Monthly Archives: April 2010

LED’s as Varicap Diodes

G3ZJO just posted a nice little blog entry about the use of LEDs (which are nearly ubiquitous) as varicaps (which are often harder to find). Lots of people are using these in their QRSS beacons, no doubt in part to the work of Hans Summer which was the first person to bring them to my attention. Someday, I’ll begin to work on electronics again, and I’ll make use of this information.

LED’s as Varicap Diodes – Radio – LF/HF to Microwaves.

A new mobile for my car (or the shack)…

I’ve been wanting to put a ham radio into my car for quite some time. The obvious thing would have been to get a nice 2m/70cm dual bander, but I didn’t really want to invest a huge chunk of change into it at this time, so I decided to go with a simple basic 2m rig. My idea is that even if I decide to upgrade later, having an effective 2m rig lying around isn’t a terrible thing: I could use it for a base station radio, APRS, or even an uplink transmitter for the FM satellites.

So, I settled on the Yaesu FT-1900R. It’s inexpensive ($129) and I’ve had pretty good luck with Yaesu equipment. It was also the subject of a review in the May 2010 issue of QST which just arrived. (Incidently, that review is terrible. It is mostly a list of stuff that you can read directly from the product manual that you could just as easily download from Yaesu directly. I expect reviews to include some insightful commentary, not merely a laundry list of features. Additionally, the author chose to power this radio using the cigarette lighter adapter in his car. Everything I’ve read, from radio to car manufacturer guidelines tell you not to do this. It doesn’t lend a whole bunch of faith in the capabilities of the reviewer.)

I’ll probably bench test this radio when I get back home from Portland. Perhaps I can provide a more helpful review.

Simple, reliable 2.5D photography

I’ve been interested in techniques where amateurs can digitize images and models for quite a bit. This website percolated to the top during today’s relaxing web browsing: it’s pretty spiffy, and is interesting on a couple of fronts, not the least of which is that the author designed the gearbox for tracking a laser using a CAD program which drove a CNC mill so that the parts could be cast. Very slick.

Simple, reliable 2.5D photography.

Milhouse muses from the past…

A couple of years ago, I mused about an “easy” checkers problem which my checkers program Milhouse found to be pretty difficult. Here’s the position again, with White to move and win:

An easy hard problem, or a hard easy problem?

(I didn’t mention the source of the puzzle before, I got it out of one of Rob Pike’s books, not sure which one. It’s puzzle 104 in my collection, but listed as Rob Pike Puzzle #8). As I mentioned before, it takes a fairly deep search to find the solution (28 plies). I had mentioned before that using the MTD(f) algorithm proposed by Plaat would find the solution very quickly, but that my implementation of alpha beta struggled significantly. I thought I’d try this position again to see what headway has been made in two years. Using the normal settings… here’s the output of iterative deepening….

      +1 : [-1038] 0.02s
         : 15-10
      +3 : [-1044] 0.02s
         : 18-14 30-26 14-10
... researching after failing low (-1070)
      +5 : [-1070] 0.02s
         : 15-10 32-27 19-23 28-32 23-19
      +7 : [-1086] 0.02s
         : 18-14 32-27 15-10 27-23 19x26 30x23 10-15
      +9 : [-1106] 0.04s
         : 18-14 30-26 15-10 32-27 19-15 25-30 14-9  28-32  9-14
     +11 : [-1118] 0.13s
         : 15-10 32-27 19-15 12-16 18-14  8-11 15x8   3x12 14-9 
         : 28-32  9-5 
     +13 : [-1133] 0.53s
         : 18-14 32-27 15-10 27-23 19x26 30x23 14-9  25-30  9-5 
         : 31-27 10-6  28-32  6-1 
     +15 : [-1143] 2.18s
         : 18-14 32-27 15-10 27-23 19x26 30x23 14-9  25-30  9-5 
         : 30-26 10-14 31-27 14-10 28-32 10-15
     +17 : [-1143] 8.53s
         : 18-14 32-27 15-10 27-23 19x26 30x23 14-9  25-30  9-5 
         : 30-26 10-14 28-32
... researching after failing low (-1168)
     +19 : [-1168] 46.67s
         : 15-10 32-27 18-14 28-32 14-9  31-26  9-5   8-11  5-9 
         : 17-22 19-24  3-7  10x3  27-23  9-5  20x27
     +21 : [-1176] 143.75s
         : 15-10 30-26 18-22 32-27 22x13  8-11 10-14 27-23 13-9 
         : 23x16  9-5  31-27  5-1 

In other words, after two and a half minutes of searching, the computer still thinks white is screwed, with a score of -1176.

