The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

Author: Ed

  • Chipmunks Discover Agriculture

    Chipmunk atop sunflower
    Chipmunk atop sunflower

    One of the sunflowers in the garden started swaying wildly, despite having no breeze at all. I though it was a goldfinch plucking seeds, but a quick look through the binoculars showed a brown furry tail hanging below the topmost seed head, about five feet off the ground.

    Mary reports that this is one of five sunflower plants growing in a tight group near the garden fence; she thinks a chipmunk’s seed stash sprouted. This could be the start of something big: next thing you know, they’ll be planting seeds and harvesting crops!

    As we watched, the critter’s cheeks became more and more distended.

    Chipmunk stuffing cheek pouches
    Chipmunk stuffing cheek pouches

    Eventually, however, gluttony overcame common sense.

    Getting the last seed
    Getting the last seed

    Seconds after the shutter clicked, the sunflower head disintegrated, depositing the chipmunk on the ground with a rustle and a soft plop.

    No damage done, we’re sure, and that critter’s pantry should be stuffed full in short order. Next year Mary will probably do some extensive sunflower culling to get room for the rest of her crops!

    And, yes, the title is a riff on Bears Discover Fire

  • APRS SmartBeaconing Parameters for Bicycling

    Setting relatively prime beacon times for the GPS-to-APRS trackers on our three bikes worked quite well, but I wondered how much better SmartBeaconing would be. The trick is getting the numbers right for typical bicycling speeds.

    Here’s some settings (from the TinyTrack3+ config program display) that seem to work reasonably well…

    SmartBeaconing Parameters
    SmartBeaconing Parameters

    The general idea is to beacon every 10 minutes at rest and about three / mile in motion.

    The only time I hit 3 MPH is up a really nasty hill, the likes of which I avoid with all due diligence. On the other end, 24 MPH is pretty much as fast as I can go for any length of time; faster, certainly, on downhills, but those are rare & precious commodities on most rides around here. The Slow and Fast parameters control both ends of that range. The beacon rate increases linearly below the Fast speed: 180 seconds at 12 MPH, which is roughly what I used for the constant-time setting.

    Note that the Rate parameters are actually periods. Rate is thing/time, period is time/thing. The period varies as 1/speed, while the rate varies directly with speed. See the SmartBeaconing writeup or the TinyTrak3+ doc for the algorithm.

    The Turn Slope parameter is the most confusing. It has units of degrees/MPH degree·MPH and serves to modify the Min Turn Angle so that you must turn more sharply at lower speeds to generate a beacon. This works better for vehicles with a wider dynamic range: our bikes tend to stay within 5-20 mph and a factor-of-four doesn’t affect the basic angle very much at all.

    My track through a residential area shows pretty good “Corner Pegging” for those settings and, in any event, it’s much better than the simple every-three-minutes beaconing I’d been using before. On the other hand, this is in a low-RF-traffic area with a digipeater about a mile away across the Northway, so very few packets get clobbered.

    APRS Track with SmartBeaconing
    APRS Track with SmartBeaconing

    Perhaps setting Turn Slope to 240 degrees/MPH degree·MPH with a Fast Speed of 24 MPH and a Turn Angle of 10 degrees would be slightly better. At top speed the minimum turn angle would be 10 + 240/24 = 20 degrees and nose-pickin’ speed relaxes the angle to 10 + 240/6 = 50 degrees. On the other hand, that track looks pretty good as-is!

    One problem with three bikes in close proximity (the track above is just me) is that we’ll all be turning at about the same time and, thus, sending beacons almost simultaneously. This will take a while to sort out, given that many beacons never make it to a receiver…

    [Update: A correction shows why the units aren’t what I expected.]

