Archive for February, 2009

Polishing Aluminum: Practice Run

Sunday, February 22nd, 2009

Last weekend I picked up some aluminum block at The Yard, an aircraft (and miscellaneous) surplus and supply store in Wichita, for an upcoming project. I also picked up aluminum polishing supplies at Autozone based on the experienced recommendation of the shift manager with a very shiny motorcycle outside.

Here’s a first pass at cleaning and polishing a block using materials I had around the house. The polished surfaces really highlight which stages of sanding needed more work — at a minimum, not skipping from 220 to 600 grit (I don’t seem to have any 400) and continuing up to 1500 — which was largely the point of this test. No need to point out my errors; I already know.

Tomorrow night I’m having supper at a machinist’s house, and I hope he may be able to do some surface cleanup for me before I redo this block and tackle the other three.

Aluminum blocks and plates

Aluminum block, end honed with diamond file

Aluminum block, face sanded with 180 grit

Aluminum block, face sanded with 220 grit

Aluminum block, face and end sanded with 660 grit

Aluminum block polished with Turtle Wax Polishing Compound

Aluminum block polished with Mothers Mag & Aluminum Polish

And by the way, the Mothers polish has a smell like vaguely lime-scented floor cleaner that takes me straight back to a Colorado Springs Popeye’s Chicken restaurant on vacation in the late 1970s. Smell is the sense with the strongest link to memory.

Scooba Second Impressions

Tuesday, February 10th, 2009

Scooba 5900

My first impressions of Scooba were based on not yet having the official Clorox cleaning solution and running with vinegar water. I got my shipment of the Clorox solution yesterday and ran four cleaning cycles on the bathroom floor. New notes:

  • I had left both batteries fully charged but off the charger for a week, and Scooba reported one as completely dead and the other didn’t make it through a full cleaning cycle. Looks like I’ll need to keep them on the charger and/or use them more frequently.
  • The Clorox solution smells good! (Remember that vinegar is my grounds for comparison . . .) It smells like a cross between some kind of detergent and your widow grandmother’s soap-scented bathroom.
  • The Clorox solution seems to clean a little better than the vinegar water — that is, leaves the floor noticeably cleaner. Scooba made visible progress on the dark marks in the faux grout lines on our vinyl floor.
  • The Clorox solution puts a shine on the floor! I don’t consider it perfect or done, but the bathroom floor looks way nicer than it did before getting Scooba or after running with vinegar.

Note to other secondhand Scooba owners: Buy the Clorox!

Storage Storage for Samples Storage

Monday, February 9th, 2009

In the past, I’ve tried several techniques for organizing my small quantities of IC samples (and “purchased samples”). I have enough different ones and each needs so little space individually that I don’t really want to dedicate parts bins to them.

IC samples in different containers

I’ve tried putting them in pockets in a three-ring binder, leaving them in the open shipping carton, and leaving them lying around on my workbench in their packages.

None of these have worked particularly well for me.

Mainframe Backup Tapes

At work, we have a large collection of “3490″ mainframe backup tapes, and they’re kept in large racks without the plastic cases the tapes ship in. In the IT environment, large sets of disks and tapes are referred to as “storage;” so the empty plastic cases and the racks the tapes go in are “storage storage,” right?

We had a few empty tape cases left, which were of no use to us and which I took home. We’ve also retired our mainframe and pruned our backup collection, so we have a number of empty racks and rack cases sitting around. It looked like an opportunity to salvage discarded materials and improve my electronic parts storage.

Tape Packages for Electronics Parts

Stacked tape cases with ICs

Last night I put most of my samples into empty tape cases, and it worked quite well. At Wal-Mart I found some Avery labels that are compatible with #5366 (2/3″ x 3 7/16″, called “File Folder — White”), are ultra-opaque, are supported by the label feature in OpenOffice, and fit nicely onto the approximately 1″ x 4.25″ case spines.

Racks (Or Not)

The cases have ridged edges and stack very nicely, but I was hoping to get them into a rack for easy “random access” to individual boxes.

Data tape case doesn't fit into tape storage rack

Unfortunately <grunt>, the racks <grunt shove> weren’t made to hold the cases <curse shove>, just the tapes <growl>, and the cases don’t fit <sigh resignation>.

