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.

Month: October 2010

  • Turtles on a Log

    If there’s anything to reincarnation, next time around I’m going to put in a request to be a Staff Turtle at the Vassar Farm Environmental Station.

    Vassar Farm Turtles
    Vassar Farm Turtles

    Taken with my Casio EX-Z850 pocket camera, underexposed 2/3 stop to avoid blowing out the highlights even more. This is a dot-for-dot crop from the middle of a much larger 8 MP image, crisped up just slightly. Terrible results, but it’s better than the big camera I didn’t drag along on a guided geology tour (which ended with a generous handful of fine clay from the stream a bit further along).

    And, yeah, I know the whole reincarnation thing says you get what you deserve, not what you want. On the other flipper, nobody really knows how it all works, so I’m not losing hope.

  • New Cutting Board: Adding Feet

    So Kohl’s sent Mary a killer deal coupon and we bought some odds and ends, including a new cutting board to replace the decades-old one that I’ve been flycutting clean every few years. Evidently bamboo is the new Right Stuff for cutting boards; it’s certainly eyeshattering.

    The thing spent the last few days soaking up a slathering of canola oil, in the hope it won’t soak up other juices.

    Recess for cutting board foot
    Recess for cutting board foot

    The instructions say to store the board standing on end so it dries properly. Evidently you’re supposed to hang it from the ring screwed into one end, but a corresponding hook (not supplied) just doesn’t doesn’t have a place on our counter / cabinet / backsplash. However, we could stand it up, leaning against an under-cabinet shelf next to the toaster oven, if only it wouldn’t slide away.

    This calls for some aftermarket tweakage!

    So I hauled it to the Basement Laboratory Woodworking Wing and installed a pair of silicone rubber feet in little recesses.

    I grabbed a 7/16-inch end-cutting end mill in the drill press, because even the manual mill doesn’t have enough height for the board on end and the drill press doesn’t have enough reach for a Forstner bit without fiddling around with the emergency drop stopper clamp. The drill press does have a good vise and an XY table, so I got it pretty close to dead center on the third dark stripe from each edge.

    The feet are about 1/4 inch tall: I went down half that in the hopes they wouldn’t bump off quite so easily.

    Silicone foot in cutting board
    Silicone foot in cutting board

    But that didn’t quite work: the adhesive on the feet doesn’t grip the rather porous endgrain bamboo nearly well enough: a foot popped off after a day. I added a layer of Genuine 3M double-stick foam tape to the feet and that’s holding just fine.

  • Arduino Mega: Voltage Regulator Heatsink

    The Arduino Mega has an SMD voltage regulator soldered to a copper pad connected with thermal vias to a similar pad on the bottom surface. The datasheet says the (roughly) 10×10 mm copper pad sets RθJA=55 °C/W, more or less; probably a bit less with the double-sided setup.

    It’s the chubby black slab snuggled up just to the right of coaxial power input jack. The four vias on each side go to an isolated copper pad under the solder mask on the other side.

    Arduino Mega voltage regulator
    Arduino Mega voltage regulator

    The board draws about 75 mA with nothing fancy on the I/O pins, so the regulator dissipates half a watt with a 12 VDC input supply. Figuring an ambient of 30 °C, the junction temperature is ticking along at 50-60 °C.

    That’s all well and good, but my rule of thumb for semiconductors is:

    • If you can’t hold your thumb on it for any length of time, it’s too damn hot.

    That regulator fails my rule of thumb even before I start adding LEDs and other doodads.

    A bit of rummaging turned up an old Thermalloy sample box with a DIP heatsink. A dab of quick-setting epoxy and there it is:

    Arduino Mega regulator with heatsink
    Arduino Mega regulator with heatsink

    Now, I’ll grant you there are a number of things wrong with that approach, but my thumb is much happier. If it gets unhappy, I’ll just crack that puppy off and stick something larger in its place.

  • X Server 1.18 vs Wacom: Back to the Mainline

    As mentioned there, I had to use the Arch Linux linuxwacom-bamboo-cth-ctl package because X Server 1.8 discarded all the carefully tweaked HAL baggage and the existing xf86-input-wacom package wasn’t yet compatible with the new server.

    That worked fine, until the most recent X Server tweak killed the Bamboo driver (which I hadn’t manually updated). As I expected, though, the new xf86-input-wacom package works just fine, so I can discard my manual workaround.