  • Getting More Clearance While Bicycling

    Some cyclists complain that motorists don’t give them enough room while passing. That’s less of a problem for recumbent bikes, but this gets me a lot more clearance:

    Bike trailer with propane tank
    Bike trailer with propane tank

    There’s one section of very nice and totally gratuitous 6-lane highway (NY Route 55 near the NYS DOT Region 8 HQ; I think they’re just showing off) where drivers normally edge over to the left side of the right-hand lane where I’m riding. With a 20-lb propane tank lashed to my bike trailer, most folks have no trouble whatsoever with a double lane change into the far left lane…

  • How to Impress a Contest Judge

    Every now and again, I’m asked to judge a technical contest of one sort or another. Let us assume, for the purposes of this discussion, that you are participating in such a contest and I’ve just begun to look at your entry…

    Rule 0: Send a PDF

    The contest rules will tell you what document files they expect; typically, it’ll involve some version of Microsoft Word. Why they do that, I cannot say, but Word documents aren’t really suited to read-only document distribution. Not to mention, some of us don’t have MS Word installed…

    In addition to those files, also include a PDF of your final document file so that when I open it, it’ll look exactly the way you intended. MS Word documents tend to look weird on any PC other than yours, particularly if you have any odd fonts or formatting options turned on. If you can’t figure out how to produce a PDF, install OpenOffice and use the direct PDF export; that’ll also show you how weird MS Word can appear in a different word processor.

    Don’t waste time on a fancy layout, but do pay attention to the basics:

    • Images must fit inside the margins of a single page
    • Use simple fonts that are large enough to read
    • Avoid complex tables and drawings: use PNG images instead

    Hint: ask a friend to review your submission, ideally a few days before you plan to submit it. Take any comments you get very seriously.

    Rule 1: Tell Me What You Did

    The first two paragraphs of your documentation must tell me:

    • What your project does
    • Why that’s a great idea

    That should take, at most, half of the first page.

    You have two paragraphs to catch my attention; sweat bullets over those words!

    Hint: If you can’t summarize what your project does in one sentence, maybe you don’t have a good project.

    Rule 2: Let Me Judge How Easy (or Hard) It Was

    Going on at length about how easy the project was produces the impression that maybe there’s not enough effort in there to justify a few kilobucks of prize money. Conversely, kvetching about how hard you worked indicates that you bit off more than you can chew.

    Let the project tell the story. A good project requires more than a few evenings of effort and, believe it or not, the amount of effort will show up in your description, even if you don’t mention it at all.

    Hint: If you’re trying to be funny, it probably won’t work.

    Rule 3: Use Good Pictures

    Examine all the pictures with a hyper-critical eye.

    • If they’re blurry, delete them and take them again.
    • If you think a picture might be out of focus, it is.
    • If there is the slightest trace of doubt in your mind about the quality of a picture, delete it and try again until you get it right.

    When you get the focus right, ruthlessly crop your pictures. Hint: I don’t need to see the crap on your workbench or the dirty laundry in the corner of your room. Devote all the pixels to your project!

    When you don’t care enough to invest a few minutes getting a good picture, the rest of your project is probably sub-optimal, too. Don’t bother to submit it, OK?

    Crisp pictures can’t sell a weak project. Blurry images rarely accompany a good project.

    Hint: That big LCD on the back of your camera is there for a reason. Use it!

    Rule 4: Support Your Claims

    If you claim to have built a multi-node, RF-networked, high-bandwidth, vibration sensor measurement system, then you must include data supporting your claims. Otherwise, I’ll assume you don’t know what you’re talking about or haven’t actually gotten it working, should my back-of-the-envelope calculations indicate there’s not enough RF bandwidth / range / compute power to pull it off.

    You must convince me that your project does what you claim!

    Hint: Should you claim to have built a snake-armed robot that balances atop a ball while serving drinks from a refrigerator, a video demonstrating it in action is worth a thousand words.

    Rule 5: Don’t Hide a Skeleton

    You may encounter a serious problem that simply can’t be fixed before the contest deadline. When that happens, explain what you intended to have happen, what the problem is, and what you propose as a solution. As long as the problem is secondary to the project’s intent, that’ll be fine.

    For example, if your project involves half a dozen different sensors and you just can’t get the humidity sensor working, explain your debugging efforts and the results.

