. It looks like C, so I assumed all strings behaved like C.

I was surprised to learn my assumption was wrong: there are some little handy syntactic shortcuts available in a C# program. Nothing that can’t be done some other way in the language and certainly nothing earth shattering, but nifty little tools all the same. I was most fascinated by the special characters.

The first one is $, the string interpolation prefix. I first came across it in a sample program that made generating some text output more succinct. It allows us to put variable names inline with the text and some tool in the compilation chain will handle the details of interpreting variable values as text and build the string for display. It definitely made the sample code easier to read, and can be nice in my own programs as well. It made code for my own simple logger easier to read. There is some minor security concern here as automatic interpolation risk introducing unexpected behavior, but at least for small play projects I’m not concerned.

The other special character is @, call the verbatim identifier. It disables almost all string processing for escape sequences, making it easy to use strings that have file paths: we no longer need to worry about the slashes accidentally becoming an escape character. It’s not something terribly common in my projects, but I do have to deal with paths and when I do so in C# this is going to reduce a lot of annoyance. And in direct contrast to interpolation, verbatim may actually cut down on security attack surface by making sure nothing unexpected can occur with escape sequences by eliminating the behavior completely. More tools in the toolbox is always good.

Icon Fun with Segoe MDL2

For my recently completed test program, I wanted arrows to indicate motion along X/Y/Z axis. I also wanted a nice icon to indicate the button for homing operations, plus a few other practical iconography. Thankfully they are easily available to UWP applications via Segoe MDL2.

One of the deepest memories from my early exposure to a graphical desktop environment is the novelty of vector fonts. And more specifically, fonts that are filled with fun decorative elements like dingbat. I remember a time when such vector fonts were intellectual property that need to be purchased like software, so without a business need, I couldn’t justify buying my own novelty font.

The first one I had impression of being freely available and didn’t quickly disappear was Webdings, a font that Microsoft started bundling with Windows sometime around the Windows 98 timeframe. I no longer remember if earlier versions of Windows come bundled with their own novelty fonts, but I have fond memories of spending far too much time scrolling through my Webdings options.

Times have moved on, and so have typefaces and iconography. For their UWP application platform, Microsoft provided an accompanying resource for Fluent Design icons called Segoe MDL2. And again, I had a lot of fun scrolling through that page to see my options.

I was initially surprised to see many battery icons, but in hindsight it made sense as something important for creating UI on portable computing devices. There were several variants for battery styline. Including vertical and horizontal orientations and charging, not charging, or battery saver. And each style had ten levels to indicate battery level 10% apart. Some of the code point layouts were a little odd. For example, Battery0 (0xE850) through Battery9 (0xE859) were adjacent to each other, but a full Battery10 was some distance away at 0xE83F. I don’t know why, but it adds an unnecessary step to convert a battery percentage value to a corresponding icon in Segoe MDL2.

The one that made me laugh out loud? 0xEBE8, a bug.

First Project Prototype Has Poor Precision

I’ve been bringing pieces together to build a machine to take distance measurements visually, with the primary motivation of measuring dimensions of circuit board features. Mechanically the machine is the three-axis motion control of a retired 3D printer, with a webcam sitting where the print nozzle used to be. It is controlled from a PC attached via USB, running software that I wrote as an exercise to learn UWP development. Once I figured out enough of UWP layout engine, I could put some user interface controls and take the thing on its first test drive.

Verdict: The idea has promise, but this first draft implementation is a bucket of fail.

For the first test, I taped a Digi-Key PCB ruler onto the Y-axis carriage where the print bed used to be installed. The ruler has clearly labeled dimensions on board representative of components on a circuit board. The first and easiest test is to make sure my movement distances match the ruler distance and this machine flunked its first test.

I have added a little circle in the middle of the camera field of view to serve as reference. I placed that circle at the 10 cm mark and commanded a move of 1 cm along the negative X axis. I expect the little circle to sit above the 9 cm mark as a result, but it is actually sitting at roughly 8.95 cm, a distance of 1.05 cm and roughly 5% longer than expected.

