cliff

upgraded DIY mask

home sewn mask with added shape-holding wire
We have some hand-sewn masks made of two layers of cotton. I modified two with the addition of wire in the top hem, allowing the wearer to bend the wire to fit the bridge of the wearer's nose. This significantly increases the mask's ability to seal to the wearer's face when inhaling, and may improve filtering when exhaling. (The positive pressure of exhaling tends to lift any mask that isn't held by adhesive or external force.)
Steel wire between 22 and 30 gauge, or copper wire between about 18 and 26 gauge should work for this. I used enameled copper magnet wire, 24 gauge, because that's what I have on hand. If you cut the wire at a sharp angle, you can preform holes in the fabric by separating it with a sewing pin, then gently press the wire through the preformed hole. I used the space between my fingernail and fingertip to back up the fabric, so the wire would protrude through, and then I could move along to the next one. I ran the wire back and forth, a running stitch, with about 6mm of space between each hole. It seems to work pretty well.

There is currently a lot of dispute about the effectiveness of DIY masks. I've found sources that say two layers of the sort of cotton used for t-shirts is about 50% as effective as an N95 mask, while one layer of tight weave quilter's cotton over one layer of flannel is somewhere near 80% as effective as an N95. https://www.npr.org/sections/goatsandsoda/2020/04/03/825639323/scientists-probe-how-coronavirus-might-travel-through-the-air has an extended discussion about current views on aerosol and droplet spread of viruses, which is poorly understood.

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cliff

(no subject)

My manager's been gone for three weeks and I've gotten a lot done at work and had a fairly fun time doing it, so that's nice.

The rice cooker blew out its own fuse again. This will be the third one I've replaced in this cooker, and the one before it also blew out two. I'm pretty confused by this. I've measured the wall voltage and it's approximately correct. It's possible the factory used a very marginal cheap fuse, but my replacement fuses were not cheap and (I calculated) are about 15% more than the surge current through the cooker.
At least I bought a lot of replacement fuses... Now I kind of wish I'd also bought a fuse socket and installed it.

Edit to add: rice cooker problem explained. I couldn't get an exact replacement so I got the type of fuse we use at work, without thinking too deeply about the use case. It turns out that the fuse being that close to the heating element means it needs to be a metallic case fuse with crimped connections. Soldered connections not only don't work, the solder has dissolved the adjacent wire.

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cliff

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Today's work project was a fun bit of learning. My coworker pulled a waveform off an oscilloscope. Not a picture of the screen, but the actual digitized data. Neither of us had any idea just how many points modern oscilloscopes can generate. He put the waveform in Excel, which promptly truncated it because Excel can only hold a million rows. So he showed up at my door.
I wrote something in C, and refamiliarized myself with malloc(). By some weird coincidence, what he wanted was half something I wrote yesterday (look for discontinuities) and half something I wrote a year ago (and stick them all in a specific dense format) so I managed to build him something pretty quickly, that with a bit of adjustment, could handle his four million line long text files and smash them down into 10,000 lines of relevant information. He was thrilled by it. (Now to see if I can somehow get that appreciation advertised upwards...)
I also thought of a possibly patentable idea. It's not a money maker, but it's the kind of thing my company would like to have locked up, so I'm going to try to find someone who appreciates weird ideas and see what it would take to have the company pursue this.

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cliff

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I ran a test for about six days straight, that generated 300MB of data or so, that I needed to filter down. My first filter, a simple delete-unnecessary-junk excel macro, pared that down to 50MB. But then I had a problem, that I'm still trying to handle.
I have four independent variables, that I'm sweeping through.
For each in (a-list):
For each in (b-list):
For each in (c-list):
For each in (d-list):
do stuff and measure stuff.

That's somewhere between 100K and 1M data points. I'm not really sure.
The issue is that at some point in each D sweep, an event happens, that results in a measurable outcome, and I have to figure out what everything else was, in the measurement before the event happened. This is complicated by sometimes happening before the first measurement (in which case there simply is no answer) and sometimes happening after the last event (again no answer) but once everything is in a giant excel spreadsheet, it's very difficult to tell a conditional formula or macro "hey only pay attention to events that happen within a d-sweep, not ones that happen at the boundaries between a, b, or c sweeps." Sometimes the event happens multiple times during the sweep, like it's in its no-event state, then in its event state, then back to no event, then back to event. All the things I've managed to write so far look at the overall pile of data, and trigger off every no-event-to-event transition, regardless of multiple events, of across-multiple-sweeps events, blah blah.
When I get done filtering I have a bunch of sparse columns: thirty or fifty blank rows followed by a row full of stuff. It took me a while to figure out how to condense that down. (In excel, the result of a formula is always some value, even if it's "" or #N/A or whatever: it may look empty but it is not empty, so I had to mess around a little to figure out how to choose all contents except for numbers and then delete those.)
Then I have this big mass of condensed, somewhat good data, only maybe 2000 lines of stuff or so, that I have to go through by hand and choose which ones to delete because they're clearly bad data, and then I have to go through that, and break it down by one of the sweep criteria and graph it.
There are so, so many places for mistakes of the copied-the-wrong-value sort here, and so many places where I have to make judgments about what constitutes good or bad data.
I'm trying to apply some basic statistics, stuff like throw away everything more than 3 sigma out, for instance. But I'm not sure that's valid. I'm not sure my assumptions about outliers are good, or about duplicates. My coworker, who might have better ideas, keeps looking at these giant masses of data, and saying "that's interesting" and getting off on tangents about how I'm measuring all these things and never answering my questions about data quality. My manager keeps sending me email asking me for finished analyses but never answers my questions about what constitutes good assumptions. (I've just started sending him my analyses with all the questions in there, so he has to read them to get to the conclusions.)

