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

  • Tour Easy + BOB Yak = Useful Cargo Capacity

    Tour Easy + BOB Yak Leaf Hauling
    Tour Easy + BOB Yak Leaf Hauling

    As mentioned there, I use a BOB Yak trailer to tote stuff that doesn’t fit into the panniers on my Tour Easy recumbent bike.

    We shred dry autumn leaves, bag up the chips, store the bags under a tarp beside the garage, and then Mary mulches the weeds to death in her gardens in the spring. I usually haul a pair of bags to the garden when we ride out for groceries: never waste a trip.

    The Yak’s rear fender is a nice stiff aluminum arch with stout steel stays, built to take exactly this sort of abuse. The trailer is utterly reliable and tracks perfectly: highly recommended.

    It does turn the ‘bent into a 12-foot-long vehicle, so urban assault riding is pretty much out of the question. On the other hand, nobody begrudges me a parking space of my very own. Which is a good thing, as puny little bike racks quake at my approach.

    This looks scarier than it really is, although having the center of gravity up that high does tend to make the trailer shimmy a bit over 20 mph… which speeds I reach only going downhill.

    Update: I have a pair of Nashbar cargo nets (their deep links rot quickly, so site-search for net) to hold bulky stuff in place. One normally does the deed, but some loads demand both!

  • Tone Encoding/Squelch vs. APRS Packet Reception Reliability

    We’ve been using ham radios on our bikes for years, but last year I put together an interface that connects a TinyTrak3+ GPS encoder to the helmet mic amp. This year I’m building two more, about which I’ll write later.

    The problem is that listening to APRS data bursts isn’t all that pleasant, although it’s bearable, but it’ll get much worse when we use 144.39 MHz as our intercom frequency so we can both talk and be tracked: we’d hear all the APRS traffic within digipeater range.

    Now, admittedly, talking on 144.39 isn’t standard. The local APRS wizards have given tentative approval, as we can’t figure out a better way to talk, give position reports, and not carry two radio / battery / antenna / electronics packages on each bike. As long as we don’t do a lot of yakking, we shouldn’t interfere with the digital traffic very much… and we don’t do a lot of talking while riding.

    So I figured I’d send a 100 Hz tone under the audio and enable tone squelch, so we wouldn’t hear packets from anybody else. We’d still hear each other blatting away, but if I set the TT3+ encoders to send a position report every 10 minutes, it ought to be bearable.

    The catch with this is that some receivers / APRS decoders can’t handle subaudible tones. I considered Digital Coded Squelch, but one of our radios doesn’t include that feature, alas.

    To get some idea of how tone would work with the APRS setup around here (which is where we do most of our riding), I set up an HT on the bench with the TT3+ and my interface. The antenna is an HF/VHF discone, indoors, on the basement floor, beside a window. The GPS receiver can see a slice of sky from its perch just outside the basement window under an awning. That’s about as terrible a setup as we have on our bikes: low power, bad antenna, obscured line-of-sight.

    Each test ran 10-14 hours, the TT3+ sent a packet every 5 minutes, and I checked the raw packet results on aprs.fi.

    With tone off and the TT3+ waiting for 3 seconds of audio silence before transmitting, 39% of the packets got through to the APRS-IS backbone.

    With tone on and, thus, the TT3+ unable to hear / avoid other traffic, 47% of the packets got through on one test and 42% on another. The higher rate was overnight, when (I think) there’s less traffic on 144.39.

    Putting the gadgetry back on the bike, parking it beside the garage, and letting it run for 5 hours on a Saturday afternoon showed that 81% of the packets made it to the backbone. Some of the packets were received by stations over 30 miles away, which probably coincided with the the closer receivers hearing transmitters hidden from the more distant ones.

    The only conclusion I can come to is that tone squelch isn’t going to hurt anything around here, where the APRS wizards have done a great job of getting the decoders to cope with subaudible tones. How it’ll work elsewhere is up for grabs, but we’ll burn that bridge when we come to it.

    And it turns out that the radios take about half a second to wake up and activate the audio output with tone squelch enabled, so we don’t actually hear the data bursts: they’re almost always finished and we may hear dead air for a fraction of a second. Because the TT3+ can’t do collision avoidance, we sometimes hear other packets from other transmitters before the squelch closes again, but it’s not objectionable. Whew!

    Update: with the TT3+ set to transmit every 3 minutes, it works fine!

