I needed an app that I could use to test XQueries. I couldn’t find a free one online, so I figured I’d just write it. Put the XML source that you want the query in the bottom window, your query in the text field, click the button and away you go!

I haven’t tested anything about it other than those things. Your milage may vary.
Released under the GPLv2.

Source code (zip, 41kB)

Intel binary (zip, 45kB)

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Unsuspecting security camera

Well, as a (perhaps welcome ) deviation from the spectrum analyzer posts, I’ve spent a little time working on repairing a security camera I’ve been hanging onto for a while.  I’ve been toying with the idea of installing it near the radio control flying field as someone in the club knows the owner of a nearby business.

The problem with the camera is that it has trouble switching from nighttime mode to daytime mode.  At night, it is sensitive to Near Infrared light (such as what is transmitter from your remote control).  During the day, however, this sensitivity makes the colors look strange.  To cope with this, they have a filter that slides in front of the lens for the daytime.  This filter binds, and because of this, the camera is always in nighttime mode.  I decided to go ahead and disassemble the camera to try to fix it.  My motto:  If it’s broke and out of warranty, take it apart!

Removing the lens

You can (kinda) see in this photo the image sensor.  This metal mount can move forward and back to accommodate different lenses and adjust their focal length.

Bottom cover removed

Removing the bottom cover reveals the power conversion board.

Removing the top cover

Removing the top cover reveals the PCMCIA slot.  This camera is kinda cool in that it can accommodate either a memory card or a wireless LAN card in this slot.  Also, there is an ethernet port on the back.  It has an embedded web interface that allows the control of camera functions and viewing live video.  Apparently, there is the ability to get some information from the serial port, but I haven’t found any information about it.

Front lens mount

Like I mentioned before, the front lens mount can be adjusted front-to-back.  The black screw near the top of the frame is used to secure the mount.  More to the right of the frame, the spring is used to press the mount against a set of wedges that control the depth setting.  The 4-pin connector goes to the lens iris, which is kinda like the aperture of a still camera.

Lens mount disassembled

This is the front of the camera disassembled.  The image sensor is still attached to the camera frame.  The black piece of plastic is the filter module, and the other piece is the metal frame for mounting the lens and adjusting the focal length.

Filter module

This is the device causing all the trouble.  The slight green tint in the left frame is the IR block filter, and the right is clear.  The motor is a small gear-head motor attached to a worm gear.  The worm gear has very shallow cuts in it.  The spring pushes down on a small plastic follower.  The whole system is intended to allow the worm gear to continue turning even if the system is jammed.  I think this is so that limit switches aren’t necessary.  I figured that the problems I’m having are due to excessive friction, which would cause the frame to remain static while the worm gear turns.  My first thought was to place a little petroleum jelly on the sliding surfaces.  I re-assembled the front of the camera and found that the problem remained.  However, I noticed that when the lens mount was all the way against the camera it would stick.  I could then solve the problem by keeping the lens not-quite against the camera.

Lens mount disassembly

Before re-assembling the camera, I decided to lubricate the adjustment assembly.  The black plastic ring on the right includes the adjustment wedges.  The middle ring is the precision-machined lens mount with a channel for the plastic ring.  The punched metal piece on the left completes the assembly.

Anyway, I put the camera back together.  It works great now.  I’m a little embarrassed to admit that the problem was simply that the lens can’t be in the closest setting for the filters to work.  At least everything went back together without a hitch.

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IF Amplifier cooling down

I’ve decided to hold off posting spectrum analyzer modules until they’re complete.  I’ve been collecting tons of pictures along the way, so hopefully the post for each module will be interesting and visually appealing.  With that in mind, I can’t post about any of the modules with the exception of this one.  For whatever reason, my kit didn’t come with any voltage regulators, and this is the only module besides the mixers from my last post that don’t use any.  The IF Amplifier, as the name implies, amplifies the Intermediate Frequency on the analyzer.  I made a simplified version of the block diagram from Scotty’s site.  I’ve also indicated the modules I’ve finished in green.

Block diagram, green modules are completed as of this post.

As you can probably see, there’s a lot to be done.  Luckily both DDSs, the Log Detector, ADC, Control Board, and one PLO are done once I get some parts to replace the missing ones.  I also need some parts for the Master Oscillator.  Once that (actually quite small) order comes in, I’ll be almost finished with the boards.

Anyway, back to the amplifier.  I was one of the first people on an order of boards back in August ’08 because I agreed to look-over a new revision of the design files.  Of course, by having me look them over essentially guaranteed that there would be errors.  As it happens there was an error on this board.  The engineering change order (ECO) is luckily quite simple, the only problem was that a short section of the border was missing.  Here is a photo of the completed fix:

Fix for the slight error,

You should be able to see that along the border there is some solder wick saturated with solder bridging the gap, and connecting to the capacitor.  Also, on (at least) the 2 resistors (R3 and R4) there are tiny balls of solder.  These happen during the reflow stage when a bit of solder squeezes out from underneath the device.  I haven’t gone over the board picking all these out yet in this photo.  I think it’s important to remove all of these because they may cause shorts.  Also, you may be able to see a slight, shiny, residue around everything.  This is the solder flux that’s included in the solder paste.  I remove this later with some 99% rubbing alcohol.

Completed IF Amplifier

This is the completed amplifier board.  There are actually 2 amplifiers here, mirrored.  In practice, the output of one will be the input of the other.  This serves to roughly double the gain.  Finally, notice on the right side, that many of the parts have been omitted.  On the schematic, Scotty simplified this section.  Technically, he has 2 zero-ohm resistors (basically jumpers) in addition to the capacitor.  I chose to just jump the capacitor across and leave the resistors out.

Anyway, I enjoyed building this one.  I hope you’ve enjoyed reading about it.  I can’t wait to finish the other ones!

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Mixer 2 completed and verified against schematic

I’ve verified each of the 3 mixers that I need for the spectrum analyzer.  The one above is mixer 2.  The schematic for this mixer is available from Scotty’s site.

Mixer 1 verified against schematic

I’ve also verified mixer 1 against the schematic.  There have been 2 optional revisions posted that aren’t included on mine.  I’m going to add them later, but only if necessary.

Mixer 3 verified against the schematic

Finally, mixer three is complete, and verified against the schematic.  This one isn’t strictly needed for the spectrum analyzer, however it is necessary for the tracking generator.  A tracking generator is a module that generates a signal that matches what the analyzer is tuned to.  This is useful for tuning filters, or other passive devices.

