Friday, February 24, 2012

Tutorial on Using the Jointer / Planer

We're rounding in on the end of my woodworking series for this winter.  For this last major tool (except the lathes, which are a whole other series of their own), I'm going to talk about the Jointer / Planer.

Video:


The Jointer / Planer is a combination tool, the jointer on the left, and the planer on the right.  The jointer/planer is primarily used to make boards straight.  When you buy wood from a lumber yard, it is still very wet, and as it dries it will inevitably warp in one or more dimensions.  Of course, these warps aren't generally appreciated in fine cabinetry (unless you're using it to make a bold statement or something).  Traditionally, this warp and bow of a board was corrected by using hand planes (which I have several of), but I was a little compressed for time this break, so why break a sweat when you can throw 120VAC at the problem?
Given a board that is arbitrarily shaped, you first need to form a single straight side, which you'll use as the reference for every other side.  This is done on the jointer, which is the long platform on the left of the picture at top (that my elbow is leaning on).  It consists of the in-feed table in the foreground, and the out-feed table beyond the blades (which are under the bright red guard).  Both feed tables were machined to be very flat, and the in-feed table has a screw thread underneath allowing you to offset it below the plane of the blades and out-feed table by anything between almost zero and almost an eight of an inch.  I tend not to use the jointer adjustment much; I have it set at 1/32" and will just keep taking passes on it until the board's flatness meets my requirements.  After feeding a board through the jointer, its flatness can be checked with a good quality, and very long, level.

Once the first face is flat, you can turn the board 90 degrees and use the first side as a reference to get one of the sides flat and square to the first (so the board doesn't end up as a parallelogram).  Once you have this second side flat and square, you would eventually rip the final width of the board on the table saw, since the jointer has no control on the final geometry of the board; it just makes a side flat.  This is shown as step four in the diagram above.

To get the second wide face flat and parallel to the first, you would run it through the planer.  The planer has an adjustable bed, which you can raise or lower to meet the requirements of your board.  On the in-feed side, it also has a veneer gauge showing how many 32nds of an inch you will be taking off on the pass.  Unlike the jointer, once you run a board through the planer, if you were to run it through again, it would remove almost no material, so you will need to continually raise the bed until the board is flat and meets your final thickness requirement.  As shown in the diagram above, this third step is what you use to define the thickness of the board, should it need to be the same as another board, fit in a dado, etc.

In addition to being useful for flattening wide boards, I've used the planer as an easy way to reduce 4"x4" fence posts while keeping them square, by feeding it through, then turning it 90 degrees and feeding it through again.  This is how I was able to make the 3"x3" stock for my Kubb set all from a single fence post.

Monday, February 20, 2012

Cutting with a Tablesaw

Another video on woodworking, this time with the big boy of the shop, the tablesaw.  I posted all the previous articles in this series back in December, if this seems to be coming from left base here.

Video:


To try and avoid the 15 minute long talk about cutting utensils like I did on the drill press video, I'll talk about your various options as far as blades not in the video.

Your first saw blade that you will get free with your table saw is typically a "combination" blade.  If you take a close look at the blades on a combination saw you'll notice that it has widely-spaced teeth with a slight angle in alternating directions.
This is because the combination blade is designed for both cross and rip cutting.  Cross cutting is when you cut perpendicular to the grain, and rip cutting is when you cut parallel to the grain of the wood.  For cross-cut, it's important to have the alternating angled teeth to help sever the grain cleanly, since the wood grain is fibrous and tends to tear the wood when you try to cut it.  For rip cutting, it's important to instead have the wide teeth spacing to have a chiseling action as the blade scoops out material.  The combination saw is designed for both of these actions.
 The combination blade is designed for both rip and cross cuts, but as you'll notice that our 20-year-old combination blade is still in pristine condition, it does neither well.  The combination blade is a compromise between rip blades and cross cut blades.

This is what a good rip saw looks like.  You'll notice that this one actually has seen some action in our shop.  The primary cutting action is performed by the front blade in the set, which is square.  You'll notice that the second through fourth blades of each cluster are angled, just like you saw in the combination and will see in the cross cut saws; these still help getting a clean cut, even though you're making a rip cut.