  • BOB Yak Trailer: Storage Thereof

    Grocery Hauling Setup
    Grocery Hauling Setup

    Bicycles, in general, aren’t set up for heavy load carrying, so I use a BOB Yak trailer for groceries, garden goodies, recycling, dead PCs, and this and that and the other thing. It works surprisingly well, tracks nicely, and tends to push cars another half-lane to the left.

    Word: if you want plenty of clearance in traffic, haul a 20-pound propane cylinder in your bike trailer!

    Anyhow, storing the trailer is a bit of a nuisance, as it’s not particularly stable on its own and takes up a remarkable amount of floor space.

    BOB Yak on garage door rail
    BOB Yak on garage door rail
    BOB Yak hanging against shelves
    BOB Yak hanging against shelves

    I finally figured out that it would hang neatly from the garage door tracks, just beyond where the door stops at the top of its travel. There’s a set of shelves against the wall, filled with the usual crap found on garage shelves (well, maybe you don’t have beekeeping supplies, but you get the idea), so the trailer isn’t blocking anything really important.

    I lean my bike against those same shelves and the trailer hangs neatly between the seat and the fairing. The ladies’ bikes are just out of sight to the right.

    We have a two-car garage that’s the right size for one minivan and three Tour Easy recumbents…

  • Byonics TinyTrak3+ GPS Power Control

    GPS power from MOSFET relay
    GPS power from MOSFET relay

    The Byonics TinyTrak3+ GPS encoder has a “Power Control” output that can switch the power to a radio or GPS interface. J6 provides the interface: pin 1 = common, pin 2 = high active.

    With the “Power Switch” option enabled in the config program, you can set the number of seconds to allow the GPS unit to get up to speed before the next scheduled transmission.

    I glued a surface-mount MOSFET relay to the back of the PCB with urethane adhesive; it fits neatly between the DIP microcontroller’s pins with one output lead soldered to the 5V pad of J7. The other lead goes to the center +V pad; because the relay uses back-to-back MOSFETs, the polarity doesn’t matter.

    That replaces the normal solder bridge across J7 that provides power (on pin 4) to the GPS2 plugged into the DB9 connector. When the relay’s on, it connects the GPS to the power supply. When it’s off, the GPS goes dark.

    The relay input is an LED with a forward drop of 1.3 V max and requires 4 mA to turn on: figure 3.7 V / 4 mA = 925 Ω max. I kludged an 890 Ω resistor by paralleling (stacking!) 1.5 k and 2.2 k resistors; you could probably use anything near that and it’d work fine.

    The relay is an OMRON G3VM-21GR1, part number A11171 from Electronics Goldmine, but I suspect any teeny little solid-state relay would work. The max on resistance is about 1 Ω and the receiver draws about 65 mA. I measured about 20 mV of drop, so the actual resistance is a lot lower than the spec.

    I initially set the power-on delay to 10 seconds, which seemed to be OK: the GPS (green) LED would blink a few times, then go solid. Alas, the warm-start spec for the Byonics GPS2 (see the GPS3 for details) receiver is really 38 seconds, average, and it was definitely producing bogus position data. So I set the delay to 60 seconds and we’ll see how that works; early reports indicate the coordinates still have plenty of jitter.

    [Update: 60 seconds is iffy. 90 seconds seems to work pretty well. A bit of rummaging says that the satellites broadcast their ephemeris data every 30 seconds, so 90 seconds allows for two complete update cycles. Maybe 100 seconds would be even better. Some old background info for Garmin hand-held receivers is there.]

    It’s obviously a tradeoff between accuracy and battery life. This is for use on a bicycle and, believe me, I don’t want to tote a huge battery!

    If the control signal was low-active, then you could use a cheap PNP transistor as a high-side power switch.

    The white/orange wire routes regulated 5 V through an otherwise unused pin to the homebrew interface that combines the GPS data with helmet mic audio. The tiny rectangle is a 1 µF cap that helps cut down digital noise. There’s no need for a connector on that end, as it’s wired directly to the interface circuit board inside a small enclosure.

  • Fireproof Door: FAIL

    Warped fireproof door
    Warped fireproof door

    OK, this one is baffling. It’s a fireproof (well, more likely, just fire-retardant) door between a lounge and an equipment / elevator room.

    It looks like they made the door by casting something like concrete inside a standard lauan hollow-core door.

    What’s truly odd is that the concrete (or whatever) filling is also warped, convex side outward. The door edge strip with the latch is straight as an arrow, having separated from both of the facing panels and the concrete core at the bottom.