I’m missing some parts that I need to complete the control board.  I hope to get replacements soon, so I can begin testing some of these modules…   Stay tuned!

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A while back I bought a spectrum analyzer kit.  It can display waveforms in the frequency domain from 0 to 1000 Mhz.  I haven’t worked on it for a while, but I’ve decided to start working on it again.  If you’re interested in more information, there is a webpage for the analyzer by the guy who designed it, and there’s a Yahoo group, also. If you’re really-really interested there is a group buy open (until the 28th of march 2010) here.  Anyway, I’m sure it’s of limited use to my usual readers (thanks, friends & family! [oh who am I kidding, most of my family doesn't read this ]), but it may be useful to others working on the kit.  I’ll post the “annotated” CAD images for each board here, and add images of the completed boards when I finish them.  Who knows, it may be interesting for someone.  Also, I’ll include my thoughts and observations while building these boards.  Finally, not all the boards that come with the kit include annotated layouts, so I’ll have to dig around and figure out what they do and what to put on them

Log Detector:

Master Oscillator:

Analog-Digital Converter

Control Board:

Direct Digital Synthesizer:

Phase-Locked Oscillator:

Mixers:

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Picture in picture video

In this video, I’ve tried to synchronize video from a camcorder with the in flight camera.  I think it turned out really well.  I wish I knew how to make the canvas larger in iMovie so I could put the video side-by-side.  If you select the highest quality (480, I think) and make it full screen, I think it looks pretty good.

This video is from Tom and I trying to fly in some kind of formation so I could record his plane in flight.  It was very challenging because my plane is a lot faster than his.  I was flying on the brink of a stall most of the time while he was full-throttle.  There’s a moment where we almost had a midair.  We didn’t, so no harm.

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Comparing antennas

I’ve finished building the first (and my first) Yagi antenna for the Kadet video downlink.  I mentioned in the first video post that a new, and better, antenna would help greatly. I was able to find some designs online that fit my needs.  The major constraint that I had to deal with is the impedance issue.  Nearly everything amateur radio related is 50 ohms, and nearly everything video related is 75.  The cheap Yagis paper written by Kent Britain, WA5VBJ, has a 75 ohm 421 Mhz antenna intended for amateur television (ATV).  My transmitter is 434 Mhz, but I figured it would be close enough.  The great thing about these designs is that they can be built using supplies from a standard hardware store.  The elements are made from #10 bare copper wire, and the beam is wood.

Completed antenna

An interesting characteristic of antennas, and RF in general, is that to get a stronger signal you often have to make compromises.  A Yagi works by increasing the directionality to increase the signal.  Unfortunately, because my plane is going to be flying around, I can’t be too directional.  To get better results, without making things worse, I decided to only use the reflector and “driven element”.  By  eliminating the “directors” I hope that I can get the best possible results. (If you’re confused by this “director”, “reflector”, and “driven element” gibberish, the best place to look is the wikipedia article.  But all that is necessary for this discussion is that the reflector is behind the driven element [which connects to the transmitter or receiver] and reflects the signal forward, and the directors go in front and focus the signal into a narrower beam).

Feed line soldered

There were some problems during construction that I should mention to help others wanting to try something like this.  The antenna designs specify that the feed cable should be soldered directly to the driven element.  This should work great on traditional 50 ohm radio cabling, such as LMR or RG-type cables.  These cables have copper braid shield around the circumference.  With the 75 ohm cable used in video, often made as cheaply as possible, a loose aluminum braid is used as the shield.  This is a major problem that I had to deal with.  It took me a while to even understand why the braid wasn’t soldering.  I think I assumed that the braid was made of tin.  After a few hours of searching, I discovered it was aluminum.  Aluminum oxide forms almost immediately and can’t be soldered to, so even sanding the wire doesn’t help.  There are solder pastes and fluxes that help, but I wasn’t interested in waiting for something to be shipped.  My solution, if you want to call it that, was to mechanically attach the braid to some other wire that can be soldered.

In the first image of the post, I’m comparing the new antenna versus the others I used earlier.  When the Yagi was installed, I rotated the antenna 360˚in azimuth to get an idea for how directional the antenna really is.  There wasn’t much of a change in signal quality, so it isn’t very directional.  If the transmitter were further away it may have been more dramatic.  I am motivated to build a few more antennas, maybe with 1 and 2 directors to see which is better.  With that said, I’m pretty satisfied, and I’m hoping for good weather this weekend.

b.t.w: Just to dispel any fears that the shield is shorted to the center conductor, as it appears in the above photo, it was, and I fixed it.  Here is a photo of the feed point as it was when I tested it.  Also, notice that I got my driven elements and directors confused when I wrote on the board

Another view of the feed point

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Flying video

The weather sucked, but I was able to get out the the field this morning. I recorded about 17 minutes of video in total.  In the embedded clip, I edited out the majority of the static.  I’m a little disappointed that the signal quality is so poor.  I found a site that has some cheap Yagi antenna designs in 50 and 75 ohms.  I’ll probably try to build one this week and see how it goes.

More information about the camera is available in these posts, if you haven’t already seen them.

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Painted to match

Taking advantage of the crummy weather, I decided to paint the camera module to match my plane.  I didn’t just do it for the aesthetics, no really, I swear.  Actually, the real reason I painted it was to prevent stray light from making annoying reflections on the inside of the window.

Masking the window

The first thing I had to do was get an idea of the size and shape of the opening that would be needed.  I was able to measure it by looking at the video output and marking with a sharpie just outside of the camera view.  Once I had all the sharpie marks, I tried to make the shame smooth and symmetrical.  Since I had to mount the camera low in the module, as discussed in this post, the opening is low, and very parabolic.  I then covered the whole top of the window with masking tape and by shining a light through the bottom traced the sharpie line with a hobby knife.  Removing the excess tape left a nice mask for the opening.

Prepped for painting

With the opening masked, I sanded the window to give the paint the best chance at adhering.  It is apparently a little hard to find plastic spray paint (like Krylon fusion) in silver, so I had to use some general purpose kind.

Outside paint

I think the paint on the outside of the window turned out O.K.  There is a little dust and lint marring the finish, but it turned out not to matter much.  I also wanted to paint the inside with a matte black finish to minimize the chance of reflections from light that is still able to get in through the smaller opening.  I used a similar approach to the technique for the outside.  I placed masking tape on the inside of the window and shined light in from the other side.  I again traced the outline with a hobby knife.

