Project MOPTAWMy Own Personal Thing a Weekhttp://bandgap.rsnsoft.com/drupal/atom/feed2007-12-30T01:09:29-08:00MOPTAW 47: LED Color organ for an electric violinhttp://bandgap.rsnsoft.com/drupal/node/552008-05-02T19:24:45-07:002008-05-02T21:29:54-07:00machack
Porkshanks commissioned me to design an LED color organ driver for a functional art-piece modification of an electric violin, for Maker Faire. She herself had been commissioned to convert an electric violin to a tubepunk aesthetic, and was looking for a lighting effect more sophisticated than a plain glow. I built one that drives brightness based on loudness and huge based on pitch.
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Porkshanks commissioned me to design an LED color organ driver for a functional art-piece modification of an electric violin, for Maker Faire. She herself had been commissioned to convert an electric violin to a tubepunk aesthetic, and was looking for a lighting effect more sophisticated than a plain glow. I built one that drives brightness based on loudness and huge based on pitch.
An ATmega168 samples the output from the violin's pickup at around 4 kHz. It's capacitively coupled to a voltage divider to bias the violin's zero voltage to the '168's input midpoint. A digital highpass filter with a very low corner frequency removes the DC component from the input signal.
From there, the signal is split into two complimentary subbands, and a signal strength estimate is performed by grouping every 32 samples of each of the upper and lower bands, as well as taking an estimate of the total signal. The total signal strength estimate is then lowpass filtered and use to drive the brightness of the LEDs. The pitch is estimated by treating the high and low bands as coordinates, and taking the arctangent of their ratio. This resulting phase angle is the pitch estimate.
The informal justification is that a very low frequency tone will excite the lowpass filter almost exclusively, just as a very high frequency tone will excite the highpass filter. A midpoint tone will excite the two equally. What is important is the ratio between the two, with 0 mapping to a low tone, 1.0 mapping to the midpoint, and +inf for a high tone.
This only strictly speaking works for pure sinusoids. Harmonics and aliasing components will contaminate the estimate. Although the input circuit forms a lowpass filter, I didn't tune it to match the sampling rate. I chose a sampling rate high enough that aliasing components tend to be due to quite weak harmonics, and the amplitudes of even the unaliased harmonics are low enough that, for a violin at least, the mapping is actually quite good.
I'm working on a commission that calls for a 3-color LED to respond to audio input. With appropriate parameters, it produces a fairly convincing flame effect. Here it is inside an egg Naj made for entirely unrelated purposes.
I'm working on a commission that calls for a 3-color LED to respond to audio input. With appropriate parameters, it produces a fairly convincing flame effect. Here it is inside an egg Naj made for entirely unrelated purposes.
]]>MOPTAW 42: Spectroscopyhttp://bandgap.rsnsoft.com/drupal/node/532008-03-25T19:35:54-07:002008-03-25T20:03:07-07:00machackThis week was a research phase. I'm putting together parts for a spectrometer.
I just need some mirrors and I'm mostly set. I'm going with what is mostly a Czerny-Turner monochromator design, with two differences. First, the grating is a transmission grating, not a reflection grating, so the bottom half "flips around". Second, I'm using an imaging sensor rather than a single exit slit, so it's not actually a monochromator.
And here's a bonus photo I took of some lightbulbs through a diffraction grating. Incandescent on top, CFL on the bottom:
]]>This week was a research phase. I'm putting together parts for a spectrometer.
I just need some mirrors and I'm mostly set. I'm going with what is mostly a Czerny-Turner monochromator design, with two differences. First, the grating is a transmission grating, not a reflection grating, so the bottom half "flips around". Second, I'm using an imaging sensor rather than a single exit slit, so it's not actually a monochromator.
And here's a bonus photo I took of some lightbulbs through a diffraction grating. Incandescent on top, CFL on the bottom:
]]>MOPTAW 41: Accelerometer test harnesshttp://bandgap.rsnsoft.com/drupal/node/522008-03-20T00:22:52-07:002008-03-20T00:31:52-07:00machack
I'm working on a mostly super-secret project that requires accelerometer data. Phase one is characterizing the response caused by static acceleration due to gravity. The rotation stage is hooked up to a stepper motor. I have it turn one degree and pause for one second, through two full revolutions. The data is logged to SD card. This yields a series of sine waves for the three axes, although only two of them do much of anything interesting at a time. There's a lot of oscillation after each rotation step, which will need to be filtered out to get just the static response. A big thank-you goes to Lisa, who built the jig to attach the boards to the rotation table.
