Shallow Thoughts
Akkana's Musings on Open Source, Science, and Nature.
Mon, 27 Oct 2008
I wrote in my OSCON report a few months back that I came home from the
conference with an
Arduino
microcontroller kit and just enough knowledge and software to make
LEDs blink. And so it sat, for a month or two, while I tried to come
up with some reason I desperately needed a programmable LED blinker
(and time to play with it).
But it turned out I actually did have a practical need for a
customizable programmable gizmo. One of the problems with
R/C combat
flying is that you're so focused on keeping track of which plane
is yours that it's tough to keep track of how long you've gone on
the current battery. You don't want to fly a lithium-polymer battery
until it gets so weak you notice the drop in power -- that's really
bad for the battery. So you need a timer.
My transmitter (a JR 6102) has a built-in timer, but it's hard to use.
As long as you remember to reset it when you turn on the
transmitter, it displays minutes and seconds since reset.
Great -- so all I need is somebody standing next to me who can
read it to me. Looking away from the sky long enough
to read the timer is likely to result in flying into a tree, or worse.
(The new uber-fancy transmitters have programmable beeping
timers. Much more sensible. Maybe some day.)
I could buy a kitchen timer that dings after a set interval, but
what's the fun of that? Besides, I could use some extra smarts
that kitchen timers don't have.
Like audible codes for how long I've flown, so I can make my own
decision when to land based on how much throttle I've been using.
Enter the Arduino. Those digital outputs that can make an LED
blink work just dandy for powering a little piezo beeper, and it turns
out the Atmel ATmega168 has a built-in clock, which you can read
by calling millis().
So I wired up the beeper to pin 8 (keeping an LED on pin 13 for
debugging) and typed up a trivial timer program,
battimer.pde.
It gives a couple of short beeps when you turn it on (that's so you
know it's on if you can't see it), then gives a short beep at 9
minutes, a long one at 10, shorter one at 11, and thereafter gives
(minutes MOD 10) beeps, i.e. two for 12, three for 13 and so forth.
Fun and easy, and it works fine at the field once I worked out a way
to carry it (it's in a camera bag hanging on my belt, with the beeper
outside the bag so I can hear it).
Fun! It could use better codes, and a pause switch (for when I land,
fiddle with something then go back up on the same battery).
Of course, in the long run I don't actually want to devote my only
Arduino kit to being a glorified stopwatch forever. I have further
plans to address that, but that's for a later posting ...
Tags: hardware, arduino, electronics
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12:10 Oct 27, 2008
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Sat, 13 Sep 2008
I turned on my printer to print out a form I needed to mail and it
emitted a nasty high-pitched noise ... not quite a squeal, but almost.
And it refused to feed paper more than about an inch at a time.
Pressing the paper feed button made it roll the paper about an inch
farther down, stop, and squee again. Another press, another inch,
stop and squee. Each time it seemed to advance the paper quite
smoothly -- it wasn't slipping, jamming or feeding at an angle.
How do you google for a weird high pitched noise? I tried a few
phrases in combination with epson c86 OR c84 OR c88
and hit several promising-looking URLs with domain names like
fixyourownprinter.com ... but every hit turned out either to be
someone describing a problem, then the discussion morphing into
a discussion of unclogging ink cartridges, or someone describing
a paper feed problem like mine and someone answering with
unhelpful advice like "you could fix the mechanism if you could
get the back panel off, but that's hard if you're not a printer
repair shop and printer repair shops charge more than the printer
is worth, so throw it away and buy a new printer."
I try to be green -- I recycle, turn off lights, try to use low
power PC and monitor, and I'll be damned if I'm going to throw out
a great big hunk of mostly nonrecycleable plastic every couple years
without at least trying to fix it.
Giving up on web searching, I unplugged the printer and started
pushing and poking at it to see what I could disassemble.
The back cover clearly was tucked into the two side covers ...
it clearly wasn't going anywhere until those side covers came off.
The side covers had several holes to the plastic piece underneath, with
arrows near them seeming to invite "push and slide". But there
didn't seem to be much consistency to whether I was supposed to push
the outer cover, or the inner tab, in the direction of the arrow.
I finally just ignored the arrows and used screwdrivers and pliers
to poke and compress and wedge and slide until I got the left side
cover (left as seen from the front of the printer) off.
The right side cover was more challenging -- I had all the tabs
loose, but the cover seemed to stick at a point near the front, near
the "Dura-Brite" oval. After twenty minutes of attempted finesse, I
switched to trying to force it (since the alternatives were to throw
the printer in the garbage or pay a repair shop more than the price
of a new printer). I heard two sharp CRACKs as of
plastic tabs breaking ... and the stuck front side popped loose.
Curiously, I couldn't find any obviously broken plastic inside; forcing
it was apparently the right and only way to get that side cover off.