Inside painted

For some reason, I really like the way this turned out.  It’s all pretty dark in there, and should minimize reflections.  I also painted the base of the module to match.

Camera module base painted

I think everything came together nicely.  I really like the finished look, even though I was pretty sure that it was going to look weird.  As I mentioned earlier, the lint on the outside paint didn’t matter.  I put masking tape on the front of the window to protect it while I painted the inside, and it lifted part of the paint when I removed it.  This gave it a strange effect, and I’m not sure whether I like it or hate it.  Katie says it looks cool, so I’m leaving it for now.

There should be good (enough) weather this Saturday, so hopefully I’ll have some video to post!

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Camera installed with Transmitter

I’ve just finished building a camera module for my Kadet.  When I was building the plane I knew that I was going to try and put a camera and transmitter approximately where the pilot’s head would be in a real plane.  That means a couple of things:  First, it’s pretty cramped up there with the flight pack, speed control, and motor.  Second, it’s a bit of a dirty secret, but forward visibility is usually not so great in most planes.  I tried to mount the camera as high as possible, but the front of the lens keeps hitting the glass.  I was able to get most of the view clear, but there is a margin on the bottom of the frame that is obscured by the wooden frame.  I will probably install some LEDs there to monitor battery charge, current, etc…

Outer frame of camera module

To build the outer frame of the camera module, I traced the shape of the wooden windshield onto a piece of acrylic.  After cutting it out I traced the inside of the fuselage onto balsa.  I cut out two side pieces and just glued them onto the acrylic.  I had to cut a notch into the back side of it to make room for the dowel that the wing rubber bands stretch over.  You can see how it fits in the first photo that I posted.

Camera mounted on bottom plate

I made a bottom plate by tracing the outer frame onto a piece of balsa.  Then, I took some balsa stick and made some uprights.  After drilling holes for the screws I soaked some thin CA into the sticks to keep them from splitting.

Camera module complete

The image above is the completed camera module.  At this point, there aren’t any electronics other than the camera module.  If you look really close, you can see the hole in the top of the windscreen on the top-left (the plane’s right).  This is for the video transmitter’s antenna.

Camera module schematic

The schematic for the camera/transmitter circuit is pretty straightforward.  The main consideration is that the camera and transmitter require different voltages.  The camera works best around 12 volts, and the transmitter uses 9 volts.  I only wanted to use one battery, so I had to make a voltage regulator.  I used my old standby, the LM317.  I also wanted to be able to adjust the transmitter voltage, so I added a potentiometer.  The transmitter came with a RCA plug and the camera had a BNC plug on a long cable.  I wanted to get rid of all this extra bulk, so I cut them off and connected them using the circuit board, also.

RCA Bunny ear antenna

The transmitter works on 433.92 Mhz, which is surprisingly hard to find in consumer products.  The obvious reason is that it’s in the amateur radio band.  But, 433.92 is actually channel 59 on cable.  This means that you can use a commercially available USB TV tuner to receive the video.  With that in mind, I gathered a few antennas to try.  The above photo is an antenna I bought to try.  It’s a VHF/UHF type from radio shack, I think.  I just went for the cheapest available.  I also looked for some antennas with “preamplifiers”, but I haven’t found any that amplify the 400 Mhz band.

Whip antenna

I also tried a whip antenna from an old 900 mhz wireless video system.  It’s not tuned anywhere near 400 mhz, but I’ve been lucky before.

I embedded a YouTube video of me walking around the house using each antenna.  The bunny ears are much better than the whip antenna.  The good thing about the whip is that I may be able to make another whip that is tuned correctly.  If the weather’s good tomorrow, I’ll probably try it out.  I’m pretty excited!

Update:  There have been a few successful flights recorded with the downlink.  The first video was pretty static-y, then I made a new antenna, and now the videos are much better.

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Ready to fly at the BCRCC Polar Bear

I’m back from the third (and fourth) flight, and it keeps getting better!  On Friday (New Years Day) I went to the BCRCC (Benton County Radio Control Club) “Polar Bear” event.  Basically, the idea is: On new years day, rain or shine, everyone comes and flies something.  There is a raffle for all those that fly.  I brought the Kadet, mostly because that’s the only plane I have, and the tiny Blade mSR that I got for X-mas.

Micro-heli flying

The Kadet’s second flight was somewhat uneventful.  Flying during an event invariably leads to crowded skies, because I didn’t have the runway to myself I just tried to stay out of people’s way.  I was still pretty unfamiliar with my plane so it was nerve-wracking.  Luckily I did a good job landing with all those people watching .

Today, I went back to the field with my Kadet, and a new plane that I got at the BCRCC auction for $20 in November.  It’s a “Funtana Mini” made by E-flite that has since been discontinued.  Since the auction, I’ve been slowly getting the parts I needed to complete it, including a receiver and servos.  I reused the motor from another plane that is no longer with us.

My new sport plane

I piloted it on its maiden flight today.  It is extremely twitchy, even on low rates.  Also, something I didn’t expect was how hard it would be to land it.  It requires a fairly high airspeed to maintain altitude, and there isn’t much frontal area to slow it down, so the landing was fast.  I wasn’t able to stop it by the end of the runway so it spent some time in the mud.  Nothing was damaged, but the mud at the airstrip is very stinky.  The second flight was more fun, I actually did some aerobatics.  I still had trouble bringing it down, though.

I wasn’t satisfied with the prop I was using in the first flight test, which was an 11×7 APC E-series.  I bought 2 more, one with higher pitch speed (for the uninitiated, “pitch speed” is the number of inches a propeller would travel forward in one revolution in an ideal fluid) and the same thrust (which how hard it “pulls”), which I think is an 11×8.5 E-series, and one with the same pitch speed and more thrust; a 12×7 E-series, I think.  I tried the one with more pitch speed first, and I’m not rushing to try the other one.  I’m quite happy with the performance as it is.  At full-throttle I can climb-out at 45°, and at 1/4 throttle I can maintain altitude and speed.  I’m also very happy with the observed endurance.  I ran the stop-watch on my radio during the second flight of the day while doing non-stop touch-and-go’s, and after 12 minutes of flying called it quits.  The resting battery voltage on my 3S 2100 mAh LiPo was 11.4 volts.  This roughly corresponds to 20% of the pack power remaining.  With this knowledge in hand I know that I can set the count-down timer on my radio to 12 minutes and not stress-out my batteries too much.