One of the input channels on the ADC was getting bad data. Turns out I lifted a pad while reworking the connector on the IMU board. Whoops. It's been since fixed.
]]>MOPTAW 40: Stacked and Dourhttp://bandgap.rsnsoft.com/drupal/node/502008-03-07T17:05:51-08:002008-03-07T19:45:02-08:00machackI present to you:
http://www.stackedanddour.com/
Quite some time ago I was at a restaurant with a friend. We got to talking about the waitress, who, we observed, was both busty and grim-faced. "There should be a magazine called Stacked and Dour", one of us said.
Later, a friend promised to pose if I put up a website, so I registered the domain, but didn't do anything with it. I finally put it up. It's not really a porn site.
Quite some time ago I was at a restaurant with a friend. We got to talking about the waitress, who, we observed, was both busty and grim-faced. "There should be a magazine called Stacked and Dour", one of us said.
Later, a friend promised to pose if I put up a website, so I registered the domain, but didn't do anything with it. I finally put it up. It's not really a porn site.
(Also, I did stuff the week ending 2/29, but I didn't write anything up. Maybe I'll back-fill at some point. I did vivisect an animatronic Frog, so maybe I'll post that for 39-in-retrospect.)
]]>MOPTAW 38: Thing-a-day week 3http://bandgap.rsnsoft.com/drupal/node/482008-02-22T01:02:08-08:002008-02-22T01:02:08-08:00machackThing-a-day stopped being fun, and I found myself rushing to find the bare minimum I could count, so I stopped doing it part way through the week. Here are the things I did do. I'll be back to regular MOPTAW schedule and content for the next entry.
]]>Thing-a-day stopped being fun, and I found myself rushing to find the bare minimum I could count, so I stopped doing it part way through the week. Here are the things I did do. I'll be back to regular MOPTAW schedule and content for the next entry.
]]>MOPTAW 36: Thing-a-day week 1http://bandgap.rsnsoft.com/drupal/node/462008-02-03T23:29:33-08:002008-02-03T23:29:33-08:00machackFor February I'm doing thing-a-day, so I'll be counting those for my weekly projects. Here's the first one: http://www.thing-a-day.com/2008/02/02/day-01-stellated-icosahedron/
]]>For February I'm doing thing-a-day, so I'll be counting those for my weekly projects. Here's the first one:
]]>Ferrofluid log: supplementalhttp://bandgap.rsnsoft.com/drupal/node/442008-01-31T14:20:30-08:002008-02-02T00:44:20-08:00machackWhat's ferrofluid? "A ferrofluid (from the Latin ferrum, meaning iron) is a liquid which becomes strongly polarized in the presence of a magnetic field. It is a colloidal mixture comprising extremely small magnetic particles suspended in a synthetic oil. The particles are coated with a soap or detergent to prevent them from clumping together." -- Wikipedia entry on Ferrofluid
]]>What's ferrofluid? "A ferrofluid (from the Latin ferrum, meaning iron) is a liquid which becomes strongly polarized in the presence of a magnetic field. It is a colloidal mixture comprising extremely small magnetic particles suspended in a synthetic oil. The particles are coated with a soap or detergent to prevent them from clumping together." -- Wikipedia entry on Ferrofluid
Where can I get some? United nuclear sells it on their chemicals page (search for MagnaView). You can also make it yourself
What can you do with it? There are various practical applications, but even more importantly, various awesome applications. Check out YouTube for a variety of videos.
]]>MOPTAW 35: Let me show you my ferrofluids!http://bandgap.rsnsoft.com/drupal/node/432008-01-26T19:55:39-08:002008-01-26T19:55:39-08:00machackAs promised:
Yes, this is cheating. Think of it as being like a "clips" episode.
]]>As promised:
Yes, this is cheating. Think of it as being like a "clips" episode.
]]>MOPTAW 34: I made you some ferrofluids... but I eated them.http://bandgap.rsnsoft.com/drupal/node/422008-01-21T23:07:41-08:002008-01-21T23:07:41-08:00machackWell, not quite. Unfortunately, not only am I late with this post, I also don't have video to show for it. The video is sitting on the camcorder, and I can't seem to find the mini-firewire to firewire cable to pull it off.
]]>Well, not quite. Unfortunately, not only am I late with this post, I also don't have video to show for it. The video is sitting on the camcorder, and I can't seem to find the mini-firewire to firewire cable to pull it off.