This is stuff I somewhat love. I suppose if I include all my questions and detail all my assumptions, that's the best I can do. It'd be nice to have more direction. But it's interesting learning a lot about data quality.

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cliff

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Every time it gets really windy (meaning once a week or so) the flapper on the oven hood vent starts clanging, as gusts of wind suck it open briefly and then it falls closed again.
Tonight while doing some other stuff I decided to fix it.
The problem with vent lines like this is that they're supposed to be airtight, so all the pieces fit together with positive overlap, meaning you can't just slide a piece out. It's held on both sides. So I had to drop the microwave from the cabinet it's screwed into, to get the space to get the flapper loose. Unfortunately, the hole in the cabinet the vent goes through interferes with the microwave being rotated down by the bracket against the wall, which I'd forgotten.
The process should go: lower microwave by about 2cm.
Pull upper vent hardware upwards, loosen the screw on the flapper, extract the flapper bracket.
It was a lot more difficult than that.
I wrapped some tape around the flapper itself, to dampen it, and [personal profile] threemeninaboat found some adhesive foam and put a bit of that on, and I went to put everything back, and twisted and bent the side part of the vent system outwards so I could see in and make sure the flapper worked correctly.
It closed all right (my concern, as I'd bent the bracket it's in, during extraction) but I noticed it only opened halfway. Somehow, it hits against the inside of the upper vent section, which is an adapter that goes from a 2" x 6" rectangular opening to the 5" round vent line that goes up and out the side of the house.
Well, I can turn the flapper around so it swings the other way.
Except the bracket that holds it is a one-way bracket: it only bolts to the top of the microwave in one direction, because it has slide tabs to hold it down, on one end, and just a sheet of metal on the other end with a slotted hole to screw it down.
This is why I have calipers and a milling machine.
So now both ends have tabs and slotted holes, and the bracket is in reversed and I've verified that it fully opens (which makes the fan quieter) and closes.

This weekend involved an awful lot of house maintenance.

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cliff

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I went into work today to find out that my manager is taking three weeks off for family medical leave starting today. He didn't say anything about this to anyone yesterday.
I'm working on building a whole bunch of wrappers so software language A can call a big binary blob written in software language B. Last time I did this, it took me a week longer than I'd anticipated to get it working, for a large variety of reasons. (The API documentation was wrong, I didn't start asking for help or pointing out that I was going to have trouble meeting my deadline until I was right up against it, and the target hardware documentation was flat-out wrong about things like how to correctly power it.) So this time around I decided that I'd get it working before the "when are you going to have this done?" discussion even came up. I've figured out how to automate it, so I set that off and running and when it finished I emailed my manager that I had a good start on the software for our next project, that as of last Friday was my number one priority that nothing should distract me from.
He emailed me back almost immediately to ask me how an entirely different project, that was my highest priority last Wednesday, was going, and mentioned at the end of the email that he'd decided to cancel the project for which I was writing this software.
I turned to my coworker and said "hey, did you know your next hardware project has been cancelled?"
He sat there gaping like a fish for several seconds. I was all "I guess you didn't know either."

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cliff

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I'm reupholstering the Spitfire seats. When I took one apart, amidst the half-wastebasket-quantity pile of broken-down foam, I also found a business card for a place that repaired MG's. The telephone number on the card was a seven-digit number, which probably means it was 1970's. There was also a 1974 penny in the seat.
Getting the seat cover off was a pain. There's a big piece of foam glued to the seat's steel tubing structure. It has a horizontal slit in the middle of it. There is a flap on the vinyl cover that goes through that slit and then clips to the frame further down, to hold the concave surface of the seat back against the foam. The clips are very easy to put on but extremely difficult to remove: they're like binder clips with tiny teeth that grip the fabric, only they have no little wire loops to remove them. They simply press on, but there is no simple way to remove them.
Similarly, the recliner function of the seat is controlled via a lever, and removing it to get the seat covering off was really difficult. Good thing I bought a gear puller years ago.

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cliff

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I stayed home sick today because I felt awful, although I can't really say I was contagious or anything.
That gave me time to go to Boulder and get a key for [personal profile] threemeninaboat's bike locker at the train station, the first locker reserved on the open-next-week line, and then physically verify the key's function, while also verifying that the lock does not in fact work on the door latch mechanism they've provided.
I also spent some time installing lock hardware on doors, because several of the doors have never had the right keys in the whole time we've lived here and when someone locks one of those doors it can be a serious hassle to get back through it.
This led to the discovery that there is no door sweep on the door between the garage and the house. There's a 10mm wide gap beneath it. That's about the same size gap between the garage door and the concrete.
No wonder we have a mouse problem.
I never thought to check, because the previous owners had carefully installed double-layer seals all the way around the door, as they did on every other one, to help prevent mice getting in.
It now has a nice custom-sawn piece of redwood that exactly fits in the space. Tomorrow that'll get bolted in place on the bottom of the door, when I have the energy to take the door off its hinges, and I'll put a commercial adjustable sweep behind it to air seal it as well as mouse sealing it.
As I was working on getting the parts together to fix this, I noticed the garage door opener no longer closes correctly.
This house needs some burnin' down.

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cliff

(no subject)

Tonight's project. You know that thing in the bottom of a dishwasher that goes around and around? Well, mine now just goes up, once, and then doesn't do anything at all.
So I'm trying to figure out how to build a little retaining ring to reinforce the fingers were supposed to hold it in place but have now apparently worn out.

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