Altogether, it was a good (long) weekend of flying!

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PCB ready for module

This is the starting point.  I cleaned the surface with isopropyl alcohol (IPA).

Solder paste applied

I applied the solder paste as normal, and cleaned the module with IPA as well.

Module seated, waiting for heating

This is just before heating the pads with a soldering iron.  I heated each one until the solder melted, but it didn’t bond with the module.  Before I got too far, I removed the module and examined the results.

Results of the first attempt

I cleaned all the surfaces with solder wick and IPA, and tried again.

Results of attempt two

This time, I held the soldering iron on each pad for much longer.  The solder bonded to the module and the PCB, and it held tight.  However, I took a multimeter to it, checking for continuity.  Nearly every pad was shorted with it’s neighbor.  This sucks.

Another view of try two

With the module throughly bonded with the PCB, and no way to remove it and try again, I decided to try the hail-mary.  I figured that at this point, unless I could think of something, the whole thing was ruined.  With that in mind, I decided to try to reflow the whole thing.  I really had no idea if it was going to screw everything up, especially the FTDI chip on the bottom of the board.

During reflow

The reflow went well, I’m pleased with the look of everything.  I also confirmed that the pins are electrically isolated.  Also, on first glance, everything seems to work.  The microcontroller and USB-to-serial chip still work.  I really just need to verify that the transceiver module works, and it will be a complete success.

The moral of the story is:  Don’t attempt to hand-solder the Micrel module.  It probably won’t work.  On the other hand, if you do get it to work, drop me a line, I’d like to know how.

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My friend Tom agreed to be my test pilot for the first (well, second ) flight. He got it all trimmed and ready to fly. I say it was the second flight because while I was taxiing it around, I decided “what the hell” and decided to fly it… Well it didn’t end that well.

Takeoff cartwheel

Looking on the bright side, the result is a testament to quality of my construction (read: luck).  The only damage was a little dirt on the wingtip.  Not too bad.

Cartwheel "damage"

After that bit of excitement, I decided it would be best to let my test pilot try again  This time, the plane flew quite well.

First (controlled) flight!

Above is one of the first moments of controlled flight for my humble plane.  I have to say, it was very exciting!

I don’t have a lot to say about the rest of the photos, Tom took most of them while I was flying (including the lovely cartwheel photos).  Enjoy them!

Really cool reflections and refractions

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With those goals in mind I decided to select a “trainer,” which is a very stable plane intended for teaching new pilots.  There are several advantages to a trainer in this context.  In a way, I’m training an autopilot to fly, so it’s a fitting.  In addition, a typical trainer has a simple, boxy fuselage.  I think that the simplified geometry should be easier to build around.  The individual plane I settled on is the SIG Kadet LT-25, and my mom was nice enough to get it for my for christmas a few years ago.

Official photo of the Kadet

I wanted the plane to be on the small side because I’m 100% electric for all my planes and helicopters.  I don’t have any investment in nitromethane power, and I don’t want any.  It’s stinky, loud, dirty and annoying.  At the same time, electric power is getting better and better.  The batteries are increasingly amazing in their capacity and power.  Unfortunately, I don’t have any early building photos.  But, I’ll talk about some of the photos I do have:

Wing servo mount

This is the only photo I have of the wing being built.  It went together really well, the laser-cut parts are amazing.  I’m not all that great at making the wing halves meet up right, but lots of epoxy and filler remedied the problem (hopefully).  In this picture I haven’t added the fiberglass reinforcement around the seam.  Finally, notice that the servo hole is a strange shape.  I added a brace in the middle of the opening because 2 micro servos are slightly more narrow than one full-sized  servo.  Using 2 servos allows me to make the ailerons behave as flaps as well as ailerons.  This way, I can adjust the lift of the wings to compensate for the additional weight of payload packages.

Tail mounted servos

As I mentioned, I wanted to make it as easy as possible to add payload modules to the aircraft.  To make this easier, I moved the servos for tail feathers surfaces to the tail itself.  This has 2 advantages, I don’t have to waste space in the radio bay, and it should offset the weight of the comically giant motor I bought.  There is some additional parasitic drag, but I hope it isn’t too much.

Brushless motor

Speaking of the beast, this is the comically huge motor.  It’s a scorpion, which claims to be better than the others because the magnets are rated to 200 degrees celsius while also having the strongest magnetic field (which is apparently rare).  It’s rated to 80 Amps and 1200 Watts continuously.  That is WAAY more than what I need for this model.  I’m not sure what I was thinking when I bought it, but it is what it is.  I spent some time on the motor calculator to figure out a prop/battery combination that seems appropriate to the weight of the model.  Most people have theirs coming in at a finished weight of 4 pounds, so I assumed 5 pounds as a starting point and went from there.

A common rule-of-thumb for electric flight is that for “reasonable” sport flying 40 to 50 Watts/Pound are necessary for brushed motors and 35 to 45 for brushless motors.  In the performance results notice that the current (24 Amps) for a 3-Cell LiPo (11.1 Volts) ends up with about 266 Watts and 53 Watts/Lb, which is just about right.  My speed controller is rated for a 4-Cell LiPo, which would enable about 400 Watts of power.  I doubt I’ll need that much, but I guess it’s nice to have the option.

Spinner binding

Several companies, such as APC, developed special props for electric motors.  They are much more efficient than the older models.  There is renewed interest in propeller design, even in the general aviation circles.  One of the leaders of the movement is Paul Lipps.  He has an interesting article on EAA’s (experimental aircraft association) Experimenter magazine.  Some qualities of his designs are also present on this propeller.  As demonstrated in the photo above, the angle of attack at the root of the propeller is much greater than other model props.  This caused a problem for the spinner I planned on using.  I had to carve the opening larger to accommodate the prop and give some room for comfort.

Power system installed

I skip ahead here a little, but here is a photo of the motor and speed control installed in the fuselage.  At this point, the motor is just sitting there but it doesn’t look any different bolted in.  I later moved the speed control slightly.  In the photo it’s sitting above a balsa panel, I was able to move it underneath.  This left plenty of room on top of the panel for the battery pack.

