Shallow Thoughts

An Arduino battery timer

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
[ 12:10 Oct 27, 2008    More tech/hardware | permalink to this entry ]

Un-Jamming an Epson C86

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
[ 13:12 Sep 13, 2008    More tech | permalink to this entry ]

Back from OSCON

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
[ 22:00 Aug 04, 2008    More conferences | permalink to this entry ]

Keyboard Cable by Rube Goldberg

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
[ 12:09 Mar 29, 2008    More misc | permalink to this entry ]