    Conversely, if it’s a networking project and you can’t get the Ethernet code working, then your entire project just went down the drain and you shouldn’t submit it. I can generally tell when a project simply isn’t going to work, so your efforts to hide the corpse won’t gain you any points.

    Hint: Start your project early enough so that when something goes wrong, you have time to fix it.

    Rule 6: Use the Specified Hardware and Use It Hard!

    The contest is generally about using some particular microcontroller or chunk of hardware. Your project should fully utilize that chip: make sure you read the manual and exploit a whole bunch of its unique features.

    Hint: a project where all the action takes place in a Javascript routine or another, entirely different microcontroller probably isn’t making good use of the specified chip.

    The Bottom Line

    If you’ve got a good project and describe it well, you’re probably in the money. Plenty of other entrants will ignore these suggestions and wind up on the bottom of the pile.

    Fair enough?

  • APRS Beaconing: On Being Relatively Prime

    I ran into an amusing situation on a recent family bike ride with our GPS-to-APRS trackers running: my ladies were transmitting a few seconds apart. As a result, I had to listen to a pair of very short data bursts in quick succession throughout the whole ride.

    Under normal circumstances that doesn’t happen, because I set the TinyTrak3+ trackers to delay during and wait a second after a voice PTT that collides with an automatic beacon. Somehow they never managed to delay an APRS beacon to knock the synchronization off kilter.

    So I tweaked the automatic transmission intervals to make us relatively prime: 179, 181, and 191 seconds. That’s close enough to the original 180 seconds as to make no difference, while now ensuring that we won’t collide with each other for very long even if we should get aligned.

    An alternative is SmartBeaconing, which I’ll turn on in a while after I collect a bit more data.

    A useful table of primes is there.

    If you have some spare CPU and power, you can join the Great Internet Mersenne Prime Search and help find new primes, albeit ones much larger than I need…

  • Yaesu FT-857 Front Panel: Up-Armored Plug

    The  remote cable for the Yaesu FT-857 I have in the car terminates in an 8-pin modular plug. The connector body has a cutout for the round rubber (?) insulation around the cable; it’s not set up for a standard flat 8-wire network cable. However, the cable makes a right-angle bend immediately outside the Front Panel to fit inside the confines of the remote mounting case, which pulled the insulation out of the connector.

    Connector with displaced insulation
    Connector with displaced insulation

    The electrical connections are fine, but that can’t last. I finally got around to armoring that bend to (I hope!) prevent any problems. Contrary to what you might expect from my proclivity to blob epoxy on everything, I blobbed on hot-melt glue to hold the wires in place, as well as turn a bit of the cable into a rigid body. Even in a hot car, this ought to work fine…

    Connector with hot-melt glue
    Connector with hot-melt glue

    I put some ordinary adhesive tape on the back of the Panel, butted up against the connector body, to keep the glue out of the socket and off the (back of the) Front Panel. That prevents the connector from becoming one with the Panel.

    Pause while the glue solidifies, release the latch and pry the connector+glue off the tape with a small screwdriver, trim the excess glue, then peel the tape off the Panel. The connector snaps into place just like it should and the wires no longer have any freedom of motion.

    Here’s what the modified connector looks like in all its glory. The cable really does bend downward slightly beyond a right angle in order to fit into a recess in the Front Panel.

    Finished connector kludge
    Finished connector kludge

    This isn’t suitable for a connector getting a lot of the old in-out in-out, but the Front Panel remains in place for months at a time and this should delay the inevitable failure.

  • Railway Infrastructure: The Rot

    Saw this while riding along a rail-trail route west of Philadelphia. Evidently they left the catenary support structures standing over the trail to carry the (still energized!) power lines, but the I-beams webs across the trail have rusted completely through.

    Rusted railway catenary support
    Rusted railway catenary support

    Verily, rust never sleeps… I wonder if they ran diesel locomotives along this part of the line?

    The beams across the active railway seem to be in fine shape.