Top of the GPS tray

I wanted to build a place for the GPS and autopilot circuitboards.  I knew that I could install them in the radio compartment, but it would have been covered by the wing.  This photo is looking through a lightening hole on the top of the fuselage, just behind the wing.  I found some plastic ‘U’ channel and thought it would allow me to slide electronics trays into this bay.  It’s necessary because once the covering film is installed, I won’t have access to the bay from this angle.

Front view of the GPS tray

Here is another view of the GPS tray.  I had to take this picture from the firewall to get the right angle.  You can see the bracing I made underneath and alongside the plastic channels to add rigidity.  On the bottom of the fuselage, you can see 2 balsa sticks.  Those are the mount for the tailwheel steering servo.

Tailwheel steering servo mount

Here, the tailwheel steering servo is mounted.  I decided that I could sacrifice this amount of space in the bay.  I didn’t want the servo to be mounted upside-down on the bottom of the plane because it’s rainy in Oregon, and I didn’t want water to splash up from the main gear onto the servo.  I also thought that if I had a landing onto tall grass there was an increased risk of damaging the servo because there would be more places for things to get caught.  The funny-looking bulge on the right is there so I can remove and install the servo.  The sticks are just wide enough to fit the body of the servo, but there is a wire coming out that makes it hard to mount otherwise.  You can see that the control wires rub against the side of the former.  I later carved them a little to allow for clearance.

Partially covered

As things move along, here is a photo of the plane partially covered.  The entire fuselage is covered, and the top of the wing is, too.  You can’t really see, but the tail surfaces are covered and installed.  I haven’t bought the wheels at this point, either.

Perfectly balanced

Now, things are just about finished.  I installed an eye-bolt in the top of the wing at the Center of Gravity (CG) to check the plane for lateral and longitudinal balance.  Notice that there is a metal tube sticking out of the leading-edge of the right wing.  I decided to install a pitot tube for use later.  It’s made out of aluminum and goes into a silicone tube down the length of the wing to another aluminum tube that exits out the bottom of the wing.  I used Bernoulli’s formula for determining air speed using a pitot tube and determined that I need to get a 1500 Pa (1.5 kPa) differential pressure sensor, assuming 50M/sec as a maximum speed (which is about 100Mph).

Bernoullis formula, Pa versus M/sec

Anyway, back to the plane, I’ve finished covering it. I added a yellow stripe along the whole bottom of the left wing that wraps around the front of the right.  This is a high-contrast indicator of the orientation of the plane.  These aid in the pilot’s ability to determine the orientation of the plane.

Silhouette disorientation example

The idea is to make the 2 possible orientations of the plane look very different through the use of color.  In this example, my plane would be different because the image on the bottom-left would have a stripe along the length of the wing and on the one in the bottom-right image, there would be a single diagonal stripe on the right wing

Top of the plane, fully covered

Bottom of the plane, fully covered

Well, long story-short, I’m done building the airframe.  I need to work on the electronics now.  Luckily (I’m trying to be up-beat about this) the weather is absolute shit, so I’ll have plenty of time to work on it.  Hopefully there will be a break that I can use to take it on it’s maiden flight.

All dressed up with nowhere to go.

There it is all finished.  Note that the deck isn’t wet because I sprayed it off.  We’re supposed to have “torrential” rain this weekend.

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Anyway, when I get one this apparently will work for me.  To even see what’s on here, you need wave sandbox access.

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Seriously.

Well, that’s my plea.  If you have an invitation and are feeling generous leave me a comment.

Thanks!

w00t! A coworker gave me an invite!  It’s pretty fun, but I have no invitations of my own so it’s a little lonely.

Update: I finally have my own invites to give out, I’ll accept 5 requests for invites.  Leave a comment with an email address.  I’ll not actually “approve” the comment so you’re email won’t be picked up by spammers.

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WWDC Lobby Panoramic

I’ll be posting about my trip on Loopt, so if you’re my friend it’s easy… Also, I’ll be filing-out my flickr feed using the “WWDC09″ tag. If something good is announced, I’m likely to gush about it here. However, if the rumors prove true, and there isn’t something else pretty great, that’s not likely to happen. :/

Media out in full force!

Keynote line

Yep, I'm that close...

They've got pomp and circumstance down...

Breaking news: Forestall leaves Apple, becomes Scientist.

Forestall the scientist

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- Update: In the 2 days since, there has been an additional 1000 users!

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Hardware

This was probably one of my most time consuming projects.  Hopefully I can do some justice to the time and work spent through this post.  I should probably begin by describing the whole system.  First, the TV is lifted up & down by a “Lift Tech” lift.  By the way, they get the prize for the most original company name ever.  Their controller box has a port that allows home automation systems to control its operation.  They did a really good job of making it extensible.  You can control it in a variety of ways: short one pair for going up, another for going down; short a pair for down, open for up; etc.  I had intended to use the first mode, but I think I fried a channel on my opto-isolator.  I ended up using the second method because it only required one channel.  Unfortunately that means I can only have the TV up, or down.  I wasn’t too disappointed, though, because I don’t expect to want it any other way very often .

TV Lift controller box

The board I designed to interface the TV Lift to the server was fun to design and build, even though it was prone to error.  I had originally intended to use the Microchip ENC28J60 ethernet controller. I thought it’d be cool to have the iPhone app connect directly to the board’s ethernet controller and microcontroller. Unfortunately, I screwed up the interface from the ethernet controller (specifically the physical layer circuitry) and the magnetics. This interface is harder than it looks, trust me. I thankfully included a serial port on the board (which I had other plans for) and used that instead. This choice made the microcontroller software extremely simple. All it really has to do is wait for a ‘d’ character over the serial port and lower the TV, a ‘u’ character lifts the TV, and a ‘s’ character queries the controller for the current state. I’ve included an image of the schematic for the board, in case you are curious about my lofty intentions.

TV Lift Schematic

If you’re interested, the board I used on my reflow soldering toaster oven page is the TV Lift board.  Incase you don’t want to go over there, here is a picture of it mostly finished up:

Controller board installed

Using the RTS line for reset

There is one more thing that I had to change.  For some reason the controller board that I made crashes after a while.  I have to use a ladder to reboot it (power-cycle).  Hauling the ladder around is annoying, and I don’t like doing it.  To allow myself to reboot it remotely, I added a diode from the MCLR line (reboot) of the microcontroller to the RTS line of the serial port.  The RTS line is used for modems from back in the day.  Now I can use it to force MCLR low, to reboot the controller, if it’s “low” (-5 volts).  It’s a hack, but what are you going to do?

