I knew the project wasn’t unique, but…

Imagine my surprise, after working on my robotic glockenspiel for weeks, when I opened the Signals Catalog, and page two revealed Chimes of the Seasons Music Box, $90. The product has since been discontinued, but it was fun to see it in the catalog.

I knew the project was far from unique, but hadn’t seen such a thing in stores for years – cool that returned to the zeitgeist.

Cutting and Tuning Robotic Glockenspiel chimes

Cutting Glockenspiel pipes from 1/2" EMT Conduit
Cutting Glockenspiel pipes from 1/2″ EMT Conduit

After a few weeks of experimentation, I think I can now write sensible notes on how to cut and tune the chimes for a glockenspiel (metal xylophone) out of metal conduit. This is the first step of my Robotic Glockenspiel project, which I hope to end with a network-connected, Arduino-controlled set of chimes that can play Christmas carols.


A few bits of background, which you can ignore if you like:

  • I’m talking about pipes what will each be suspended near each end and struck in the middle.
  • Physics of such pipes says that the suspension points – the Nodes – for a pipe of length L should be at L * 0.224 from each end of the pipe.
  • A chromatic tuner usually tunes to what’s called an Even-Tempered scale. In such a scale, a note that sounds one octave above another has twice the frequency of the first note. Further, that octave is divided into 12 steps, called semitones, each of which is equally spaced (in frequency ratios) from the previous one.
  • Modern even-tempered tuning is based on a standard frequency of 440Hz – cycles per second – as an “A” in the scale.
  • Mathematically, to divide a ratio of 2 into 12 equal ratios, each ratio is the 12th root of 2, or about 1.0594630. So the frequency of each semitone is 1.0594630 times the frequency of the next lower one. Similarly, each semitone’s frequency is 1 / 1.0594630 times the frequency of the next higher one.

First cut an arbitrary length of pipe that, when tuned, will be the reference for all your pipe lengths. For 1/2″ conduit, I’d suggest cutting a piece that’s something like 400mm long – you don’t have to be exact at this point.

Once the pipe is cut, calculate the suspension points – the Nodes.
N = L * 0.224, so for a 400mm pipe, the nodes are at 400mm * 0.224 from each end. That’s 89.6mm. Since the nodes don’t have to be exact, we can use 90mm instead.

Place the 400mm pipe on the two thin supports, each support at 90mm from an end of the pipe.

Measure the frequency of the pipe by turning on the tuner then striking the pipe with your mallet (or pen).

Now you’ll need to tune the pipe by repeatedly measuring the frequency and trimming off pieces of the pipe:

  • If the tuner says that the pipe is tuned sharp- that is, above the frequency of the nearest semitone – cut a few millimeters from the pipe length and measure the pipe frequency again. Repeat this process until the tuner says the pipe is flat – that is below the frequency of the nearest semitone.
  • If the tuner says that the pipe is tuned quite flat, cut 2 or 3mm from an end of the pipe and measure the pipe frequency again. Repeat this process until the tuner says that the pipe is either slightly flat or is in tune.
  • If the tuner says that the pipe is tuned only slightly flat, use the file to file off a very little bit from the pipe, then measure the frequency again. Repeat this process until the tuner says that the pipe is in tune.  If you happen to file off too much and the pipe is tuned sharp, cut off a few mm of pipe as in the step above.

Now you have one properly tuned pipe.  Next you’ll get to cut and tune all the other pipes, based on the length of this standard pipe.

Suppose that the tuner says that your tuned pipe is an F and that measuring the length with a meter stick, you find the pipe is 396mm long.

A little more math comes in here.  Given a pipe of length L1 that rings at frequency F1, you can calculate the length, L2 of a second pipe that will ring at a desired frequency, F2.  Put mathematically, with “sqrt” standing for square root, L2 = L1 / sqrt(F2 / F1).

A little music theory comes in here as well. One way of noting the order of semitones in an octave is with sharps: C, C#, D, D#, E, F, F#, G, G#, A, A#, B, C. Also, each octave (for example, a C to the C above it) is 2 times the frequency of the lower note. You can use this list and (and the fact that an octave is 12 semitones) to count the number of semitones between your first pipe’s frequency and the frequency you want.

Suppose that you want to find the length of a pipe that is the A above your F.  From our list above, we find that A is 4 semitones above F.  So our desired frequency, F2, is F1 * 1.0594630^4 (where ^ means “raised to the power”), or F1 * 1.0594630 * 1.0594630 * 1.0594630 * 1.0594630.

Substituting our calculation of F2 into the pipe length equation, we have
L2 = L1 / sqrt(F1 * 1.0594630^4 / F1), or
L2  = L1 / sqrt(1.0594630^4)

So, to calculate the length of a pipe that sounds N semitones above your first pipe (where semitones below are negative numbers), the math works out to
L2 = L1 / sqrt(1.0594630^N)

Plugging in all the stuff above, L1 = 396mm and N (of the A) is 4:
L2 = 396 / sqrt(1.0594630^4)

Wow, that was boring! At any rate, now you can cut and tune all the pipes in your glockenspiel, using these two formulae:

  1. L2 = L1 / sqrt(1.0594630^N)
  2. Nodes at = L2 * 0.224
  3. Strike the chime at the center = L2 / 2.0

In my next post, I describe a build fail of the wooden frame. Making is not always as linear as it seems.