Camera control test 8.95mm

The first hypothesis is that this is an effect of the camera’s USB cable tugging on the camera as the print carriage moved, changing the viewing angle. It is, after all, merely held by tape on this first draft. So I repeated the experiment along the Y axis, which does not move the camera carriage and would eliminate flexible tape as a variable. Again I see a 5-6% overshoot.

When two measurement tools disagree, bring in a third opinion to break the tie. I pulled out my digital caliper and measured the ruler markings and they match, indicating the problem is indeed with the printer mechanicals. For whatever reason, this motion control carriage is moving further than commanded. Perhaps the belts had stretched out? Whatever the reason, this behavior could very well be why the printer was retired. I think I can compensate by changing the steps-per-millimeter setting in printer firmware, all I need is a precise measurement of actual movement.

Which brings up the other half of my problem: I can only get plus or minus half a millimeter precision with this webcam configuration. I can’t bring the camera any closer to the workpiece, because this webcam’s autofocus fails to focus at such close ranges.

I see two paths forward to address the optical precision shortcomings:

  1. Use another camera, such as a “USB microscope”. Most of the cheap ones are basically the electronics of a webcam paired with optics designed for short distance focus.
  2. Keep the camera but augment the optics with a clip-on macro lens. These are sold with the intent they let cell phone cameras focus on objects closer than they normally could.

Either should allow me to measure more accurately and tune the steps-per-millimeter value. While I contemplate my options, I went back into my UWP application to play around with a few other features.

Quick Notes on UWP Layout

Layout is another big can of worms in UWP application development, but having spent far too much time on keyboard navigation I’m postponing the big lessons until later. Today I’m going to learn just enough to get what I want on screen.

The first is controlling that shape I drew earlier. By default simple shapes (Ellipse, Rectangle, etc) dynamically adjusts to layout size, but there doesn’t seem to be a way to specify complex shapes that would be similarly dynamic. They are specified via X,Y coordinates and I didn’t find a way to specify “X is 25% of ActualWidth” in markup.

The fallback is to listen to SizeChanged event and recalculate coordinates based on ActualHeight and ActualWidth. I get my little camera preview overlay graphics on screen, but that’s only the start. I wanted to draw other on screen directional controls to augment the arrow keys.

While working to position the shape and on screen controls, I ran into a frustrating problem: there are two different ways to specify an on screen color for rendering. We have Windows.UI.Color and then we have an entirely different System.Drawing.Color. I’m sure there’s a good explanation on the history here, but right now it’s just annoying to have the “Color” class be ambiguous.

Rendering the user controls outside of camera got a tiny bit tricker, because now I have to track what happens when, including when an element is loaded for me to kick off other events relating to serial communication. Thanks to this Stack Overflow thread, I learned there are three different candidates depending on need. There’s Loaded, or LayoutUpdated, or SizeChanged. And people are constantly surprised when one of them does something unexpected, it seems like none of the three does exactly what people would want. This is just one of many parts making UWP layout confusing.

When I added controls by hand, they were fully adjacent to each other with no space in between them. I knew I needed to specify either a margin, or a padding, but couldn’t figure out which is which. I still don’t… they do slightly different things under different circumstances. To ensure elements inside a grid don’t butt up against each other, I have to use Padding. To ensure the video preview doesn’t butt up against edge of the window frame, I have to use Margin. I have yet to build an intuition on which is the right tool for the job, which I hope will come with practice.

But never mind little layout details… I have my G-code controlled camera, and I want to know if it works like I wanted. (Spoiler: it didn’t.)

Quick Notes on UWP Drawing

Because I wanted to handle keyboard events, I created an UserControl that packages the CaptureElement displaying the camera preview. Doing this allowed an easy solution to another problem I foresaw but didn’t immediately know how to solve: How do I draw reference marks over the camera preview? I’d definitely need something to mark the center, and maybe additional marks for horizontal/vertical alignment and if I’m ambitious, an on screen ruler to measure distance.

With an UserControl, drawing these things became trivial: I can include graphical drawing elements as a peer of CaptureElement in my UserControl template, and we are off to the races.

