Power Supply Hurdles

2018-09-01 16:29 - Making

My last post was about a successful step in a long delayed project. I've continued making progress, but mostly progress towards hurdles I haven't quite passed yet. I did cut out my case designs in acrylic plastic:

Laser cutting the bottom case part. The bottom case part, protective layers removed. The top case part, protective layers removed.

My case design involves a bottom part, which is also the back (after a bend). Plus the front part, which is also the sides and top after a few more bends. I didn't quite think about making all these bends, when doing the design. I folded the sides in first, and that went pretty well. Except at the left side, near those big openings in the middle. Acrylic is brittle, and I put some hairline cracks in the very narrow part across the middle and the slightly wider part near the bottom. Mostly cosmetic, so that's okay. Except that left folding the top down, which went even worse.

The case front, shattered after a bad attempt to bend the top down.

In addition to adding weak points, all these holes leave fewer places to hold on. I ended up shattering this larger front piece of the case completely, while making that last bend. Quite the bummer, but at least it leaves me the opportunity to double check a few measurements. I've got one spare piece of plastic to use for a second try. And I know to be careful when I attempt the (simpler) back piece as well.

With that physical part of the project on hold, I returned to the electrical part. There's power in, which goes through a (huge) transformer, salvaged from a bad UPS. This drops line voltage to around fifty volts, which is rectified by a circuit also cobbled together with parts from that bad UPS and some old bad computer power supplies. This goes into a pair of RDTech DPS modules, which handle voltage and current limiting for the adjustable outputs. The transformer has another tap, which produces around 18 volts. I'm going to separately use that to power a fan and a USB supply module (which was visible in the corner of the fresh-cut before-bending case front picture).

An end-to-end test set up of my power supply. Ripple voltage at the rectifier output. Power being drawn during this test.

Here's all the key parts of that set up on the bench as a test. The good news is that it works. The bad news is it doesn't work very well.

The full bridge rectifier has just a pair of 66µF capacitors smoothing it out. At first that seemed okay enough. Since I did some very early tests I've gotten an electronic load, at bottom right of the first picture above, which I can use to do more thorough testing. In that picture, it's drawing twelve volts at two amps, well below the 50V / 5A theoretical upper limits (of the DPS modules). But even at this low power level, it's causing around nine volts of ripple at the rectifier output. Far too much! I know that adding an inductor can create a much more stable rectified output. It drops the maximum voltage level, but this much ripple will too, so I'm going to experiment with inductors I can salvage, for the more reliable of the two lower voltage options. (I don't really need that whole 50 volt output range, anyway.)

Plastic Bending

2018-08-21 21:03 - Making

My first (failed) plastic bending system.

I've had a power supply project in the works for a good while. When I saw a post about bending acrylic plastic to make custom cases for electronics, I knew I'd use that technique. I didn't want to build such a big contraption though, and I delayed quite a bit. I had the system pictured above assembled some time ago, but never operated it.

More recently, I tried harder. I doubled up the length of wire, to half the resistance and thus double the power (at the same voltage). I ended up hooking a laptop power brick to the unit that will be the heart of the supply I'm building, and I finally got the bending system working! Note the spring at the far end. Over the twelve inches or so that I'm heating (in the working set-up), there's a noticeable expansion of the hot wire. The spring helps take up that slack, and keep the wire strung in a nice straight line, near the plastic to be heated.

My refined, working, acrylic bending system.

I added some L aluminum brackets to (maybe) better contain and focus the heat, and (definitely) help me hold the plastic in place correctly. I'm only energizing a short piece of the wire I've got in place. I didn't know at all what sort of voltage or current would be necessary when I started. I correctly figured that I could always connect less of it, if I put too much.

In this shot you can see the successful fruits of my tests. If I hold the plastic still above the orange hot wire, after a little while it heats to the point of becoming quite malleable. Quickly and carefully bend at that point, and the plastic will quickly cool back to being solid. I got three ninety degree bends in the test piece. I'll do a few more tests to figure out how the inside/outside ends up: what's the radius of the bend? If I try to make a box, where do I need to put the bends to know what the outside dimension will be (so it lines up with the other half of the box!)?

Either way, it feels good to have this long delayed part of the project behind me!

Moviepass is dead? (And I killed it?)

2018-08-06 23:20 - General

I found out about MoviePass mid/late last year. I probably saw an average of one movie per year until then. In general I'm patient, so I'm in no rush to see a movie in the theater, and the ticket price is more than I'm willing to pay for little benefit (from my perspective). But MoviePass allowed me to see effectively all the movies I could ever want, in the theater, for ten bucks a month. So I used it. A lot.


