The Motivation

It’s nice to have a souvenir when I come back from vacation: a shot glass, a knick-knack, a T-shirt; a little reminder helps the trip last longer in my mind.

On my last vacation, I realized how much buying souvenirs grates on my diy sensibilites. I wanted a T-Shirt, but I didn’t want what they were selling. I wanted something simple. I wanted the design I had unconsciously completed in my head.

Something clicked. I decided that instead spending $20 on a $5 cookie-cutter T-shirt, I would make my own shirt as soon as I got home.

Attempt #1

Unfortunately, I was travelling for business the next week. Still, I would not be denied! I had found an Instructable that seemed doable. I ran out to a craft store and pick up my supplies.

Because I was traveling, however, I cut a few corners. I didn’t want to spend $8 on modge-podge, just to have to throw it out (>3oz.) So instead, I used watered down glue on a cut-up stocking. What could go wrong?!

Answer? Everything. While I thought the stocking’s stretchiness would be an asset, Tt allowed the entire pattern to move around. The watered-down glue also failed. Capillary action made it want to fill each opening, leading to a pixellated effect.

Attempt #2

When I got home from my trip, I experimented a little more. Instead of a stocking, I used an old sheer window curtain. To keep the letters nice and crisp, I tried JB Weld as a masking agent. And, just to see if it was the water that was messing me up, I used undiluted glue to mask the perimeter.

I actually had enough confidence to ink this screen. It didn’t look too bad, but this method had some clear drawbacks:

• Laying down the JB weld was a huge pain. I needed to mask the area with tape, apply the epoxy, let it set, then remove the tape before things fully cured
• The glue still didn’t work all that well. There was still a pixel effect, and in some areas it failed to stop the ink from getting through.

Final Attempt

Mulling things over a bit, I wondered if I could just use something like tape for my mask. It worked for shaping the JB Weld, maybe it would work for ink as well.

Some searching in this vein led me to a different Instructable, by Chris Connors. (Oddly, I know Chris.) He doesn’t use tape, but adhesive vinyl for his mask.

This vinyl mask, combined with the fabric hoop from the first Instructable, wound up being a winning combination.

To Sum Up…

Oh hell yes. I just discovered that I can make my own custom T-shirts for <2$ in consumables. The total bill at the craft store was probably 15$ but that was for enough material to make / ink a dozen different designs.

And it can travel! Apart from the cutting tool, everything will fit easily into a carry-on. Maybe next time I'll make my vacation t-shirt while I'm still on vacation.

Oh, one last thing: I've detailed my entire method in my own Instructable, if you’d like to try this for yourself.

Here’s a direct link to his file. In case that goes down I’ve also set up a local mirror here.

Well it looks like the PID Library has made it on to another wild Kickstarter ride. This time it’s with the Nomiku: an ingenious sous-vide solution. I’m a sucker for forehead-smack ideas, and this product is a great one. Rather than sell you an entire bulky unit, the Nomiku a small, easy to store, device that clips to a pot you already have.

The icing on the cake is that I know these guys. I met them at makerfaire last year and they’re great; very passionate about this stuff. Actually, it seemed like they were just passionate. about everything. I’m really glad that this is working out for them!

This is what I love about working on base-level components. I only have to do the work once, and then I get to see it crop up in tons of cool stuff. It makes me proud to know I helped those people along a little. I can only imagine how the Arduino team feels.

A few years ago, I started making offset headers for the Arduino. These headers allow you to make shields using standard-spaced perfboard, by correcting the shift of that one strangely-placed Arduino header.

With the introduction of the Leonardo, The Arduino team kept the shift of the header, but added two pins to it.

Too keep up in this offset header arms race, I ordered some 10-pin headers and modified my fabrication process to accept the two extra pins. I expect these to find their way into the hands of fine retailers over the next couple of months.

Bear with me. I’ve come up with a pretty decent life hack. I think it’s good enough that I’ve decided to diverge from my regular 3D printing and PID control fare, and post a picture of a toilet.

Here’s the trick: Rather than freshening the air after doing your business, plan ahead. A half-second spray into the toilet beforehand is all you need. Its a confined space, so everything gets “pre-treated,” as it were.

You use less spray, you ensure that all your foul air is treated at the source, AND you don’t need to smell your own filth. Enjoy!

Spring is here, and that means it’s time to prepare for summer parties. If you’re me, that means making a ladder golf set. It seems like every year I’m making another one, the previous-year’s set having been gifted or left somewhere.