Inside ... everything in the paper path looked fine. I pulled out an
errant paper shard that's been floating in there for about a year (I
knew right away when I fed that sheet of business cards with some of
the cards already removed that it had been a bad idea) but it hadn't been
touching any of the mechanism.
What's this on the left side, though? There was a tiny ink-smudged
piece of paper between one of the pulleys and its toothed belt.
Hmm. Doesn't look like it ought to be related, but it clearly
doesn't belong ... so I pulled it out.
I poked and prodded and shone flashlights for a while longer, but
couldn't find anything else. Darn! Well, just for the heck of it, I
plugged the printer back in and switched it on. No squee tone!
Hmm ... I fed it a piece of scratch paper and pushed the paper feed
key ... and the paper went straight through, no noise, no fuss.
Whee! I hooked it up to the computer and tried a nozzle
test (escputil -r /dev/usblp0 -mC86 -u -n) and it seems
fine! The printer is back in its normal place now ... sans side
covers, of course. I figure putting them back on so soon is just
an invitation for the problem to come back. I'll put them back on
eventually ...
The moral of the story is: don't let ignorance stop you from trying
to fix things.
Maybe the problem was that little piece of paper wedged in the wheel after all.
Or maybe, as I often suspect, sometimes hardware just gets lonely and wants
some attention ... and if you're willing to spend an hour dinking with it,
it doesn't matter how little you know about what's actually wrong.
All it really wanted was your attention.
Tags: hardware, printing
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13:12 Sep 13, 2008
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Mon, 04 Aug 2008
No postings for a while -- I was too tied up with getting ready for
OSCON, and now that it's over, too tied up with catching up with
stuff that gotten behind.
A few notes about OSCON:
It was a good conference -- lots of good speakers, interesting topics
and interesting people. Best talks: anything by Paul Fenwick,
anything by Damian Conway.
The Arduino
tutorial was fun too. It's a little embedded processor with a
breadboard and sockets to control arbitrary electronic devices,
all programmed over a USB plug using a Java app.
I'm not a hardware person at all (what do
those resistor color codes mean again?) but even I, even after coming
in late, managed to catch up and build the basic circuits they
demonstrated, including programming them with my laptop. Very cool!
I'm looking forward to playing more with the Arduino when I get a
spare few moments.
The conference's wi-fi network was slow and sometimes flaky (what else is new?)
but they had a nice touch I haven't seen at any other conference:
Wired connections, lots of them, on tables and sofas scattered
around the lounge area (and more in rooms like the speakers' lounge).
The wired net was very fast and very reliable. I'm always surprised
I don't see more wired connections at hotels and conferences, and
it sure came in handy at OSCON.
The AV staff was great, very professional and helpful. I was speaking
first thing Monday morning (ulp!) so I wanted to check the room Sunday
night and make sure my laptop could talk to the projector and so
forth. Everything worked fine.
Portland is a nice place to hold a convention -- the light rail is
great, the convention center is very accessible, and street parking
isn't bad either if you have a car there.
Dave went with me, so it made more sense for us to drive.
The drive was interesting because the central valley was so thick
with smoke from all the fires (including the terrible Paradise fire
that burned for so long, plus a new one that had just started up near
Yosemite) that we couldn't see Mt Shasta when driving right by it.
It didn't get any better until just outside of Sacramento. It must
have been tough for Sacramento valley residents, living in that for
weeks! I hope they've gotten cleared out now.
I finally saw that Redding Sundial bridge I've been hearing so much
about. We got there just before sunset, so we didn't get to check the
sundial, but we did get an impressive deep red smoky sun vanishing
into the gloom.
Photos here.
End of my little blog-break, and time to get back to
scrambling to get caught up on writing and prep for the
GetSET Javascript class for high
school girls. Every year we try to make it more relevant and
less boring, with more thinking and playing and less rote typing.
I think we're making progress, but we'll see how it goes next week.
Tags: oscon08, conferences, linux, travel, portland, hardware
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22:00 Aug 04, 2008
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Sat, 29 Mar 2008
Dave and I were helping out with replacing the keyboard on a friend's
computer. Isn't it funny how keyboards never come with cables that
are quite long enough to go from the front of a desk to the back,
down and around to the computer that sits underneath?
This particular desk has a backboard that makes the cable take a
more circuitous path than most, and when we unplugged the old
keyboard, we discovered that it was plugged in using an extension
cord.
And what an extension cord! It's a PS/2 to 5-pin AT plug
adaptor ... connected to an AT to AT extension cable ... connected
to an AT to PS/2 cable on the other end. Each of the three pieces
is yellowed with age, but to three different colors.
Unfortunately the mass spectrometer is on the fritz again so we
weren't able to establish accurate Carbon-14 dates for each of
the three pieces.
Tags: humor, hardware
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12:09 Mar 29, 2008
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