You'll also notice that this blade has carbide tips, which are the rectangles tipping each tooth.  The cost difference between a carbide blade and a simple steel blade is significant, but if you're doing fine woodworking, carbide is a difference worth its price. On the other hand, if you're using your tablesaw to hack up the old cherry tree from the backyard for firewood, for all that is mighty, please make sure you're not using a carbide blade.

On the opposite side of combination blades from rip is the cross-cut saw.  This blade is specifically designed for cutting perpendicular to the grain, which is more the domain of the radial arm saw than the table saw, but if you get 10 inch equipment for both, you can use it on either.  The cross-cut saw can be recognized by the fine-spaced teeth angled in alternating directions, which do a very good job of severing the grains as the wood crosses the radius of the saw, but aren't as good at removing the bulk material you need for rip cutting.  Again, the pictured blade is carbide-tipped, which is an easy way to spot a much nicer saw blade.  These two carbide saw blades have lasted us decades, so it's hard for me to say that the investment wasn't worth it.

The careful reader will then ask about plywood.  Plywood is the very common and cheap building material that, if you stop and really look at it, is actually several very thin layers of wood glued together, with their grains at right angles.  This is great because it means plywood is more isotropic than traditional wood board (it's more consistent as far as strength in one direction or the other due to the grain), but when you're cutting plywood, do you use a cross-cut blade, or a rip blade?  You'll always be cutting the wood half rip and half cross, so what is a man to do?
I kid you not, there is plywood saws.  As you'll notice, these blades are much smaller than anything we've looked at so far.  You could say the plywood blade is making the opposite compromise that the combination blade makes; instead of coarse angled teeth, it has very fine chisel teeth.  This suites it well for cutting plywood, since plywood doesn't tend to form large chips like ripping or have the fibrous consistency which begets cross-cuts, but instead forms many small chips which need to be scooped away quickly.
You can actually take this argument a step further, to what's called a veneer saw.  Wood veneer is the very thin layers of wood which are glued together to form plywood and the wood grain surface of particle-board desks and shelves.  The veneer saw's teeth are almost exactly the same size as the plywood saw's, but you will notice that the side of the saw has an angled lap to it, which helps to prevent tear-out or chipping when you are trying to cut the extremely thin veneer (usually <1/8 inch).  This lap, unfortunately, only goes in about an inch of the radius of the saw, so using this blade to try and cut thicker material (or even plywood) isn't advised., since the saw gets quite a big thicker above this lapped radius, and you really shouldn't be using such a specialized saw for anything else anyways.
The last saw blade of interest isn't actually a single saw blade, but is what's called a dado set.  Dado sets are a series of blades of different thicknesses which can be combined to form a single cutting face of variable width.  This is used to cut dados and grooves in wood, which are the cuts part-way through material at joints to act as a recess to hold perpendicular boards.  The classic application of a dado is the joints in a bookshelf (before Ikea came in and replaced every wood joint with pegs and dowel nuts) where the shelves insert into the side panels.
The problem is that every dado is going to need to be a slightly different width.  This is where the dado "set" comes to play.  At it's minimum, it has two 1/8" blades, which appear somewhat like a high quality combination blade split onto two discs (this is such that you can also cut grooves with it, which are dados but parallel to the grain).
The second part of the dado set is several S blades, which you can install between the two main blades, to move them apart and to remove the center material of the dado.  You'll notice that these S blades only have two teeth on them, in sharp contrast to every other saw blade which have "hella" teeth.  This is because the middle of the dado isn't a particularly important surface, since it will have little to do with the final fit of the boards, and will be covered by the perpendicular board once assembled, so rough-cutting this inner face is fine.
By sandwiching the S blade between the outer two, you get a variable width blade to cut the exact width dado you need.  Notice that the two external blades have a very definite inside and outside, which is important since the angled teeth need to be attacking the finished surface, not retreating from it.
 My set happens to include a 1/16", two 1/8", and a 1/4" S blade, meaning I can set it up for 1/16" increments from 1/4" to nearly 1" by swapping in whichever blades I'd need to meet my needs.
But the dado set has more; it comes with five precision spacers to allow you to widen the dado in increments less than 1/16".  Using a variable number of these spacers and S blades, you can pretty much cut a snug-fit dado for any thickness of board.
If you're using multiple spacers, you would want to try and spread them between S blades if possible, but even if you gauge out more than the overlap of the carbide tips, you'll only be left with a sliver which you can just snap off (or it will likely break off during the cut) and you can sand it down.