    Having recently tweaked the tablet coordinates to keep the pointer out of the gutter, I first thought I’d killed something… but that would happen instantly, not after a while. The key was looking in /var/log/Xorg.0.log to find this gem:

    [  3447.599] (II) LoadModule: "wacom"
[  3447.638] (II) Loading /usr/lib/xorg/modules/input/wacom_drv.so
[  3447.651] dlopen: /usr/lib/xorg/modules/input/wacom_drv.so: undefined symbol: dixScreenOrigins
[  3447.652] (EE) Failed to load /usr/lib/xorg/modules/input/wacom_drv.so
[  3447.652] (II) UnloadModule: "wacom"
[  3447.652] (EE) Failed to load module "wacom" (loader failed, 7)

    Removing the bamboo package seems to have wiped out the udev rule that creates the /dev/input/wacom symlink. Adding that back in, as described there, solves that problem. Again.

    The evidence in /var/log/Xorg.0.log looked like this:

    [ 52121.754] (**) Option "Device" "/dev/input/wacom"
[ 52121.754] (EE) xf86OpenSerial: Cannot open device /dev/input/wacom
        No such file or directory.
[ 52121.754] (EE) Wacom - stylus: Error opening /dev/input/wacom (No such file or directory)
[ 52121.754] (II) UnloadModule: "wacom"
[ 52121.754] (EE) PreInit returned NULL for "Wacom - stylus"
[ 52121.754] (**) Option "Device" "/dev/input/wacom"
[ 52121.754] (EE) xf86OpenSerial: Cannot open device /dev/input/wacom
        No such file or directory.
[ 52121.754] (EE) Wacom - eraser: Error opening /dev/input/wacom (No such file or directory)
[ 52121.754] (II) UnloadModule: "wacom"
[ 52121.754] (EE) PreInit returned NULL for "Wacom - eraser"

    Everything is logged somewhere: the evidence is out there!

  • C Constants Aren’t Automatically Promoted

    Quick, what’s wrong with this code snippet…

    #define MAX_INTERVAL	(60*1000)

unsigned long int LoggedTime;
unsigned long int NowTime;

byte LogNeeded;

... snippage ...

LogNeeded = (NowTime >= (LoggedTime + MAX_INTERVAL));

    Yeah, that constant up there should look like this:

    #define MAX_INTERVAL (60*1000ul)

    Took me a while to figure that out. Again.

  • Trinity Rules: LyX and LaTEX Setup

    The preamble turns on line numbers for proofing; remove those lines to turn them off.

    \usepackage{ragged2e}
\usepackage{lastpage}
\usepackage{url}
\usepackage{dvipost}
\usepackage{breakurl}
\usepackage[labelfont={bf,sf}]{caption}
\usepackage{listings}
\usepackage{color}
\usepackage{lineno}
\linenumbers
\renewcommand{\bottomfraction}{0.7}
\pagestyle{fancyplain}
\fancyhf{}
\lhead{\fancyplain{}{Trinity College Home Robot Contests}}
\rhead{\fancyplain{}{2011 Rules}}
\lfoot{\fancyplain{Modified \today}{Modified \today}}
\cfoot{Copyright 2010 by Trinity College}
\rfoot{\fancyplain{\thepage\ of \pageref{LastPage}}{\thepage\ of \pageref{LastPage}}}
\RaggedRight
\dvipostlayout
\dvipost{cbstart color push Blue}
\dvipost{cbend color pop}

    There’s no obvious documentation for the Document → Settings  → PDF Properties → Addition Options values, but these make the crossref links look better:

    urlcolor=blue,linkcolor=blue

    For what it’s worth, LyX is still the right hammer for this job, although when something goes wrong, the error messages are truly oracular…

    Memo to Self: no line numbers in the final version!

  • Arduino Mega: Mounting Standoff and Screw

    The Arduino Mega has four, count them, four mounting holes in a more-or-less rectangular pattern around the edge of the board. Three of the four have enough room for standard pan-head 4-40 screws. The fourth hole is squeezed between two pin-header sockets, to the extent that no screw in my collection will fit.

    Screw on Arduino Mega board
    Screw on Arduino Mega board

    Having a lathe, however, makes this situation no big deal… and this time, I put the Sherline drill chuck in the 3-jaw because I wanted to, not because the 3-jaw was stuck. In truth, the lathe chuck simply won’t grab a 4-40 screw at all.

    Turning down the screw
    Turning down the screw

    I had that pointy right-cutting tool in the holder, so that’s how I cleared off the burr on the backside of the head.

    The chuck did grab the hex standoff just fine, though, and the final result looks like this…

    Modified standoff and screw for Arduino Mega
    Modified standoff and screw for Arduino Mega

    For future reference, the turned-down sections are 0.180 inch in diameter; call it 4.5 mm. The snout on the standoff must clear the pins,so it’s 0.100 inch or 2.5 mm long.