Or so I thought. It is more accurate to say I was off to an entirely different set of problems. The first was making marks legible regardless of camera image. That means I can’t just use a bright color, because that would blend in on a bright background. Likewise, a dark color would be lost in a dark background. What I need is a combination of high contrast colors to ensure they are visible independent of background characteristics. I had thought: easy! Draw two shapes with different stroke thickness. I first draw a rectangle with a thicker stroke, like this blue rectangle:


I then drew a yellow rectangle with half the stroke thickness, expecting it to sit in the center of the blue stroke. But it didn’t! The yellow covered the outer half leaving the inner half, instead of my expectation of a yellow line with blue on either side. But even though this was unexpected, it was still acceptable because that gave me the contrasting colors I wanted.


This only barely scratches the surface of UWP drawing capability, but I have what I need for today. I’ve spent far too much time on UWP keyboard navigation and I’m eager to move forward to make more progress. Drawing a single screen element is fun, but to be useful they need to coexist with other elements, which means layout comes into the picture.

User Interface Taking Control

Once I finally figured out that keyboard events require objects derived from UWP’s Control class, the rest was pretty easy. UWP has a large library of common controls to draw from, but none really fit what I’m trying to present to the user.

What came closest is a ScrollViewer, designed to present information that does not fit on screen and allows the user to scroll around the full extents much as my camera on a 3D printer carriage can move around the XY extents of the 3D printer. However, the rendering mechanism is different. ScrollViewer is designed to let me drop a large piece of content (example: a very large or high resolution image) into the application and let ScrollViewer handle the rest independently. But that’s not what I have here – in order for scrolling to be mirrored to physical motion of 3D printer carriage, I need to be involved in the process.

Lacking a suitable fit in the list of stock controls, I proceeded to build a simple custom control (based on the UserControl class) that is a composite of other existing elements, starting with the CaptureElement displaying the webcam preview. And unlike on CaptureElement, the OnKeyDown and OnKeyUp event handlers do get called when defined on a UserControl. We are in business!

Once called, I have the option to handle it, in this case translating directional desire into G-code to be sent to the 3D printer. My code behavior fits under the umbrella of “inner navigation”, where a control can take over keyboard navigation semantics inside its scope.

I also have the ability to define special keys inside my scope, called accelerators ([Control] + [some key]) or access ([Alt] + [some key]) keys. I won’t worry about it for this first pass, but they can be very powerful when well designed and a huge productivity booster for power users. They also have a big role in making an application keyboard accessible. Again while it is a very important topic for retail software, it’s one of the details I can afford to push aside for a quick prototype. But it’ll be interesting to dive in sometime in the future, it’s a whole topic in and of itself. There’s literally a book on it!

In the meantime, I have a custom UserControl and I want to draw some of my own graphics on screen.

My Problem Was One Of Control

For my computer-controlled camera project, I thought it would be good to let the user control position via arrow keys on the keyboard. My quick-and-dirty first attempt failed, so I dived into UWP documentation. After spending a lot of time reading about nuts and bolts of keyboard navigation, I finally found my problem and it’s one of the cases when the answer has been in my face the whole time.

When my key press event handlers failed to trigger, the first page I went to is the Keyboard Events page. This page has a lot of information up front and center about eligibility requirements to receive keyboard events, here’s an excerpt from the page:

For a control to receive input focus, it must be enabled, visible, and have IsTabStop and HitTestVisible property values of true. This is the default state for most controls.

My blindness was reading the word “control” in the general sense of a visual element on the page for user interaction. Which is why I kept overlooking the lesson it was trying to tell me: if I want keyboard events, I have to use something that is derived from the UWP Control object. In other words, not “control” in the generic language case but “Control” as a specific proper name in the object hierarchy. I would have been better informed about the distinction if they had capitalized Control, or linked to the page for the formal Control object, or any of a number other things to differentiate it as a specific term and not a generic word. But for whatever reason they chose not to, and I failed to comprehend the significance of the word again and again. It wasn’t until I was on the Keyboard Accessibility page did I see this requirement clearly and very specifically spelled out:

Only classes that derive from Control support focus and tab navigation.

The CaptureElement control (generic name) used in the UWP webcam example is not derived from Control (proper name) and that’s why I have not been receiving the keyboard events. Once I finally understood my mistake, it was easy to fix.