So that's it as far as my collection of saw blades.  Again, please don't think that this video and post are enough to learn how to use a table saw, so make sure to read your owner's manual, and get professional training if available.

Sunday, February 19, 2012

USB IR Toy - Free PCB Build

Dangerous Prototypes never ceases to amaze me with how they are the poster child of open source hardware.  You can literally go back in the forum archives and watch their products evolve as members bounce ideas back and forth.  Then, in the end, they post everything online with an open license, get a batch of 100 put together to sell some, and let people do with it as they will.

As part of this amazing outfit, they give away free PCBs.  I've gotten a few before, and I got one again.  This is their USB IR adapter, to allow you to give any computer infrared transmitting and receiving capability, which is valuable if you want to use your computer to receive commands from IR remotes (we have a computer set up as a DVR at home), or want it to be able to transmit IR commands to any other device which expects them.

Thursday, February 16, 2012

A Basic Introduction to Phase Locked Loops

Phase-locked loops have been an electronics concept I've never quite understood.  Wikipedia of course has a good cursory introduction on the subject, but PLLs are so dynamic that it's hard to really grasp the concept regardless of how many articles you read on it.  Horowitz and Hill of course do a decent job in The Art of Electronics, and the ARRL Hardbook adds some insights on the subject with regards to analog applications, but I still didn't quite get it.  Jeri Ellsworth hosted a video on the subject, but even that didn't quite give me the intuitive understanding I was looking for.
The inevitable next step was to break out the breadboard, put together a simple PLL, and just play with it some to try and really get the concept.  Luckily, the classic 4000 logic series includes the 4046 PLL chip, which includes both a voltage controlled oscillator and both types of phase detectors.  After putting it all together, I figured I'd record a video and let you enjoy the play-by-play as I try and break it all down for you.

Video:


The PLL is an excellent example of your basic control loop.  Fin is the signal being fed into the loop, which needs to be recovered.  This is then compared to the VCO's frequency, and this comparison is used to speed up or slow down the VCO to bring the two frequencies in lock.  Of course, there are all sorts of extensions and alterations that can be made to this loop, so don't think that this is it.
The parts list isn't too bad; just two CD4046s and some basic resistors and capacitors.  The 4046 on the left of the schematic is being used just for its VCO as the input to the right one, which is actually wired up as a PLL.



 FM PLL Demodulation Video:


Of course, it's hard to understand why we're so excited about this phase-locked loop without a solid example, so as a follow-up to the first video, I made some alterations to use this VCO and PLL to use it to transmit frequency modulated audio.
 The needed modification is minor; I changed the VCO frequency controls to have it running at 100kHz instead of the 1000Hz I used for the first video.  Then I set up the VCO so it'll be modulated by an audio signal fed in, and amplified the VCO control voltage on the PLL.

Wednesday, February 15, 2012

Howto Replace Wheelbarrow Wheel with Foam Core Wheel

My parents have been doing quite a bit of work in our yard since the last of us kids moved out; they figured that now that we're all gone off to college, they no longer needed lawn, and have completely converted the backyard into one absolutely huge vegetable garden.
Unfortunately, our aging wheelbarrow just couldn't keep up its half; the tubeless tire just wouldn't hold air anymore.  We finally tired of constantly fighting it trying to air it up, so we decided to switch to the relatively newly available foam-core tires.  Replacing it is quite easy, so our wheelbarrow now has a tire that will never go flat, with the one small disadvantage that you need to be more careful about over-loading the barrow and damaging the foam.  For just moving dirt, it has been fine, but for moving rock or sand or concrete, I would be very cautious.
Most wheelbarrows' axle is little more than a piece of round-stock held in with a couple bolts.  The bearing is in the wheel itself.
The axle had seen better days, so I decided that it needed some tender love and care to take care of that rust.
A simple wire wheel attachment for hand drills can be had that'll do the job.
Simply slide the axle into the new wheel, and reattach the axle to the bottom of the wheelbarrow.
And you're done!  No more worries about firing up the air compressor every time you want to move around some dirt or collect weeds; it'll just always be ready for light action.