Software

The software for this project is deceptively simple.  The iPhone software basically connects to the server using a socket, and if the “up” button is pressed it sends a ‘u’ over the socket, and a ‘d’ if the down button is pressed.  That’s it!  Server software is almost identical, however it listens to the return of the serial port and expects my controller board to return a ‘U’ or a ‘D’ from the ‘u’ and ‘d’ command.  If these are not received, the board is reset and the command is tried again.

Conslusion

Well, that’s all there is.  I hope you’ve enjoyed it, I know I have.  Please, feel free to ask any questions in the comments section!

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Look! You can see my house mid-construction!

View Larger Map

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The WMR 918 has a serial port that sends-out all the data that it collects (and lightly processes).  I have this signal going into my home server, which is running the open source wview.  Because my weather setup is a bit different than what is typical, I had to make some changes to the source code.  (probably the best part about open source!)  I guess most weather stations come with a “mushroom” sensor which is a thermohygrometer (temperature and humidity) that is encased in a radiation shield (so direct sunlight doesn’t affect the readings).  I don’t have one of those.  My outdoor temperature sensor is reported differently on the serial output.  The wview software was expecting a certain kind of data packet, and having never gotten it, it never initialized.  Once I changed the source code so that it ignored the difference I was all set. B.T.W: The thread about this process is on the wview google groups page.

I’ve gotten the data up in several personal weather aggregation services. I’ve decided that I don’t really like weather underground (way too cluttered), but I’m up on PWS (Personal Weather Stations), and APRS (Automatic Position Reporting System). APRS is a weird amateur radio thing. Basically, what it was designed to be is a way for small bits of digital data to be passed around so that, especially during search-and-rescue, operators can know where one another are. Over the years it has been expanded to include many interesting uses. One of which is the sharing of personal weather station observations. Eventually, NOAA even started using the data in their models. One of the many things I want to do, one of these days, is install a APRS node in my car. I know it is geeky to the max, but that is what I am.

Anyway, back to the point, everything works!  I hope you enjoy the fascinating (not really) weather trends from Philomath Oregon!  Oh, and hopefully soon I’ll have a handy widget that displays a digest of the current conditions in this sidebar.  But for now, feel free to check the current conditions page.

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Amity Vineyard Panoramic - click the image for a full-size version...

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Reflow Oven temperature profile

I’ve decided to spend some time profiling the toaster oven.  In addition, I’ve made a simple controller board that may get the brains to manage a reflow operation on it’s own one day.  For now, I’m satisfied learning more about the oven’s capabilities.  An interesting thing to notice is that it (appears) incapable of satisfying the recommended profile from Kester.

I wanted to start with a very simple controller that gets most of it’s brains from an attached computer.  This is a somewhat central tennant of the way I build most projects.  The reason for this is that computers have really huge screens, and nice keyboards so it’s easy and cheap to have a cool UI.  For this project I’m still working on the OpenGL for the realtime graphing of the temperature profile, but you can see what I have designed so far:

Oven Controller UI

The left side of the window is where the realtime graph window goes, the oven system status is in the upper right, with the reflow profile defined by the user in the bottom right.  Anyway, back to the controller hardware.

The controller is built around a PIC microcontroller and the MAXIM 6675.   The 6675 is a thermocouple conversion chip that handles all the analog complication of dealing with thermocouples (including cold-junction temperature).  The microcontroller interfaces with it through a simple synchronous serial protocol.  One thing that you have to keep in mind with this chip is that if you request a sample more than 4 times a second then it doesn’t finish the conversion.  I decided to let the microcontroller handle waiting for the appropriate amount of time, taking a sample, and sending the data over the serial port.

Because computers don’t have serial ports anymore, I have to include serial to USB converters on everything.  In this case I used the FT232RL schematic block that I copy and paste whenever I need it.  Here is an image of the completed schematic (Full size PDF):

Reflow Oven Controller Schematic

Like almost all my projects, I got a board made at BatchPCB.  It turned out great:

Oven Controller Board

Unfortunately, I wasn’t able to find a nice socket for the somewhat standard plug they put on the end of thermocouples.  In this case, I just used a screw terminal.  The posts on the left go to the thermocouple wires.  I’ve included another pair for adding a relay that could be used to switch power to the oven.  Also, I’ve included a port that could control a R/C servo that could open the front door to facilitate rapid cooling of the oven.  Eventually, I’d like to allow this controller to begin a reflow cycle when the button in front is pressed, runs until the target temperature is reached, shuts off power, and opens the door at the perfect time.  For now, I still have to watch and stop when I feel it’s right.

The thermocouple is installed just by using the friction of threading it through the oven rack that is installed above the board.

Oven thermocouple installation

To keep everything relatively tidy, I double-stick taped my controller to the side of the oven:

Oven Controller Installation

Finally, I’ll analyze the graph from the beginning of the post.  For you’re convenience, here it is again:

Reflow Oven temperature profile

The blue graph is the recorded profile used while soldering an actual board based on my observations.  I stopped the oven cycle based on the advice I gave in my other post about the Toaster Oven Reflow Soldering post.  For the Green trace I ran the oven until the thermocouple read 210°C.  I decided to run it without a board in it because I didn’t want to smell burning FR-4 .  I’m not saying that it would have actually burned it, but I realize now that I really need to calibrate my thermocouple against a trusted reference thermometer.

To compare the actual results against the specifications in the Kester datasheet, I’ve included a line for the maximum and minimum profiles.  For the preheat phase of the profile all that is required is that the temperature increases less than 2.5°C/second, up to 150°C so I didn’t include it.  Once it reaches 150°C the temperature needs to increase between .5 and .6°C/second up to 180°C.  From 180°C to 210°C temperature needs to increase at a rate between 1.3 to 1.6°C/second.  As you can see the toaster oven almost keeps track with the 150-180° rate, but can’t achieve the 1.3-1.6°C/second ramp rate.  I’m not sure what the exact effect of this is, but I’ve had good results so far.

Anyway, it was an interesting exploration.  I do kinda wish I was able to match the correct profile, but I’m glad in a way that it doesn’t because I don’t have to implement a PID temperatue controller .