Boxed tape cases with ICs

I still have some of the boxes that the tapes originally shipped in, but this isn’t necessarily an improvement over just stacking the cases. They’re still sort of “latched” together in the boxes, and it’s almost more difficult to pry a case out of a full box than to balance a stack of cases whilst removing a lower one.

I’ll keep looking — hopefully there’s a rack out there that fits the cases, that someone doesn’t need any more, that I can save from the landfill, and that I get for free. :-)

Speaker to Preamp Adapter for Jeremy

Friday, February 6th, 2009

Jeremy and I have been kicking around ideas we’d like to see in a 1U rackmount audio mixer. I’d like to be able to mix my synths and digital piano together with another audio source so I can play along with a CD to figure out the keyboard part, without having to have separate speakers for the keyboards as I do now. Jeremy would like to be able to listen to his own selection of background music while he’s playing (some) video games at his entertainment system and projector. I’d like to be able to record my synth output into my iBook without having to disconnect and recable everything — and without necessarily recording audio from the CD I might be playing along to.

Once we figure out the number and types of inputs and outputs we want, we’ll go shopping and see if such a mixer already exists at a price commensurate with our needs. If so, buy. If not, talk about building.

Meanwhile, we got distracted by Jeremy’s receiver. Some of his audio sources are digital, so we thought we’d need his receiver to decode them before going to an analog mixer. And his receiver doesn’t have an effects loop or tape monitor, so we’d need to use line or preamp outputs and an outboard amplifier for at least his main speakers. And he doesn’t have preamp outs, so I started talking about tapping his speaker outputs and at about that point this degenerated into a game of “okay can we just get his receiver to feed through one of my SAE A502 amps and power his speakers.”

Speaker to preamp adapter, top

The answer, of course, is yes.

And by the way, all of his digital audio sources have analog outputs right next to them that we can use for our analog mix, so all of this was completely pointless. :-)


LM34DZ Fahrenheit Temperature Sensor

Monday, February 2nd, 2009

This started as notes I made to myself long ago for the LogoChip, but they apply equally to the Arduino A/D converters.

The LM34DZ is a temperature sensor in a TO-92 case available from All Electronics for $2.50. It has the handy characteristic of reading an output voltage that directly corresponds to Fahrenheit temperature in a ratio of 10mV per °F. That is, at 70°F it reads 70 * 10mV = 700mV.

LM34DZ Fahrenheit temperature sensor

With a direct output voltage (rather than the varying resistance that many thermal probes provide), it’s perfect for hooking to a microcontroller A/D input. So, how to convert the A/D reading back into Fahrenheit temperature?

Well, the sensor reads 10mV (or .01V) per °F. Microcontroller A/D converters tend to have 5V input and read 1024 steps over the 0-5V range.

1024 steps / 5V ≈ 205 steps / V


(.01V / °F) * (205 steps / V) ≈ 2 steps / °F

Thus you can get a “maybe close enough” approximation with code like

tempF = analogRead(lm34Pin) / 2;

With a conversion error of +2.4%, this’ll get you within a couple of degrees at room temperature — close enough to make some macro-level observations about whether it’s getting warmer or colder for a physical computing project. Since the stated accuracy is only 1°F anyway, that’s not too bad.

If you need a more accurate conversion, you’ll need to use floating-point arithmetic if you have it (which the Arduino doesn’t [correction: does]) or find a fixed-point arithmetic library if you don’t. Or if your integer variables are large enough (at least 17 unsigned bits for temperatures up to 127°F, 18 bits up to 255°F), you can rearrange the order of calculation like so:

tempF = (1024 * analogRead(lm34Pin)) / 5;

Scooba First Impressions

Sunday, February 1st, 2009

I love how my Roombas help keep pet hair picked up with a minimum of effort; and I’ve been fascinated by the idea of the Scooba, iRobot’s wet-mopping robot, since it was announced. I recently picked up a used 5900 in very nice condition on eBay from a wonderful seller who even included a spare battery.

Scooba 5900

I want to start with a pictorial overview, since I hadn’t seen enough Scooba pictures to understand how different it really is from the Roombas, then proceed to a few comments about my experience with it so far.