Tab and Arrow Keys Getting In Each Others Way

In a UWP application, we have two major ways for navigating UI controls using the keyboard: a linear path using Tab key (and shift-Tab to go backwards), and a two-dimensional system with the four arrow keys. A part of what makes learning UWP keyboard navigation difficult is the fact that these two methods are both active simultaneously and we have to think about what happens when an user switches between them.

Application authors can control tabbing order by setting TabIndex. It is also the starting point of keyboard navigation, since the initial focus is on the element with the highest TabIndex. Occasionally the author would want to exclude something from tabbing order, they could turn that off by setting IsTabStop to false. I thought that was pretty easy until I started reading about TabFocusNavigation. This is where I’m thankful for the animation illustrating the concept on this page or else I would have been completely lost.

On the arrow navigation side, XYFocusKeyboardNavigation is how authors can disable arrow navigation. But since it is far from a simple system, selectively disabling certain parts of the app would have wildly different effects than simple “on” or “off” due to how subtrees of controls interact. That got pretty confusing, and that’s even before we start trying to understand how to explicitly control the behavior of each arrow direction with the XY focus navigation strategies.

Even with all these complex options, I was skeptical they could cover all possible scenarios. And judging by the fact we have an entire page devoted to programmatic focus navigation, I guess they didn’t manage. When the UI designer wants something that just can’t be declared using existing mechanisms, the application developer has the option of writing code to wrangle keyboard focus.

But right now my problem isn’t keyboard navigation behaving differently from what I wanted… the problem is that I don’t see keyboard events at all. My answer was elsewhere: I had no control, in both senses of the word.

Scott Locklin’s Take on Robotics

As someone who writes about robots on WordPress, I am frequently shown what other people have written about robots on WordPress. Like this post titled “Open problems in Robotics” by Scott Licklin and I agree with his conclusion: state of the art robotics still struggle to perform tasks that an average one year old human child can do with ease.

He is honest with a disclaimer that he is not a Serious Robotics Researcher, merely a technically competent spectator taking a quick survey of the current state of the art. That’s pretty much the same position I am in, and I agree with his list of big problems that are known and generally unsolved. But more importantly, he was able to explain these unsolved problems in generally understandable terms and not fall into field jargon as longtime practitioners (or wanna-be posers like myself) would be tempted to do. If someone not well versed in the field is curious to see how a new perspective might be able to contribute, Scott’s list is not a bad place to start. Robotics research still has a ton of room for newcomers to bring new ideas and new solutions.

Another important aspect of Scott’s writing is making it clear that unsolved does not mean unsolvable, a tone I see all too frequently from naysayers claiming robotics research is doomed to failure and a waste of time and money. Robotics research has certainly been time consuming and expensive, but I think it’s a stretch to say it’ll stay that way forever.

However, Scott is pessimistic that algorithms running on computers as we know them today would ever solve these problems, hypothesizing that robots would not be successful until they take a different approach to cognition. “more like a simulacrum of a simple nervous system than writing python code in ROS” and here our opinions differ. I agree current computing systems built on silicon aren’t able to duplicate brains built on proteins, but I don’t agree that is a requirement for success.

We have many examples in our daily lives where a human invention works nothing like their natural world inspiration, but have been proven useful regardless of that dissimilarity. Hydraulic cylinders are nothing like muscles, bearings and shafts are nothing like joints, and a Boeing 747 flies nothing like an eagle. I believe robots can effectively operate in our world without having brains that think the way human brains do.

But hey, what do I know? I’m not a big shot researcher, either. So the most honest thing to do is to end my WordPress post here with the exact same words Scott did:

But really, all I know about robotics is that it’s pretty difficult.

Randomized Dungeon Crawling Levels for Robots

I’ve spent more time than I should have on Diablo III, a video game where our hero adventures through endless series of challenges. Each level in the game has a randomly generated layout so it’s not possible to memorize where the most rewarding monsters live or where the best treasures are hidden. This keeps the game interesting because every level is an exploration in an environment I’ve never seen before and will never see its exact duplicate again.

This is what came to my mind when I learned of WorldForge, a new feature of AWS RoboMaker. For those who don’t know: RoboMaker is an AWS offering built around ROS (Robot Operating System) that lets robot builders leverage the advantages of AWS. One example most closely relevant to WorldForge is the ability to run multiple virtual robot simulations in parallel across a large number of AWS machines. It’ll cost money, of course, but less than buying a large number of actual physical computers to run those simulations.