DateMovieTicket Cost
Sat, May 5Avengers: Infinity War$12.00*
Sun, May 6You Were Never Really Here$15.00
Sun, May 13Tully$12.00*
Sun, May 20Deadpool 2$12.00*
Sat, May 26Solo$12.00*
Sun, May 27Book Club$15.69
Thu, June 6Upgrade$17.99
Sat, June 9Ocean's 8$16.99
Sun, June 10Won't You Be My Neighbor$15.00
Fri, June 15Hotel Artemis$15.99
Sat, June 16American Animals$17.40
Sun, June 17Nancy$12.00
Sat, June 23Tag$15.99
Sun, June 24Incredibles 2$7.99**
Sat, June 30Jurassic World$16.99
Sun, July 1Hereditary$12.00*
Wed, July 4Hover$12.00
Fri, July 6Sicario: Day of the Soldado$12.00*
Tue, July 10Sorry to Bother You$15.00
Fri, July 13Three Identical Strangers$12.00*
Sat, July 14Leave No Trace$16.99
Sun, July 15Ant-Man and the Wasp$12.00*
Thu, July 19Skyscraper$17.99
Sun, July 22Hotel Transylvania 3$8.49**
Sat, July 28The Equalizer 2$12.00*

* These were E-Tickets, which MoviePass seems to get a discount on.

** These were matinees. Why did MoviePass never encourage users to go to the much cheaper matinees?

These are the ticket stubs I have lying around. I might have missed one here or there. But the long and short of it is that for these three months, while I paid MoviePass $29.85 ($9.95 × 3) they paid several local movie theaters $379.16. This is so obviously a losing proposition for them.

Death of MoviePass?

Early last month, MoviePass introduced surge pricing. With little predictability, some movies would not be included but instead come with an extra charge around $4. When this happened, I felt like I might be canceling soon. You can see an extra strong focus on the (one) local theater with E-ticketing in my watching habits over July — they are immune to surge pricing.

Then in late July MoviePass ran out of money and had a service interruption. Somewhere in there, they started forcing users to tacke pictures of their ticket stubs. (To enforce the one-viewing-per-movie rule that they added in April.) Now they've introduced more, stricter limits: from "unlimited" (one per day) to three movies per month. And very unpredictable availability (black-outs). This already started a bit. Rumors seem to be perhaps that A) every showing before 5PM (why?) and B) basically every showing of every major movie (at least for the first few weeks) will simply be unavailable. Rumors also abound about availability disappearing in the time it takes to travel to the theater.


I'm not happy. Honestly, I expected MoviePass to be short lived when I first subscribed. But that was just over nine months ago. It's survived this long, but the writing is clearly on the wall now. I'll probably keep it and extract what value I can. I'm probably getting $10/mo from it.

On the other hand, this past year has re-introduced me to the theater experience. Given a theater full of them, you're guaranteed to run into strangers that have no problem talking, turning on their bright phone screens, and generally making the theater experience less than it could be. Worst is the fixed time slots. You can see a heavy focus on weekend viewings above. I find it's quite rare for a weekday showing to both not be overlapping work hours, and also not force an uncomfortably early or late dinner. So many weekday movies start at right around six o'clock. Eating early enough to finish and then get to the theater is far too early. Eating after forces a nearly 9PM meal — I don't want to be stuck in the theater with hunger distracting me from the movie!

So I feel very lukewarm now. If I walk to a theater and then can't get into the movie; if I find I can't get a seat from limited availability after black-outs; if I just get tired investing my time in finding a compatible showing time — I won't be too sad if MoviePass ends up in my past.

Game Boy Speaker Repair

2018-07-29 13:33 - Making

The Game Boy Color, open, with the new speaker installed.

I recently picked up a Game Boy Color for cheap, due to an issue with the sound. This is a common issue, the speakers wear out or break over time. Replacements are easy to come by, and cheap. Here's mine, with the new speaker in. Turns out the cheap and easy to get replacements aren't quite perfect. The original speaker (with the "Z" on the back, outside the console) comes in a plastic case, with some nubs on the outside to hold it in place. The new one fits in that space, but it's a bit smaller. A few dabs of hot glue should keep it from rattling around. And now my Game Boy Color has sound again!

Mason Jar Soap Dispenser

2018-07-27 17:11 - General

Back when I first moved into my current apartment I went on a home furnishings spree. I got a nice soap dispenser and tumbler set that matched and looked good in place. But over time, and with exposure to water, the soap dispenser wore out quite a bit. I could never quite find something I really liked again.