Nerd Christmas Tree

I’ve successfully assembled my second soldering kit: The Velleman MK130 ‘3D’ Christmas Tree.  It’s a set of blinking LEDs that sit atop a 9V battery… or you can add some long wires and hang it as a Christmas ornament.

At any rate, it was good practice for soldering, and the result is kinda cute.  See my YouTube Video of the Kit for the whole experience.

I figure I’m ready to build an Arduino proto Shield next!

Ah, the lovely incense of (lead free) solder

Since I’ve been doing Arduino work, I’ve accumulated a few board and Shield kits that I need to put together. I haven’t soldered since college, so I decided to brush up on my rusty skills by buying one of those little electronics project kits: a Velleman MK102 Flashing LEDs kit.

It turned out really well, thanks to my Hakko FX888D Soldering Station from SparkFun, and my QuadHands 3rd hand from Amazon. The circuit worked right away.

Check out the really, really boring video of the finished board blinking away at YouTube – whee!

The front of the board doesn’t look too bad; only a few parts pulled away from the board a bit:

Velleman MK102 kit
The component side of my finished Velleman MK102 Flashing LEDs kit

The back is the real giveaway that I’m a newbie: most of the soldering looks pretty good, but I see a couple cold solder joints, a couple dirty solders, and one pair of soldered points that are a bit too close for comfort – fortunately they didn’t short out.

Velleman MK102 kit, solder side
Solder side of my finished Velleman MK102 Flashing LEDs kit.

Not bad for a first effort, and on par with the handiwork on many cheap electronic gizmos you might buy. Next I’m planning to solder one of those little Flashing LED Christmas Trees, which has many more components. Then I think I’ll be ready to have a go at one of the Arduino board kits!

I’ve blocked Comment Spam… I think

Chirk Castle barred door
A barred door in Chirk Castle, England.

Comment Spam is the bane of blogs: fake comments that are nothing more than links to sites offering  high-fashion shoes, purses, and porn (curious set, no?)

I’d love to accept real comments from anyone who is not anonymous, but unfortunately Spam Comment robots happily provide fake identities. So I’ve had to restrict comments to people who have created an account on my site.

…but even that doesn’t take care of the problem. As this WordPress FAQ explains, the WordPress comment settings affect only future posts; existing posts are still targets for spam.

So now I’ve set up comments to work only for people who have accounts on this site, and have turned off comments for all my old posts.

Hopefully my new posts will welcome your comments, as long as you create an account with me. Sorry for the trouble; blame the Comment Spammers.

The Squirrels predict a cold winter

The Co-Presidents never put much stock in rural folks tales of very wooly caterpillars predicting a bad winter… until one year when we noticed a squirrel had made a huge pile of fir-cone nibbles, a few months before we were snowed in for a couple weeks.  A similar thing happened before the last bad winter: we noticed a squirrel tossing down hundreds of green pine cones, to stash the goodie-parts away for the winter.

So a few weeks ago when we noticed that a squirrel had dropped hundreds of these Douglas Fir cones onto our deck, a suspicion grew within us that this winter could be a doozy.

So here’s our prediction: 2014-2015 winter in the Portland Oregon area will be unusually cold.  There, we’ve put our bet down. Let’s see how winter turns out.

Fir cones on our deck foretell a hard winter
Fir cones on our deck foretell a hard winter

Light Up: a donating piggy bank

Arun Mota, a design student at Copenhagen Institute of Interaction Design, conceived of a piggy bank that donates a portion of your savings to a cause.

The project nicely ties together the cause (electricity for rural areas) and the form (a jar that lights up when you put coins in it). I also love the feasible simplicity and clarity of the mechanics of the piggy bank and the donation system. I want one!

Demonstration image of the Light Up project by Arun Mota
“Light Up” project by Arun Mota

Tim Hunkin: Brilliant artist, engineer, and maker

I first heard of Tim Hunkin when I watched his TV series The Secret Life of Machines: a whimsical but thorough explanation of how various devices, from elevators to fax machines, work. I was hooked.

More recently, I’ve been following Tim’s work at his site,  http://www.timhunkin.com/, which shows and describes his fantastic (and fantastical) projects. I love his animated collection boxes / vending machines. My all-time favorite is Nobby: a sculpture of a lifeboat man, who rattles his box and, on receipt of a coin, nods his head in benediction. It’s a nicely understated and sympathetic experience – I look forward to seeing it one day.

Tim Hunkin's animated collecting box named Nobby
Tim Hunkin’s animated collecting box named Nobby