But running a lot of simulations isn’t very useful whey they are all running the same robot through the same test environment, and this is where WorldForge comes in. It’s a tool that accepts a set of parameters, then generate a set of simulation worlds that randomly place or replace features according to those given parameters. Then virtual robots can be set loose to do their thing across AWS machines running in parallel. Consistent successful completion across different environments builds confidence our robot logic is properly generalized and not just memorizing where the best treasures are buried. So basically, a randomized dungeon crawler adventure for virtual robots.

WorldForge launched with ability to generate randomized residential environments, useful for testing robots intended for home use. To broaden the appeal of WorldForge, other types of environments are coming in the future. So robots won’t get bored with the residential tileset, they’ll also get industrial and business tilesets and more to come.

I hope they appreciate the effort to keep their games interesting.

Learning UWP Keyboard Navigation

After a quick review of the of UWP keyboard event basics, I opened up the can of worms that is keyboard navigation. I stumbled into this because I wanted to use arrow keys to move the 3D printer carriage holding a camera, but arrow keys already have roles in an application framework! My first effort to respond to arrow keys was a failure, and I hypothesized that my code conflicted with existing mechanisms for arrow keys. In order to figure out how I can write arrow key handlers that coexist with existing mechanisms, I must first learn what they are.

Graphical user interfaces are optimized for pointing devices like a mouse, stylus, or touchscreen. But that’s not always available, and so the user needs to be able to move around on screen with the keyboard. Hence the thick book of rules that is summarized by the UWP focus navigation page. As far as I can tell, it is an effort to put together all the ways arrow keys were used to move things around on screen. A lot of these things are conventions that we’ve become familiar with without really thinking about it as a rigorous system of rules, many were developed by application authors so it “felt right” for their specific application. It reminds me of the English language: native speakers have an intuitive sense of the rules, but trying to write down those rules is hard. More often than not, the resulting rules make no sense when we just read the words.

And, sadly, I think the exact same thing happened in the world of keyboard navigation. But in a tiny bit of good news, we’re not dependent on understanding words, this page also had a lot of animated graphics to illustrate how keyboard navigation functions under different scenarios. I can’t say it makes intuitive sense, but at least seeing the graphics help understand the intent being described. It’s especially helpful in scenarios where tab navigation interacts with arrow key navigation.

Reviewing UWP Keyboard Routed Events

I wanted to have keyboard control of the 3D printer carriage, moving the webcam view by pressing arrow keys. I knew enough about the application framework to know I needed to implement handlers for the KeyDown and KeyUp events, but in my first implementation those handlers are never called.

If at first I don’t succeed, it’s time to go to the manual.

The first stop is the overview for UWP Events and Routed Events, the umbrella of event processing architecture including keyboard events. It was an useful review and I was glad I hadn’t forgotten anything fundamental or have missed anything significantly new.

Next stop was the UI design document for keyboard interactions. Again this was technically a review, but I’ve forgotten much of this information. Keyboard handling is complicated! It’s not just an array of buttons, there are a lot of interactions between keys and conventions build up over decades as to what computer literate users have come to expect.

When I think of key interactions, my first reaction is to think about the shift key and control key. These modifier keys change the meaning of another button: the difference between lowercase ‘c’, uppercase ‘C’ and Control+C which might be anything from “interrupt command line program” to “Copy to clipboard.”

But that’s not important to my current project. My desire to move the camera carriage using arrow keys opened up an entirely different can of worms: keyboard navigation.

Webcam Test with UWP

Once I had an old webcam taped to the carriage of a retired 3D printer, I shifted focus to writing code to coordinate the electronic and mechanical bits. My most recent experiments in application development were in the Microsoft UWP platform, so I’m going to continue that momentum until I find a good reason to switch to something else.

Microsoft’s development documentation site quickly pointed me to an example that implements a simple camera preview control. It looks like the intent here is to put up a low resolution preview so the user can frame the camera prior to taking a high resolution still image. This should suffice as a starting point.