Over the years I’ve picked up a few tricks, and this time around I finally remembered to document them.

When making the bolas, I’ve found the through-hole method to be rock-solid and maintenance free. It took me a little while to find a painless way to crank these out.

I like to use a 1/4″ nylon rope and a 1/4″ hole, so stringing the rope can be difficult. My first trick is to taper the rope at the tip and tape it to something thin and rigid. Here I’m using a skewer, but I’ve used a piece of wire in the past.

The second trick is to put all the golf balls on the rope first, before double-knotting and cutting each bola.

The last thing I do on each bola is melt the end of the rope with an open flame, permanently locking the knot in place.

Making the ladder is straight-forward, so I won’t bother explaining that in detail. Two things I’ve learned though:

• You don’t need to use the purple pvc primer. This doesn’t have to be water tight, and the primer tends to run all over and makes things ugly
• A ratcheting tube cutter is worth every penny. It turns a long, messy job into a quick, clean one

I also tried something new this year. One of the things that bothered me about my previous ladders was the number of pieces. Each ladder breaks down into 3 pieces, which makes storage and transport a little annoying.

Using some of the left-over bola rope, I turned each ladder into a single unit with a shoulder strap. I’m pretty happy with how they came out, and with my design improvements.

One of my main issues was the size. I really wanted to make it smaller, but I didn’t want to pay for a small cartridge heater.

It occurred to me a couple of days ago that I might be able to modify a stock toaster-oven heating element to make a smaller heater. If I cut out a small section and drove it at a proportionally smaller voltage, I wondered, could I get a small heater with the same temperature as the big boy? It turns out that the answer is yes.

I went through a few fits and starts getting this thing to work. My main issue is that I’m still learning to weld, and welding wire requires a lot of finesse. I’m not going to bother with the trials and tribulations though. Here’s how I made a custom heating element:

Cut to Length

A heating element is a nichrome coil embedded in a steel tube using ceramic. In a toaster-oven they wire 2 in series, so each element is designed to see 60V. I had a 12V power supply, so I wanted to use 1/5 of the total element length. A pipe cutter made quick work of the cuts.

Ream

I needed to attach metal contacts to the wire. To give myself enough wire for a bond, and to have room to support the contact, some free space would be required. A metal file and some elbow grease left me with a 1/4″ cavity at each end of my cut section.

Weld

Attaching things to nichrome is a tricky proposition. Because it gets so hot you can’t use solder, and mechanical connections are unreliable. I decided TIG welding was the way to go.

Easy in theory, blindingly difficult (for me) in practice. In the end though, welding for 250mS at the lowest setting created a permanent bond bond between contact and wire.

Insulate

To keep this welded bond electrically isolated, and to give the contact some rigidity, I filled the previously-created cavity with furnace cement.

Next time around I might do this in several small additions rather than all at once. I think that would give me a more solid fill.

Burn Baby Burn

It actually works! I applied 12V to the element and was easily able to make some wood smoke. It didn’t get red-hot, but I suspect this is because my cut section was a bit long. At any rate, I’m really excited at the prospect of making inexpensive small heaters for use in my projects. I should probably get some more welding practice first though.

Then something awful happened:  I enjoyed it.  For me, that means that I would have to keep doing it at least until I felt proficient.

This part of my personality can be really annoying sometimes, but I’ve learned it’s impossible to fight.  The quickest way to get stuff out of my system is to challenge the hell out of myself to quickly get to that proficient feeling.

So I decided I would make a hat. A difficult hat.  One that I definitely couldn’t buy.  It would be a multi-color hat with a custom pattern, allowing me to show off my love of oshw during the winter months.

Fair-isle

My first attempt at multi-color was using the fair-isle technique, whereby the unused colors are carried behind the knitting and occasionally wrapped in place.

I was ambitious, and went for a 3-color test pattern:

It turned out pretty well for a first try, but I didn’t particularly like the process or the end result.  Keeping track of 3 colors and wrapping was not enjoyable, and the final product felt pretty stiff.

Double knitting, Attempt #1

For the actual hat, I dropped my pattern down to two colors to improve the readibility of the image. I also settled on a different, double-knitting, technique. One of the benefits of double knitting is that it produces a reversible fabric, which you don’t see all that often.

Armed with my pattern and a 16″ circular needle, I got to work.  Once I got past the pattern I switched to double-pointed needles and reduced the hat by 6 stiches/row.  I was really happy with how everything turned out:

…until I tried it on.  It was too small, both in diameter and height.  I was able to make it fit on the dog though.