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I added a serial port to my wireless router so it could monitor the weather.  I know, why does a router care what the weather is like?  Well, it doesn’t, but I do.  Actually, I want to add a weather widget to this blog and also upload it to weather underground (not the one with Bill Ayers ).  << Correction! I’ve finished the weather station, and I’m not using the netgear router or weather underground.  See this post for details. >> I haven’t finished any of that yet, but it came in handy later when I bricked it!

When they designed this AP, Netgear was nice enough to make it easy to open.  All that you need to do is pull back the rubber feet and use a T-9 screwdriver.  The little feet even stay captive during the process, mighty convenient.

Removing the screws

The bottom plate comes right off, revealing the mainboard, which lifts out.

Disassembled

Unfortunately, I don’t have a device without headers installed, but you can see them installed in the lower left corner.  The single-row one is the serial port, the double-row is the JTAG.  From the factory mine had solder blobs on the serial port.  I had to use solder wick to remove it.  Once the holes are cleaned out, installing the header is a snap.

Now that it’s easy to attach to the port, we need to convert the 3.3v CMOS serial signal to true RS232.  The typical way you do this is to use a RS232 transceiver.  I had a SIPEX transceiver lying around, so I used that.  Just follow the datasheet for whatever you use.  The pinout for the serial port on the netgear is:

1 -- VCC
2 -- RXD
5 -- TXD
6 -- GND

I’ve attached the approximate schematic that I used.  There are a couple of important things to note, because the router uses 3.3v and the RS232 transceiver uses 5v we need to negotiate the difference.  Referencing the transceiver’s datasheet, the minimum voltage necessary for a ’1′ is low enough that a 3.3v CMOS signal is sufficient, so we can just hook it up.  The signal going toward the router, however should not exceed it’s VCC.  To achieve this using a minimum of parts we use a pull-up resistor fed from the device’s VCC and a diode biased toward the transceiver.  This way, when the transceiver is outputting a ’1′ the 5v are blocked, but while outputting a ’0′ it will drop the voltage sufficiently enough for the router to see it as a logical low.

schematic

Top view of the adapter

Bottom view

If you want the router to be the “slave” of the serial connection (like a modem) then reverse the TXD/RXD pins on the DB9 connector (pins 2 &3).  I specifically wanted the router to be the master to hook it up to other stuff (my weather station, remember).

To get the 5V necessary for the transceiver I tapped the 12V power from the wall adapter and fed it through a 7805.

Stealing 12V from the wall adapter

Adapter installed on mainboard

Adapter board installed

Mainboard and adapter in case

Connected with a NULL Modem cable

In the above photo I’m using a NULL Modem cable because, remember, the router serial port was installed as if it’s a computer.

Netgear preboot console

It works!  The photo above is the preboot console of the router.  Notice that the MAC address is FF:FF:FF:FF:FF:FF.  I’m not just paranoid, this is one of the failure modes of these routers.  The DD-WRT firmware overwrites some of the NVRAM in a weird way and this happens.  It’s pretty screwed, but at least with a serial port you can fix it

Anyway, enjoy!

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System Schematic

Schematic of Time-lapse capture system

I used SecuritySpy by BTV to capture the frames.  This software was intended for businesses interested in “Loss prevention,” otherwise known as catching shoplifters.  For that reason, it’s a little spendy and the features aren’t perfect, but it does work rather well, and it’s reliable.  There are 2 primary features I was looking for: Storing a time-lapse video, and providing web access to the camera.  Security Spy does provide these functions, and it let me set a schedule for beginning and stopping the recording for each day on a weekly schedule.  Also, you can modify the settings over the web interface.  I had some trouble with SecuritySpy crashing, and by contacting support they provided me with an AppleScript that monitored the application and restarted it.

The problem with daily recordings, however, is that they need to be combined.  About once a week, I would download the videos for that week and remove the times the crew wasn’t there, and combine them in iMovie.  Now that the project is over I could never imagine the pain doing all that work in would sitting would cause.

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Soldering Surface Mount Devices (SMD) can be challenging work, especially with the no-lead (legs, not pb) parts that are so popular with device manufactures these days.  A useful and surprisingly easy solution is “Reflow” soldering.  Reflow is when you use a paste of solder to hold down parts while the board is heated in an oven.  During heating, the solder melts and surface tension makes the parts align themselves in a much more uniform way than is possible with an iron. I’ve got more information about the toaster here, including a controller I made for it.

Board used in this example.

Preparing for reflow is a simple process.  The most important part, as usual, is having a good foundation.  In this case that means a good circuit board.  I have made my own boards in the past, but BatchPCB is just so damn convenient.  They create 2-layer boards with soldermask and slikscreen for $2.50/inch.  The turn around time is pretty long, ranging from 3 weeks to as long as 6 weeks.  Here is an image of the board I’m using for this example, and one I got from BatchPCB.

While it’s not completely necessary to have a soldermask, I find that it really helps keep the molten solder where it is supposed to be.  If you make your own board, make sure you get a complete etch and that there are no specks of copper around pads.  They could prevent the solder from staying where it belongs.

Laying out the parts

I’ve just started to lay out all the surface parts before I begin a large project.  It’s kinda nice, all the stress of finding the parts is isolated to a time where you aren’t in a hurry.  I printed out the sheet twice as large so there would be plenty of room for the paper tape that carries passives.

Solder paste syringe from kester

Once everything is laid out, ready to go, It’s time to break-out the solderpaste.  I keep my solderpaste in the fridge, but I’ve heard of some people that just leave it lying around, and have for months, and say that it’s just fine.  I like applying it cold, because it’s a bit more viscous; though that means you have to press a little harder on the plunger.

Solder paste applied to board

Placing the paste on the board is probably the most delicate step.  If you put too much on some problems can arise.  While the board gets warmer the paste spreads out (like a cookie baking) and if there are several components close together the blobs might join.  If this happens the surface tension may drag them together as the solder melts.  This has only happened to me once, though.  Another reason to avoid too much solder is that you’ll create solder bridges on IC parts with close leads.  To be fair, these are nearly unavoidable.  Finally, if you add too much the extra may squeeze out in a really strange way.  If you put too little on you’ll need to add more solder with an iron.  There is clearly a balance, but I’d err on the conservative side.  The amount I put on in this picture was about right. Basically, it should look a bit like a hershey’s kiss.  For ICs just put a bead along the leads.  Put on a little as possible while covering all the pads evenly. I had to remove some with solder wick from the IC’s but not very much.