In order to gain access to the camera feed, my application must declare the webcam capability. This will show the user a dialog box that the application wants to access the camera with options to approve or deny, and the user must approve before I could get video. Confusingly, that was not enough. If I approve camera access I still see errors. It turns out that even though I didn’t care about audio, I had to request access for the microphone as well. This seems like a bug but a simple enough workaround in the short term.

Once that was in place, I got a low resolution video feed from the camera. I don’t see any way to adjust parameters of this live video. I would like to shift to a higher resolution and I’m willing to accept lower frame rate. I would also like to reduce noise and I’m willing to accept lower brightness. The closest thing I found to camera options is something called “camera profiles“. For the moment this is a moot point because when I queried for profiles on this camera, IsVideoProfileSupported returned false.

I imagine there is another code path to obtain video feed, used by video conference applications and video recording apps. There must be a way to select different resolutions and adjust other parameters, but I have a basic feed now so I’m content to put that on the TO-DO list and move on.

The next desire is ability to select a different camera, since laptops usually have a built-in camera and I would attach another via USB. Thanks to this thread on Stack Overflow, I found a way to do so by setting VideoDeviceId property of MediaCaptureInitializationSettings.

And yay, I have a video feed! Now I want to move the 3D printer carriage by pressing the arrow keys. I created keyboard event handlers KeyDown and KeyUp for my application, but the handlers were never called. My effort to understand this problem became the entry point for a deep rabbit hole into the world of keyboard events in UWP.

[Code for this exploration is public on Github.]

And I Ended Up Using Tape

Now I feel ridiculous. After spending time disassembling a HP HD 4310 webcam to see how to best modify it for mounting on the carriage of my retired 3D printer chassis… I realized the fastest and easiest way to test some ideas is to just tape the thing to the carriage with good old reliable blue painter’s tape.

The tape would not be sturdy enough for precision measurements, of course, but that’s not important on the first pass through. I needed to see if the camera can autofocus within the range I want, and I need to see the quality of images I can get with this camera. And most of all, I need to verify I could write the code necessary to control everything working together as a unit. None of that need a rigid mounting.

Right now the biggest problem is the USB cable exerting a force as the carriage moves around. It is a pretty soft cable, but strong enough to wiggle a taped-down camera. I suspect any kind of 3D printed bracket would be enough to resist the force exerted by the USB cable.

In the short term, this is not a huge problem. Tape on the left and right sides of the camera has good leverage to resist the cable as the carriage moves along the X axis, and Y-axis movements would not exert any force at all since it is an independent assembly.

So a little blue tape is all I need right now to let me get started on the coding.

Mild HP HD 4310 Webcam Integration Modification

I took a HP HD 4310 webcam apart to see inside. Mainly out of curiosity and for fun, but also to check out my options for system integration. Webcams generally come with some kind of mechanism that helps them perch on top of a wide variety of surfaces, ranging from flat tabletop to the narrow bevel of a computer monitor. One thing they are not designed for, however, is to be rigidly mounted to a 3D printer chassis. Some webcam bases have integrated a standard 1/4″-20 camera tripod mount, but the HP HD 4310 is not one of them.

The built in base on a HD 4310 can unfold to sit flat on a surface, or grasp a computer monitor. In my intended usage, however, it is not useful and gets in the way. Fortunately, once we take the case apart we could access the single screw necessary to remove the base.

I considered designing and 3D printing something to slot in the exact same position as the base, but it is small and the single attachment point is difficult to ensure rigidity. (A problem in its normal usage as a webcam as well.) I think it is more likely for me to remove the two short case screws and replace them with longer screws. This allows attachment to a much wider and therefore more stable bracket.

I was also concerned about inadvertent button presses launching functions unexpectedly. I don’t plan to use the buttons so I had planned to cut some traces on the circuit board to disable those buttons. Fortunately, the physical buttons can be removed to eliminate inadvertent activation.

These mild modifications should be enough to help me get started. If I want to go further, there’s the option to host the circuit board in a new enclosure. The main obstacle here is the USB data cable: its hard rubber protective strain relief bushing on the back shell has been installed very tightly. I suspect it could not be removed without destroying the back shell, the cable, or possibly both. The other option is to cut the wires and build my own USB data cable, but I’m not willing to put in that much effort for an early first draft prototype. In fact, I probably shouldn’t have put in the amount of effort I already have.