So, pretend you're looking at an electromagnet strong enough to make ferrofluid show its spines. I used a core of low-carbon steel, about 1" in diameter, wound with about 24-gauge enameled wire. The bench supply I was using was only good up to 3 amps, which wasn't enough to make much of an effect. I hooked it up to a 12v lead-acid battery, though, and that did the trick. Based on the voltage drop and coil resistance, I estimate it was pulling about 27 amps off the battery. That heats the coil up right quick, however.
I now need to experiment with different coil geometries to see if I can get something that produces an interesting effect in the fluid without overheating quickly. I also need to look into a higher-current bench supply. The battery doesn't last long between charges.
Also I need to get a cable for the camcorder soon. I have all kinds of rad video to post: the new year's party, laser interference patterns (testing a vibration isolation table), a high-voltage water bridge, and the ferrofluid of course.
]]>Fixed the LaTeX renderinghttp://bandgap.rsnsoft.com/drupal/node/412008-01-13T02:00:40-08:002008-01-13T02:00:40-08:00machackThe " /> rendering was screwed up, but should now be working.
]]>The rendering was screwed up, but should now be working.
]]>MOPTAW 33: Ferrofluidhttp://bandgap.rsnsoft.com/drupal/node/402008-01-13T01:46:19-08:002008-01-13T01:46:19-08:00machackLarger versions on flickr:
]]>Larger versions on flickr:
I played with ferrofluid this week. I was hoping to use an electromagnet to activate it. The ones I made this week weren't strong enough to do more than make it wiggle. But stay tuned!
]]>MOPTAW 32: New Yearhttp://bandgap.rsnsoft.com/drupal/node/392008-01-05T23:24:46-08:002008-01-05T23:24:46-08:00machackI went to a fabulous new year's party:
Since I helped set up and am a regular participant at the space running the party, I had a staff badge, which consisted of a piece of aluminum with a spray-painted logo. I wanted to make mine better.
Since I helped set up and am a regular participant at the space running the party, I had a staff badge, which consisted of a piece of aluminum with a spray-painted logo. I wanted to make mine better. , I superglued phosphorescent powder from United Nuclear over the logo portion, and put a couple layers of lacquer over it. In order to keep the glow charged, I mounted a couple of UV LEDs on stalks made of stiff wire covered with heat-shrink tubing. To keep the wires in place and generally make it awesomer, it had a squid-like "skin" Anne made for it out of an old sock.
The LEDs, in series, were powered via a Li-Ion cell through a Joule Thief step-up converter. This let a 3.7v cell power the 6.6v of voltage drop through the LEDs. Unfortunately, this ended up putting about twice the recommended current through the LEDs, so they died kind of quickly. Still, it was fun while it lasted.
Anne accidentally ran off with the photos and the original. So sad! I'll be off on a trip when she gets back, so it may bit a bit before I get the pictures.
]]>MOPTAW 31: Wireless Mesh Networkhttp://bandgap.rsnsoft.com/drupal/node/382007-12-30T01:09:29-08:002007-12-30T01:09:29-08:00machackMy Christmas present to Anne's family was to extend their wireless network to the guest house next door. I first tried boosting the power on their existing network, but that wasn't quite enough to push the signal usably into the house.
]]>My Christmas present to Anne's family was to extend their wireless network to the guest house next door. I first tried boosting the power on their existing network, but that wasn't quite enough to push the signal usably into the house.
I bought a pair of Linksys WRT54G routers. These were the most recent revision, v8. I had read some reports that at least some stock Linksys firmwares included automatic support for WDS, the protocol that enables handoff between base stations, but this didn't appear to be the case. I ended up installing the DD-WRT firmware because it appeared to have the most robust support for the most recent version of the WRT54G, which doesn't have as much flash memory as the older ones did. I put one of the base stations in the main house (next to the existing base station built into the DSL modem) and taped the other one to a window. There's only about 20% link quality between the two, but that's better than the 0-3% further inside the house.
I set up both routers with the same SSID, encryption keys, and channel. Since the existing DSL modem/router is already handling DHCP and routing, I set both to bridge mode and disabled their WAN interfaces. I gave each the other's MAC address and set them up as each other's WDS peers. There's a loss of bandwidth due to the relaying, but it's still enough to saturate the internet connection.
" /> rendering was screwed up, but should now be working.
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