I wanted to go back and re-enable the MTD(f) algorithm in milhouse, but somehow through the 100 or so modifications that I’ve done since then, I’ve removed that code entirely. But I thought that I might make some small modifications to the program that would significantly enhance its ability to solve this puzzle. Milhouse normally uses a windowed search to find the best move using iterative deepening. It searches at increasing levels. Each time, it sets alpha and beta (the search window) to be centered around the current value with a search window witdth of about one quarter of a man. If the search returns inside that window, we know its precise value. If it returns less, we “fail low”, and if we really wanted to know what the value was, we’d have to re-search to find it by using different bounds (I normally use -INF to the new failed bound). Similarly, if it fails high, we might need to research.

But in our case, we don’t really care if we fail low. We know if we do that no winning solution can be found at that depth. There is no reason to try to find the exact value, we may as well just deepen the search and try again. So, I made some minor modifications to the iterative deepening procedure. I basically set the alpha cutoff to a high value (say 1000), and if we fail low, then we just continue without researching at the next depth. This is very similar to what mtd(f) does, except that it uses null-width searches. Here’s the trace:

... researching after failing low (-1038)
... researching after failing low (-935)
... researching after failing low (-926)
... researching after failing low (-818)
... researching after failing low (-722)
... researching after failing low (-715)
... researching after failing low (-616)
... researching after failing low (-602)
... researching after failing low (0)
... researching after failing low (0)
... researching after failing low (0)
... researching after failing low (0)
... researching after failing low (0)
... researching after failing low (222)
     +29 : [9973] 1.76s
         : 19-24 20x27 18-22 17x26 15-10  8-11 10-6   3-7   6-9 
         : 12-16  9-6  16-19  6-2  19-24  2-6  11-16  6-9  16-19 
         : 9-13 19-23 13-9   7-10  9-13 10-15 13-17 15-18 17-22
final score = 9973
1.757 seconds elapsed.

In other words, in less than two seconds, it finds the winning line. Very cool.

Great Science Videos: Sixty Symbols

While mucking around this morning, I bumped across the Sixty Symbols website, something I hadn’t seen before. It describes itself thusly:

Ever been confused by all the letters and squiggles used by scientists?

Hopefully this site will unravel some of those mysteries.

Sixty Symbols is a collection of videos about physics and astronomy presented by experts from The University of Nottingham.

They aren’t lessons or lectures – and this site has never tried to be an online reference book.

The films are just fun chats with men and women who love their subject and know a lot about it!

It’s worth noting many symbols have multiple uses across scientific disciplines and we somtimes tackle them from an unexpected viewpoint.

Click on “gamma” and you’ll find a professor of physics talking about cricket balls… Click on “rho” and we’re stuffing paperclips into coffee cups.

And sometimes when there’s no symbol to tell a story (like Schrödinger’s cat), well we just make one up!

However whatever symbol you click on, we hope you’ll see something interesting and maybe learn something new.

As example, check out their explanation of the drinking duck:

Great stuff,

Sixty Symbols – Physics and Astronomy videos.

Addendum: The original patent didn’t include the most important part of the drinking bird: his ubiquitous top hat!

Q: Are there any good, open user interface options?

Yesterday I was in our Atrium, and Craig had his iPad with him. I got into a discussion with him and Loren about why I thought the device was very cool. (I also told them why I had been actively discouraged from becoming an iPhone developer earlier, but that’s a story for a different time.) But I brought up a point which I’ve been kind of mulling over ever since: the iPad (and iPhone) may be the first not-completely-user-hostile-interface ever delivered in a consumer electronic device.

Consider your TV set and its remote as a counter example. On virtually every television ever made, there are two ways to select what channel you wish to watch: by going up and down, or by entering a channel number. There is no more reason to select channels this way than there would be for you to access your online photos by number, or by paging through them one at a time. And yet, for decades, no TV manufacturer has sought to upgrade this very simple, basic interaction that you have with a television. Is there really any reason at all for you to use channel numbers for anything? They add ten buttons to your television remote. Wouldn’t it be nice to remove that space, and use it to make the buttons you actually do use larger, and differentiated so you could actually use them in the dark? And how about those buttons to scroll up and down lists? Wouldn’t you just like to point at what you want? The Nintendo Wii uses a nice IR sensor system to select items: imagine of that technology were merged with your remote, along with accelerometers and the like. If Nintendo can profitably make these as options in a $250 game system, you’d think that that kind of technology could be used in other consumer electronics.

And don’t even get me started about devices like Blu Ray players. Why do I need a different remote? And a completely different system of conventions and menu selections. Bleh.

Okay, I’m getting a bit astray. The iPad has already demoed some really, really nifty applications with interesting, intuitive interfaces. But while I have defended the iPhone/iPad as a consumer device, I am not really all the enthusiastic about doing my own programming and experimentation with such a device. So, I thought I might throw out this question: imagine that you were going to prototype improved interfaces for media devices. Are there any open source options that are worth considering, or are they all terrible? I’m considering a platform like the Acer Revo, hooked to a large screen TV using HDMI, and possibly some wireless bluetooth devices (or maybe just the Wii remote). Anyone have any experience/success with this kind of interactive UI programming?

Shame on You: An Open Letter to Gizmodo

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