HP Webcam HD 4310 Teardown

Since there’s currently a shortage of high quality webcams, an old and long discontinued HD 4310 has been repurposed for the current exploration. The fact it is not brand new also makes it less psychologically intimidating to tailor the device to suit. Since there’s no warranty left to worry about voiding, I’m going to open it up to see what I have to work with.

The two black circular depressions in the back were stickers, easily taken off to access screws underneath. Once the screws were gone, the plastic enclosure proved to be two pieces of plastic held by clips and could be pried apart with mild effort.

When the two halves popped apart, the buttons flew out as well. Though the three buttons are individually rigid, they are held together by a flexible strip. On the back shell, we could see a single screw holding the webcam stand in place. The stand slid out easily when that lone screw was removed.

Everything else seems to be mounted to a single circuit board, which was expected. Except for the single microphone, which was a mild surprise. The front exterior shape had two perforated grills that implied a pair of microphones. Also, I had expected those two microphones to be surface mounted to the circuit board, so it was a surprise to see only a single microphone that was not surface mount. It wasn’t even aligned with the perforated grill! I thought that would compromise sound quality, but I’m no audio engineer.

The circuit board was held by two more screws. Before I took them off, I considered the possibility that the front shell was part of the optical assembly. There’s a risk that when I pick up the camera I’ll scatter little lens mechanisms all over my work table. If this was a brand new unit I might have backed off, but it wasn’t, so I proceeded.

Fortunately the camera and lens assembly was an integrated unit and nothing flew out as the buttons did earlier. Once removed we could see the audio guide sending sound from one small part of the perforated front grill to the microphone. We could also see the three buttons up top, and the connector for USB.

Armed with knowledge of what’s inside its plastic enclosure, I can come up with a plan on how to integrate this peripheral into a project.

The Great Webcam Shortage of 2020

Sometimes a project idea comes up and is hampered by the most unexpected of problems. The visual dimension measuring machine project (I need to come up with a better name) is mechanically speaking a camera bolted to the carriage of a former 3D printer. I wanted to explore how precisely controlled camera movements can help capture precise dimensions of an object in view.

I’ve been working on the former 3D printer, bringing a retired Geeetech A10 back up and running. I then started looking into the webcam side. I wanted something better than the average camera built into the screen bezel of a laptop. Ideally this meant a good optical lens assembly with auto focus capability, and not the more common fixed-focus cameras with mediocre lenses barely better than a pinhole camera.

And… all the good webcams are sold out! I had not known we were in the middle of the Great Webcam Shortage of 2020, but it made sense. A lot of officers workers have switched to working at home, and I’m not the only one dissatisfied with the camera built in to our laptops. Thus the demand for an upgraded camera shot up well past historical norms, and manufacturers are scrambling to meet demand.

So the first draft of my project will have to make do with a webcam I already had on hand, which is probably a good idea for a prototype anyway. I have a HP Webcam HD 4310 I can draft for the purpose. I had been using it to monitor my 3D prints via OctoPi, but that printer is currently offline anyway so the camera is available.

The print on the outside proclaims “1080P HD” and “Auto Focus”. I’m not sure the former is true – it does have the option to output 1080P but the visual quality is rather less than I expected at that resolution. I strongly suspect that 1080P is not the native sensor resolution, but an upscaled image. The alternate explanation is that the 1080P sensor is hampered by poor lens. Either way, it’ll have to do, and at least it does offer auto focus! Let’s find out what’s inside.

Project Precedent: Optical Comparator

I’m vaguely aware of the existence of computer-controlled camera inspection systems in industrial quality assurance, but that’s not the inspiration for my next experiment to mount a camera on a 3D printer chassis. The inspiration was actually an optical comparator I used when I took a class in machining technology.

Using it started with mounting a machined part in the examination area, then the shadow of its profile is magnified and projected up on a large screen for inspection of geometry. Older machines only performed the optical magnification, the actual comparison was done by a human being with a transparent overlay of the intended dimensions placed on the screen for comparison. (Hence the name optical comparator.) The one I got some hands-on time for was one of the newer machines with digital read out, plus a computer capable of performing some basic geometry calculations. For example, I could put the cross hairs on three different points of a hole, and the calculator will return the center point and diameter of that hole.