Until this. I found a dispenser mechanism specifically made to attach to a mason jar. It said "any" mason jar on it, so I bought sight-unseen across the internet some mason jars. Some wide mouthed mason jars. Which didn't fit the lid it came with. Thankfully I managed to trace the hole and cut it right out with a dremel, no fuss. I've always had a minor fascination with mason jars. They feel like a basic part of the at-home, DIY spirit. Now I've got a couple at home!

RFID Reader v2 Starts

2018-06-07 23:14 - Making

The first working prototype of the next version of my RFID reader project.

I've used Arduinos for some time now, for electronics projects. They're very easy to get started with, but a little bit limited. As I called out in the VFD clock project I did a few years ago, STM32 is a nice next step up. Pictured is a Maple Mini clone I still had from that project, easily available for around $5. Even better is the (as it's colloquially known) "Blue Pill board with almost the same functionality at around $2, and it's close cousin the "Black Pill". More speed and RAM and Flash, more peripherals. More exciting!

I designed a multi-headed RFID reader project, on top of an Arduino core. After some delays it's finally seen real usage, and revealed several opportunities for improvement. Mostly around the hardware, but if I'm going to redesign, I want to take the opportunity to revisit the software as well.

On my clock project, I found the SDK very detail-heavy and hard to work with. ST Microelectronics, which makes the STM32 chips, also makes a package called STM32CubeMX, a code generator that makes the SDK easier to consume. But it wants to output projects that specifically work with a small handful of professional (read: $$$) IDE packages. I recently discovered that Atollic TrueSTUDIO, which is in that list, is available for free download! I've spent a fair deal of free time, in small chunks, recently getting these all set up and working, and especially understood.

The plan is to take advantage of FreeRTOS, which the Cube tool can include with just a click, to handle scheduling and some other things to make this next version both faster and more stable. For now at least, I've got a proof of concept, working end-to-end, able to read cards and developed with a capable IDE with breakpoints and value inspection built right in.

Custom Game Case, from Unused Koozie

2018-05-29 17:12 - Making

The pair of source Koozies, with the Game Boy Micro on top. Top sewn up, bottom cut open, sides sewn. Flipped right side out. Tucked in. Flap closed.

Several months ago I got a pair of Koozies, which have sat unused since then. More recently I've pulled out my Game Boy Micro, which has no protective case, unlike most of my portable devices. I realized that the Koozie was the right sort of material, soft and padded, and almost exactly the right size. So I cut one side of the bottom off, sewed closed the top, and sewed the sides in closer, to be the right size. After flipping it right side out and confirming a good fit, I trimmed what was the bottom of the Koozie down, to be a flap which I can tuck in to cover the open side. It worked out quite nicely!

There was a fire, a couple buildings down from mine

2018-05-28 17:49 - General

There was a fire, a couple buildings down from mine, and I had quite the view of it. I actually smelled something first as I was sitting down to work on something, flipping the switch that enabled (among other things including the light I want) my soldering iron, but it was still in sleep mode of course. Not much later, I noticed this out the window:

That's the back side of this building. Seems pretty serious, enough to have broken through the roof. I'm totally fine, but things are a bit smelly.

Here's a story about it from the Post, which says over 100 fire fighters responded, two of which ended up with minor injuries.

My phone only lets me shoot 10 minutes of video at a time, so I had to (spend 20 minutes shooting, then) re-encode to stitch two clips together. But you get to see the blaze at (what seems) its worst through to being put out by New York's Bravest.

The wi-so-serial works!

2018-03-24 21:33 - Making

The first working wi-so-serial, installed.

For months, stalled by a partially broken computer, I've been working on this project. I have a server at home (and another for remote backups, at a relative's house). And I've got full disk encryption which needs a password to unlock, at boot. Which means if it ever reboots I have to physically be there to get it going again. I'd like to be able to administer my servers remotely.

I've looked into commercial IP KVM devices, but they cost hundreds of dollars. Since I'm working with Linux here, in theory all I need is a serial terminal. So I've designed a serial-to-WiFi bridge. The picture above is the first one that I've ever had working, installed. The ribbon cable hooks up to the internal serial port header, the green terminal plugs into an unused USB port header for power. Then there's snaking trails of several other pairs of wires: one each hooking to the case and to the motherboard for the power LED, the power button, and the reset button.

Most newer motherboards power their USB ports all the time, even while the computer is off, this one included. So I can remotely power up or down, restart, and then control the computer. In theory. I've just gotten far enough to test all this, and discover performance issues. I've got all the computer-side setup to manage, yet. But after working on this since August, it's great to have it finally proven to really be workable.