Double Knitting, Attempt #2

God I was pissed.  I added some length and width to my pattern.  To make sure I didn’t screw up the size on my second try I also got a 40″ circular needle.  I still used a 16″ for the main part of the hat, but I periodically threaded in the 40″ so that I could test-fit.

On the reduction section, a 40″ magic loop proved vastly superior to the double-ended needles.  I started by reducing 3 stitches a row, testing the fit every few rows.

Once I was near the top of my head I switched to 6 sticthes a row, closing off the hat.

I am very happy with the results:

And the good news is I don’t feel like I have to knit anymore.  I’ve found it to be a great activity while flying or riding in the car, so I might still dabble.  That crazy urge to get decent, however, seems to have been satiated.

A note about the pattern

For the fair isle pattern I was all proud of using various tricks in mspaint to make it. Then I discovered this method by Becky Stern:

It’s embarassingly better than my mspaint crap. For the double-knit pattern I used her method.  One thing I did differently was to use 10×6 pixel rectangles instead of squares.  I had found during a test swatch that my stitches were Wider than they were tall.  This modified grid ensured that the knit pattern would carry correctly.

While not nearly as in-depth, that’s the goal of this post. I’ll explain what the Autotune Library is trying to accomplish, and how it goes about its business.

Attribution

For A couple years I’ve wanted to have an Autotune Library, but due to an agreement with my employer, I wasn’t able to write one. BUT! when I found the AutotunerPID Toolkit by William Spinelli I was good to go; My company had no problem with me porting and augmenting and existing open source project.

I converted the code from matlab, made some tweaks to the peak identification code, and switched it from the Standard form (Kc, Ti, Td) to the Ideal form (Kp, Ki, Kd.) Other than that, all credit goes to Mr. Spinelli.

The Theory

The best tuning parameters (Kp, Ki, Kd,) for a PID controller are going to depend on what that controller is driving. The best tunings for a toaster oven are going to be different than the best tunings for a sous-vide cooker.

Autotuners attempt to figure out the nature of what the controller is driving, then back-calculate tuning parameters from that. There are various methods of doing this, but most involve changing the PID Output in some way then observing how the Input responds.

The method used in the library is known as the relay method. here’s how it works:

Starting at steady state (both Input and Output are steady,) the Output is stepped in one direction by some distance D. When the Input crosses a trigger line, the output changes to the other direction by distance D.

By analyzing how far apart the peaks are, and how big they are in relation to the output changes, the Autotuner can tell the difference between one type of process and another. As a result, different systems will get custom tuning parameters:

The Implementation

This works well in theory, but real-world data isn’t very cooperative. The input signal is usually noisy, which causes two main problems.

Problem #1: When to step?

Since a noisy signal is choppy, it’s likely that the trigger line will be crossed several times as the Input moves past it. This can cause mild chatter in the output, or if severe, can completely destroy things:

The way I chose to side-step this issue was to have the user specify a noise band. In effect, this creates two trigger lines. Since the distance between them is equal to the noise (if properly set) it’s less likely that multiple crossings will occur due to signal chatter.

Problem #2: Peak Identification

In a simulated world, identifying the peaks is easy: when the Input signal changes direction, that’s a minimum or a maximum (depending an which change occured.) In a noisy world however, this method fails:

Every noise blip is a direction change. To deal with this issue I added a “look-back time” parameter. It’s an awful name. If you can think of something better let me know.

At any rate, the user defines some window, say 10 seconds. The Library then compares the current point to the last ten seconds of data. If it is a min or a max, it gets flagged as a possible peak.

When the flagged point switches from being a max to a min, or vice versa, the previously flagged point is confirmed as a peak.

Another way of explaining the look-back time is that a point will be identified as a peak if it is the largest (or smallest) value within one look-back into the future or past. Like I said: awful name.

You should also know…

• The number of cycles performed will vary between 3 and 10. The algorithm waits until the last 3 maxima have been within 5% of each other. This is trying to ensure that we’ve reached a stable oscillation and there’s no external strangeness happening. This leads me to…
• I’m not the biggest fan of Autotune. I’ve often said, and still believe, that a moderately trained person will beat an Autotuner every day of the week. There’s just so much that can go wrong without the algorithm knowing about it. That being said, Autotune is a valuable tool to help the novice get into the ballpark.