That center cross hair was what I’m focused on for my project. A real optical comparator is designed to maximize the area sharply in focus while simultaneously minimizing distortion in the projected image. This requires an elaborate optical path filled with expensive lenses, and I have neither the skill or budget to replicate that capability. Most of what I want to accomplish can be tied to that center cross hair in conjunction with precision motion control, ignoring the effects of distortion like parallax out towards the edges.

It is possible to do much of what I intend to with OpenCV and a static high quality calibrated camera, skipping the motion control bits. However the point of this project is to use motion control to compensate for the various problems encountered when using an affordable webcam. This is how the project is inspired by, but very different from, just building a cheap crude optical comparator.

So now with the 3D printer chassis in hand, all I need is a webcam! OK, well, about that

Idea: Visual Dimension Measurement

I had the chance to inherit a retired Geeetech A10 3D printer, minus many of the 3D printing specific parts. I gave it some power and devised a replacement for the missing Z-axis end stop. While this was not enough to restore it to 3D printing ability, it is now a functioning 3-axis motion control system. What can I do with it?

The problem is not trying to come up with ideas… the problem is trying to decide which idea to try first. Motion control systems used to be strictly in the realm of industrial machinery, but 3D printing has brought such capability within reach of hobbyists and now we are here: systems getting old and available for re-purposing.

I’ve decided the first idea I wanted to investigate was a camera based measurement system. Using a camera mounted to the carriage, measure and calculate dimensions of things placed on the bed. I’ve wanted this kind of capability many times in past projects, designing enclosures or brackets or something else for 3D printing to support an existing item.

Most typically, I’ve wanted to quickly measure the dimensions of a circuit board. Sometimes that’s because I have a salvaged piece of equipment and I wanted to repurpose it into something else. Other times it’s because I bought some electronic component on Amazon and I wanted to build an enclosure for it. It’s easy to use a caliper when they are rectangular, but they’re not always so cooperative.

People have asked if they could get dimensions from a photo. This is possible if the camera has been calibrated and its optical characteristics known. Lacking that information, a photograph is a 2D projection of 3D data and this transformation loses data along the way that we can’t reliably extract afterwards.

But there’s another way: if the camera’s movement is precisely controlled, we can make our calculations based on camera’s motion without a lot of math on optical projection. Is it easier or harder? Is it more or less accurate? It’s time to build a prototype of something that can be thought of as a crude optical comparator.

Seeed Studio Odyssey X86J4105 Has Good ROS2 Potential

If I were to experiment with upgrading my Sawppy to ROS2 right now, with what I have on hand, I would start by putting Ubuntu ARM64 on a Raspberry Pi 3 for a quick “Hello World”. However, I would also expect to quickly run into limitations of a Pi 3. If I wanted to buy myself a little more headroom, what would I do?

The Pi 4 is an obvious step up from the 3, but if I’m going to spend money, the Seeed Studio Odyssey X86J4105 is a very promising candidate. Unlike the Pi, it has an Intel Celeron processor on board so I can build x86_64 binaries on my desktop machine and copy them straight over. Something I hope to eventually be a painless option for ROS2 cross compilation to ARM, but we’re not there yet.

This board is larger than a Raspberry Pi, but still well within Sawppy’s carrying capacity. It’s also very interesting that they copied the GPIO pin layout from Raspberry Pi, the idea some HATs can just plug right in is very enticing. Although that’s not a capability that would be immediately useful for Sawppy specifically.

The onboard Arduino co-processor is only useful for this application if it can fit within a ROS2 ecosystem, and the good news is that it is based on the SAMD21. Which makes it powerful enough to run micro-ROS, an option not available to the old school ATmega32U4 on the LattePanda boards.

And finally, the electrical power supply requirements are very robot friendly. The spec sheet lists DC input voltage requirement at 12V-19V, implying we can just put 4S LiPo power straight into the barrel jack and onboard voltage regulators will do the rest.

The combination of computing power, I/O, and power flexibility makes this board even more interesting than an Up Board. Definitely something to keep in mind for Sawppy contemplation and maybe I’ll click “Add to Cart” on this nifty little board (*) sometime in the near future.

(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.