Thursday, February 9, 2012

Another Failed WRT54G Upgrade

I can't believe how lucky I must have been the first time.  I've tried upgrading the RAM in these WRT54G routers four times now, and have only managed to get it to work once...

Video:


This is a rather painfully long and boring video where I show you  the general timeline for replacing a pair of TSSOP-II-54 SDRAM chips using ChipQuik and a magnitude of skill and/or luck.  I do go into some interesting asides about electronics in general as I chatter away for 30 minutes, so just think of this as a slightly more focused version of one of Dave's Drive Time Rants.  If you think the format is long and boring, don't bother calling the kettle black.  If you actually did find this interesting, insightful, or just some order of entertaining, feel free to color me surprised in the comments.

The new chips I'm installing in the video are IS42S16160D.

Sunday, February 5, 2012

Sniffing Pager Network Traffic - The Hardware

You remember pagers?  Those hip little devices clipped to people's belts in the 90s which were on the frontier of today's always-plugged-in culture.  Originally they were only smart enough to start beeping when you were needed on the job, but over time more sophisticated pager networks were built allowing for numerical pages, text pages, and eventually binary pages (just in time for email and cell phones to plunge the entire system into almost complete irrelevance).

I never had a pager of my own.  I was born just late enough (1989) that society still remembered how to plan social engagements ahead of time long enough to allow me to live without until cell phones became a viable option for teenagers back in the early-to-mid 2000s.  Meanwhile, I was born early enough that I was very much aware of the wonder of the pager network, was very much fascinated by it, and was endlessly appreciative of the decade head-start that pagers gave public school districts to slowly come to terms with the idea that teenagers possibly have other things to communicate about other than drug dealing.  The only person I knew with a pager was my father for work, and however unfortunate it usually was when his pager went off, it was usually followed the next day by fascinating stories about how one of his file servers blew up or he managed to fix some show-stopping problem on the other side of the world.

Pager systems are, at the core, a fairly simple network.  Telecomms install hugely powerful transmitters through "service regions," which blast out every page at blazing speeds like 1600 or 6400 baud.  Every now and then pagers would raise sticky questions about "reasonable expectation of privacy" with regards to listening to other people's pages, since the pager networks are based on the early 20th century optimism that everyone on an electronics network are inherently nice people, so there is no form of encryption or privacy, other than pagers only displaying their own pages.

I like to think of myself as an inherently nice person, but the temptation of sniffing the pager network to get a tantalizing peek into the lives of people significantly more interesting than myself has always been appealing.  Pager data is usually transmitted using the fairly simple FSK (frequency shift keying) method, where the frequency of a signal is selectively changed either above or below a fixed center to indicate either a one or a zero (or a predefined set of ones and zeros, for more sophisticated systems).