    Did the outside of the door get wet in some way that didn’t soak the surrounding room?

    We’ll never know…

  • Aligning to a Hole With a Defocused Laser Spot

    Defocused Laser Spot on Hole
    Defocused Laser Spot on Hole

    When you’re aligning to an edge or scribe mark, you want the laser spot as small as it can possibly be, so you tune for best focus.

    To locate the center of a hole, you first find the edge, then move toward the center by one radius… so you must know the diameter, too. It’s tricky to find an edge exactly on the X or Y axis, which means you generally resort to successive approximation. I did something like that there with good results.

    If you defocus your laser aligner to produce a spot slightly larger than the hole, you can simply position the hole under the beam to produce a nice bright ring. Adjust the focus to make the spot barely larger than the hole and you can get pretty close to the center without any messy arithmetic.

    Now, should you happen to own a real laser aligner, you might actually have a nice-looking defocused spot. My homebrew Orc Engineering aligner, as shown there, starts with the beam from a chip laser in a hacked carpenter’s level, so the defocused spot is rather, mmm, ragged, even after passing through the not-very-restrictive aperture behind the lens.

    With the lens in the spindle, though, I can spin it at a few hundred RPM and persistence of vision blurs the beam into a nice, symmetrical disk. Jog to center the disk around the hole, twiddle the Z-axis position to adjust the focus / size / blobbiness, jog more slowly, tune for best picture, and it’s all good.

    This obviously doesn’t produce jig-boring quality alignment, but, then, I’m not doing that sort of work. In the picture, I’m enlarging a 4-40 hole molded in a Pactec case to fit a 6-32 screw. Normally I’d do that by hand on the drill press, but this time I also had to enlarge the counterbore at the top and figured I’d use a quick G2 with an end mill after I had it aligned for the drill.

    Maybe everybody else knows this trick, but I was delighted to find that it actually works pretty well…

  • Electronic Ballast Shoplights: So Much For Efficiency

    Just picked up a batch of electronic-ballast shoplights from Lowe’s, motivated by a 10% off card they sent a while ago. Not a killer deal, but it evidently got plenty of folks into the store on a Sunday morning.

    The new lights don’t claim much about their abilities, other than “Electronic Cold Weather Start (0° F)” and that the reflector sizing requires T8 (1″ dia) fluorescent tubes. One would expect an electronic ballast to have a decent power factor and improved efficiency.

    Because I’m that sort of bear, I opened one up to see what was inside. Here’s the ballast:

    Electronic Ballast Dataplate
    Electronic Ballast Dataplate

    Although the fixture is sized for T8 tubes, the ballast would be perfectly happy with T12s. Similarly, the box insists on F32 tubes, but the ballast is OK with F40s.

    I thought a comparison with one of my old magnetic-ballast fixtures would be of interest, so I hitched up the Kill-A-Watt meter and ran some comparisons.

    The results…

    Amp Watt VoltAmp PF
    Old magnetic ballast
    F40T12 0.64 60 76 0.79
    F32T8 1.11 80 126 0.62
    New electronic ballast
    F40T12 0.75 47 89 0.53
    F32T8 0.77 49 91 0.54

    The electronic ballast has a much lower power factor and thus much higher current. The box & ballast don’t say anything about power factor correction and, wow, there sure isn’t any. The power company hates gadgets like this…

    I cannot compare the brightness because the F40 tubes are several years old, but it’s interesting that the electronic ballast runs both tube sizes at essentially the same power (just as the dataplate indicates, sorta-kinda). The magnetic ballast really cooks the piss out of the smaller tubes, though… or it’s dumping a lot of energy into the ballast. Hard to say.

    The T12 tubes are rated for 3000 lumens & 20 k hours. The new box of T8 tubes I got a while back are 2800 lumens and 24 k hours. Frankly, I don’t believe any of those numbers, particularly given the actual power consumption: it looks like either ballast runs them at just 75% of their rated power.

    Anyhow, these were the cheapest shoplights in stock; I bought eight of ’em, because I’ve been replacing one dead fixture every month or two for the last year. I’d like to think I’d get a better ballast if I spent twice as much, but to a good first approximation the additional cost seems to have gone into black plastic trim and a burnished-chrome exterior finish; not what I need in the Basement Laboratory.

    I wish the boxes were more forthcoming so you didn’t need to perform exploratory surgery.