Topic: Making

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!

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!

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!

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.

Hokkaido Milk Bread

2018-02-20 14:31 - Making

I recentely learned about the tangzhong bread making method. I pickeda recipe and decided to try it.

The dough is formed. Dough has risen, is divided and rolled and set in (the wrong) pan. Baked!

So I made the dough first of course. Then, I didn't know where my Mom kept her bread loaf pans so I used a Bundt pan instead. And I don't know where the pastry brush is, so I didn't do the egg wash. But it still came out quite nice. Very dense, and certainly tasty. Worth trying again with a few more details "right".

Custom Garbage Bag Holder

2017-12-25 20:24 - Making

The bag holder, "in place" except lifted up a bit for demo purposes.

Just in time* for Xmas, I put together this custom garbage bag holder for my Mom. Following availability at local grocery stores she's switched to plastic bags, and been awkwardly using them on this built in garbage bin, where they're too small to fit properly. Here's a mostly plywood contraption to fit over the existing bin, but with pegs to hold the bags' handles plus some cove molding to help keep the bag open and in place. It's about the same depth but narrower than the bin beneath it to be the right size for standard plastic shopping bags. A cutout in the lower layer of plywood fits around the lip of the bin, while the top layer holds all the bits mentioned above. It's all made from found materials already around the house, which is the perfect kind of gift for my Mom. No new/extra stuff!

* I definitely had an idea to do this over the Thanksgiving visit. And earlier in this visit. And forgot, despite a coded (to not give away the surprise) note to myself. Then I thought of it again, and realized what the note meant, and built this up over (mostly) a long afternoon on Xmas Eve.


KQ Button Tester; nee Turbo Button

2017-11-16 22:19 - Making

My KQ Turbo Button device, on a messy desk.

I've never posted here about this device I made. I made it earlier this year, mostly as a joke. On the right, now mostly hidden by the fan, is a solenoid. It sits poised above a yellow arcade button, also mostly hidden by the fan. On the front of this view is the electronics and the controls are on the top, all glued to a huge 12 volt lead acid battery.

The original point was to be able to press that button with inhuman speed and accuracy. I managed to leverage that to contribute to some of my videos about Killer Queen. More recently I've been interested in figuring out how to pick good arcade hardware. The moving parts wear out and need replacing. Which ones to buy as replacements?

So I updated the device, not only can it push the button — normally the one in the real arcade, now (in the extra little bit of wood it's sitting on) a dedicated one — it can read its value. So it can be used to derive fine details about the performance of the button, when pressed. I want to do quite a bit with this. Here's one example:

ED 0
D 12272
U 12280
D 12284
U 12540
D 12832
U 12836
D 12844
EU 0
U 8364

That starts ED 0 for "event down zero". Then a bunch of lines D and U indicate the timing of "down" and "up" events observed, in microseconds since we started the "down" event. All real mechanical switches "bounce" a bit when activated (and deactivated, usually). In this case, the button first went down about 12 milliseconds after we started (it takes some time for the solenoid coil to charge up, then to physically move) and the switch contacts bounced apart and back together three times after that, taking just over half a millisecond to settle down into its final resting state. And in this case when it came back up, there were no bounces. In my limited experience so far, this looks like good performance for such switches.

This is just one bit of data but we can compare quality in the "bounciness" category pretty easily: how many bounces, and how long before the last one is done? I intend to follow this with a post containing a detailed summary of this, for several switches. I need to make a final call on exactly what I want to measure, and make sure my tool will do that if at all possible, so it will take a little time.