In the ideal world, to protect the honor of my amateur radio license, I would home-brew my own 465MHz FSK receiver to sniff these signals, then it would simply be a matter of reading patents and graduate theses to down-convert the coded signals back into numeric or alphanumeric pages.  Alas, we live in something far from a perfect world, and I have been in a rocky long-term relationship with analog electronics fraught with anguish and despair, so this was a project I never considered too seriously until I could find some sort of reasonable solution to the RF front-end issue.
Imagine my pleasure when I was wandering around the Silicon Valley Electronics Flea Market this summer and stumbled upon Paul Rako with an entire card table full of pagers which he was selling for something trivial like $1 a piece.  He was marketing them as "the hippest timepieces on the block," which seemed to not be nearly as effective as the fact that they have vibrator motors in them, which everyone was actually interested in (he could have probably done a better job if he just sold the toothbrush to go with it).  In any case, I was likely the only person digging through the pile actually looking for a working pager, and with the deliberateness of pure ignorance I very carefully selected a Motorola Advisor II which still had its very hip belt clip and looked to be in reasonably good condition.  One T6H torx screwdriver later, and I had this minimalistic piece of communication technology open.
Initially my optimism was not particularly high; I was expecting the contemporary basic peripherals all leading into one mysterious epoxy blob, so I was pleasantly surprised when I discovered that the pager not only had a separate RF daughterboard, but was kind enough to use discrete components and make no effort to conceal their identities.  A little poking around between the circuit boards and Google and I found that this pager uses the Toshiba TA31142 FM detector specifically designed for pagers.  What luck that the datasheet was even kind enough to indicate which pin the finally demodulated FSK data was outputted on (the red emphasis in the figure above is my own).  This means that with some tricky soldering, I can take advantage of the fact that Motorola put all this effort into building a good FSK quadrature detector, and I can spend my time in the much more interesting and pleasant digital electronics land.
 Tapping pin 15 on the detector gives us a 3V serial signal running at 6400 baud.  Ground is pin 19 on the IC, but I opted to tap the more convenient ground plane circled on the left.
White wire for the FSK data, black for ground.  I used 32 gauge wire-wrap wire, which I then fed out a hole I drilled in the case so I could button the whole affair back up.
For those who are curious, the signals aren't typical RS-232 style serial, but are synchronous with a single start bit.
A complete packet (with 10ms per horz div)
A closeup of the start bit at 1ms per div, showing the 4 ms and change between the start bit and the actual pager data.

The easiest way to decode this data stream which I now have access to is to feed it into a serial port and decode it with PDW.  Would you believe that I'm just fresh out of actual serial ports?  In the next article in this series, should I find more time to work on this project, I'll write some microcontroller code to capture this data stream and feed it into a computer via something a little more common such as USB.  It should be some interesting code to get it to synchronize to an unclocked stream such as this.

Hopefully once I get that built, I'll be able to monitor pages going out in Northern California, which rumor has it still consists of some fairly interesting snippets of emergency response logistics and sports scores (because we can all tell I'm totally spending today watching some big-to-do sports game instead of writing a blog post...).



Aw shucks, while I've got this pager open, we may as well just do a full tear down, right?
This is the back of the RF board.  You can see the two crystals for the RF and IF oscillators, and the 14 pin socket at the bottom for connecting back to the main processor board.  The bar at the top is the loop antenna
Front of the main processor board.  LCD, buttons, and a battery clip.
Back of the main processor board.  The two gold circles on the bottom right are actually an ICSP header, which you can access from outside the case with a pair of vampire taps to reprogram the pager with a new subscription ID.
I've spent much too much time working with this material at my last job.  This is gap filler, which in addition to giving devices a much more solid and balanced feel, act as a non-conductive heat spreader in challenging thermal environments common for consumer electronics.

A couple useful links on sniffing pagers are the two videos AdaFruit put together on the subject ([1], [2]) and the thesis on the subject by McCulley.

Thursday, February 2, 2012

QRSS and Doppler Effects on Radio Transmissions

 
Thanks in part to our friend down under, Dave Jones, for finally convincing me to buy one, I'm now the proud owner of a second-hand high precision frequency reference (post 1, post 2).  Now desperately searching for justification for the $50 I spent on eBay for my 10MHz Rubidium reference, I figured I'd dust off my extra class amateur radio license, hang it back on the wall, and start playing with RF electronics again.

Possibly one of the most demanding amateur radio modes as far as stability is QRSS, which seems like an interesting place to start, or at least start working towards, since stability is an atomic clock's middle name.

QRSS is extremely slow mode Morse code.  Crazy slow.  Mind-blowingly slow.  Typical Morse code is sent at 12-25 words per minute, and has the rhythmic cadence to it which we're all familiar with via either experience or popular culture (example).  QRSS Morse code, on the other hand, is sent with single dits lasting on the order of seconds, if not minutes.  QRSS is so slow, it's often easier to measure minutes per word instead of words per minute.  Morse code is surprisingly still very popular in the amateur radio crowd, due to its huge advantage over voice communications in challenging situations where you need to deal with high levels of background noise or need to be able to decode very weak stations.