Placing the components on the board

Putting everything the board is easier than with standard soldering.  You don’t need to make sure that things are lined up very accurately.  However, for the reason outlined above, it is important to make sure that the solder paste doesn’t touch between the small components.

I place the boards in a cold oven, and bake at 450°F for about 8 minutes.  You should watch to see the solder melt.  Don’t worry about thermometers, or controllers, really.  Trust your eyes.  If the solder melts you know that you have achieved the proper temperature.  Leave it in there for about another 30 seconds with the heat on to make sure that you’ve at least reached the critical temperature everywhere (while hopefully not exceeding it much).  Turn the heat off and leave it in for about another 20 seconds.  Open the door and wait for about 5 minutes and remove the part.  That’s all there is!  Good luck!

All done!

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To try to fix them, I re-routed the servo wires to the port side of the vehicle and moved the motor leads to the starboard. I also looped the servo wires through a ferrite bead. I also tried to fit the motor leads through one too, but I don’t have any big enough. Here is an image of result:

Original configuration

Here is what it looks like when I was finished:

The result

Ultimately, I’m a little disappointed with the result.  It still twitches some, and I ended up crashing it breaking a blade grip.  I don’t think I’m going to fix it until I can afford a Spektrum DX6 or DX7.

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Finished product

With many devices these days, power comes in the form of DC 5 or 12 Volts.  It seems that battery chargers are especially bad because they require upwards of 10 Amps and don’t include a wall-adapter.  Probably one of the best solutions to this problem comes in the form of a standard computer power supply (ATX).  These devices have several nice qualities and only a couple caveats. They are capable of providing plenty of current: 10-15A 12V, 10A 5V, etc. are small in size, and generally efficient.  However, they also require a couple of considerations: cooling needs, voltage levels (12V is really more like 11.5V), and Switching Noise.  Switching Noise comes from the way they are designed to be small, efficient, and cost-effective.  Switching-Mode Power Supplies generate a given voltage by turning on-and-off a higher-voltage source so that the average of the output is the desired voltage.  This is then filtered to smooth the result enough such that it is appropriate for the application.  Computers don’t require voltage sources that are that clean, they are almost always run at 3.3V and lower.  They generate these voltages in a different way.  Anyway, enough justification for the choices made, on with it:

First, though: Do not follow these instructions!  I have no idea what I’m talking about.  If you follow these instructions, you’ll die, you pets will talk and the world will cease to be.  I take no responsibility for the idiotic things you do.

Step 1: Disassemble the power supply:

Be careful for latent energy in the capacitors!

First, you want to find the screws that hold this thing together.  They are often in a bit of a strange place, on this model they are on the top, far away from where the case separates.  Notice that the sides are held in by the lip punched into the steel.  Also, you may need to cut-off the ends of the long wires at this point (the connectors that attach to your motherboard, CD-ROM disk drives, etc) as they will no longer be needed.

There are a couple things to pay attention to about your power supply.  You’ll want to check to see if the main power connection and the fan have removable connectors on the main circuit board.  If they do, you’re in good shape.  If not, it’s still possible to continue, but it’ll be a little more challenging.  You’ll have to carefully solder them once everything is installed in the box.

The next step is to remove the “IEC” socket and switches (On/Off and 110/220) from the case.  You may have to do more or less than I had to, depending on the specifics of your salvaged power supply.  I had to desolder the wires from the IEC socket to the On/Off switch, and the wires from the switch to the harness that connected to the mainboard.  The 110/220 switch was mounted fully on the inside of the case and was left alone.

What was required on my box.

Now, we need to prepare everything for mounting in the new wooden box.  Because these power supplies are produced in mass quantities, the manufacturers do whatever they can to save money.  This usually includes using single-layer PCBs.  What that means it they have to move the ground plane off the PCB.  This means that the metal case is the ground plane.  So, we have to keep it.  In this case, I measured exactly how little case I could get away with and broke out the dremel.  Here is all the parts you need from the case (not including the main board):

All you need from the case

Step 2: Preparing the box

Now, we need to find a wooden box to encase the power supply.  I found mine from the local craft store.  In the next image you can see that I’ve cut holes for ventilation, the switch and IEC socket.  We also need to re-solder the wires from the socket to the switch.  Make sure that the HOT wire (black) goes through the switch.

Ventilation, switch, and wall power

Power wires soldered back on

Glue the mounting plate into the box.  Make sure that the plate won’t chafe the wires leading to a short, and that the wires can reach.  I used super glue (CA) to glue the plate to the box.  I was happy to note that it bonded to the metal pretty well.

Mounting plate glued down

Step 3: Installing the Power Supply

Screw the power supply mainboard onto its mounting plate.  Make sure you mechanically and electrically attach the ground wire to the plate.  During this step, it is imperative that you make sure the ground wire doesn’t short anything out.  Now is also the time to attach the wires to the mainboard.

Wiring the power input to the mainboard

I glued the 110/220 voltage switch to the side of the inside of the box, using CA again.

Now, we strip and gather the 12V wires (yellow, usually) and an equal number of ground wires (black) and attach either spade lugs or something else convenient.

Get your hands on some banana plugs to use.  They’re available at RadioShack, but they suck, so try to get them somewhere else.  Drill some holes on the front and mount them.

Mounting of the 12V wires

In order for the power supply to work, the “PS_ON” wire must be tied to ground.  This is usually the green wire, but you should probably check for yourself.  Also, now would be a good time to “Smoke test” your installation.  Sometimes, switching power supplies need to have a non-inductive load to turn on, such as a light bulb or something.

Step 4: Finishing up

Airflow Baffle

These switching power supplies are really efficient, but often need some active cooling.  I decided to make a baffle plate to mount the fan in it.  I traced around the fan and cut it out, and center punched the screw holes.  I think it fit nicely.  The writing on the lid is the voltage and amperage rating copied off the original case.

Below, I’ve included a a photo of the whole device.  Everything seems to fit really well.

All done (only 12v included)

See, it works!

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IR Transceiver built using home made PCB

For use with my home theater PC I developed an IR Transceiver by combining 2 projects (Receiver, Blaster).  Note that this device may be taxing of your serial port, I take no responsibility for any damage you cause to your equipment.  That said, I’ve provided PDF’s of the silkscreen, copper layout, and the Eagle PCB files.  But first, the parts list:

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