This advantage can be exhaustively explained using Information theory (originally developed by the well-known Claude Shannon), but the argument essentially comes down to a matter of bandwidth.  When you're having a voice conversation with someone else, you need to be able to hear a fairly wide range of frequencies.  Human hearing ranges up to around 20kHz, but it turns out that human speech is actually fairly redundant above a few kHz, which is how telephone companies can get away with only transmitting the bottom few kHz of a conversation.  Your ever-nagging parents are still perfectly intelligible over the phone, but lack the depth and quality of speech which you have to put up with in person*.

Typical voice communications over amateur radio are 2.8kHz wide.  This means that however much RF power your transmitter is putting out is being very carefully spread across a 2.8kHz wide range of frequencies.  Morse code, on the other hand, consists of keying on and off a single pure sine wave, meaning that any spread in frequency is due to simply keying the signal on or off (or poor transmitter design).  Very good Morse code filters are designed to listen to a range of frequencies as narrow as 30Hz.  If you're transmitting a signal, and you can fit it into 30Hz instead of almost 3kHz, you've got an almost 100x power/Hz advantage, making your equally powerful signal seem significantly more powerful and easier to understand on the other side.

QRSS takes this argument to the extreme.  Why waste power splattering your signal over 30Hz of bandwidth when you can instead transmit within only a couple hertz or even less than a single hertz?  Of course, to keep your signal that narrow, you're going to need to send less information, so while typical Morse code is sent at 12+ WPM (words per minute), why not slow that down to the point where sending even just your call sign takes a solid 5+ minutes.  All of a sudden, you can be heard at mind-blowing distances using a trivially small amount of power.



Anyways, back to the point of this article.  So QRSS is crazy slow Morse code, which exceeds the attention span of most mortals.  This means that decoding this painfully slow Morse code needs to be delegated to the ever-patient marvel that is the modern computer.  By feeding the received QRSS signals into the sound card of a computer, they can be decoded and presented as a time vs frequency plot at seen here:
What you see here is a single station transmitting at 10.139990MHz.  The red ticks at the bottom of the frame indicate 10 second intervals, so you're looking at about 5 minutes of airtime.  This was captured from the KK7CC QRSS grabber in Las Vegas at 1:30AM this morning.  (Frequency stability is something that is typically taken for granted, but notice that over this five minute interval the transmitted frequency doesn't change appreciably, which is much of the challenge in QRSS, and where I'll find my Rb reference useful.)

Now notice possibly the most interesting part of this grab; there's a shifted shadow of the beacon which starts about 12Hz high and rolls down to -16Hz over the span of 2.5 minutes.  What the heck is that

It kind of looks like a Doppler shift of the original transmission.  You are most familiar with Doppler shifts from watching ambulances and trains wiz by with the distinctive drop in tone just as they pass you.  This seems to be much the same effect, but we're not talking about sound here, we're talking about radio waves!  Something would have to be going pretty fast to manage to Doppler shift a photon like that...

As a matter of fact, we can even figure out how fast this something is going.  The equation for the observed frequency due to Doppler shift is:
 Given the original frequency f0, the speed of waves through the medium c, and our new frequency f, we can solve for the relative velocity vs,r.  Plugging in everything we already know after looking at the screenshot from KK7CC above and some poking around on Wikipedia, we get:
Now, this isn't quite right; it is probably safe to assume that both our signal source and receivers are stationary, since it's kind of hard to get a couple dozen meters of copper wire hanging between a couple trees moving in pretty much any direction at 400m/s.  Considering that the original signal is still present throughout the window, it's clear that this shift is caused by the radio waves bouncing off of something else, which means that it's experiencing two Doppler shifts; one from the objects relative velocity to the transmitter, and a second from the relative velocity of the object to KK7CC's receiver.  There isn't a perfect way to distinguish these two values without more information, but a reasonable approximation is to simply divide the Doppler shift and resulting velocity in half, giving us 221.8 meters per second, or 496 miles per hour (for the unwashed in the audience).

So I'll leave you with this question: What in the world could possibly be going at almost 500mph, could pass between two amateur radio stations both based in the continental US, and that is clearly conductive enough to reflect radio waves?



* - All humor aside, I disclaim any implication that my wonderful parents nag me in any way, shape, or form.  My parents and I have a very healthy relationship where we trade almost purely logistical emails a few times a month and I venture home a couple times a year for the best cooking I've ever had. <3