μblog: engineering from the trenches

The short answer is to put a SMA connector on it. From an RF standpoint, many of the USB WIFI adapters have pretty decent chipsets that are used to make up for their small antennas and limited board availability. In the case of the DLink DWL-122 (yes, I mis-spelled it on the board), the choice is a small f-strip antenna. The feed port can be identified by the tapered, triangle-looking trace, so that is where the SMA center feed will go. The other pad is for the return and will be connected to the outside of the SMA connector. Now that the USB device has a standard RF port on it, it’s quite easy to experiment with some personal antenna designs. The performance is not optimal since the tapered feed pad along with the SMA connector will create an impedance discontinuity, but it is quite easy to get better performance with simple designs. Below are comparisons of the signal strength with the f-strip and the whip antenna from the Fonera.

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** UPDATE ** The laser is gone, sorry!

I have been cleaning and found the need to get rid of a few things that I will never use. A couple of things that I would like to get rid of are a Melles Griot helium-neon 632.8nm 5mw laser. The laser is 5mW, on the order of a red laser pointer, but has a much better quality factor and is pretty good for laboratory use. It is free to the first person who claims it by email or comment AND pays for shipping. I am in the USA zip code 16802, the package will be 1.5 LBS at most and the size will be a little smaller than a shoebox.

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It is not news that Sony has settled its disputes with Immersion over the rumble features in the PlayStation controller products. According to an interview taken at the God of War II release party, God of War III should have rumble features on the PS3 (see the 9:40 entry). It is good to hear that rumble is no longer “last-gen” technology and that it will be compatible with the acceleration sensing features of the SIXAXIS. I couldn’t find information on who makes the accelerometers for the SIXAXIS, but it looks to me like a Analog Devices package (more so than Freescale or ST). If this assumption is correct and the chips are a derivative of Analog’s ADXL line, then they should be a set of DC sensitive MEMS devices so it may be possible to determine controller tilt just from a time-averaged accelerometer signal. Furthermore, if the rumble design is the same as in the DUALSHOCK controller, it may be possible to band-block the motion artifact due to rumble features from the acceleration signal to retain both the slow tilt components and the quick jerky movements. So all in all, I am not convinced that the two systems are wholly incompatible beyond the fact that any appreciable rumble feature would eat battery life resulting in a heavier controller, but I figure some people might actually enjoy that. This and the PlayStation Home features might turn the PS3s into more than a BlueRay player. I guess I will keep sticking to my view: there is nothing better for the consumer than a console war between several companies. (Controller pictures are from IGN.)

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Some time ago, I posted the schematics of Xilinx compatible parallel port to JTAG cables. Since then, I found more schematics that describe a complete Spartan-3 (or 3E) board including the same programming cable. These schematics include an FPGA (which can be as small as 100TQFP) and an SRAM chip with the intent of re-programming the setup at every powerup using JTAG. This can be extended by looking at page 67 of the V3.4 Spartan-3 datasheet. There are several methods of adding a configuration ROM to the device to ensure independent operation on power-up. Finally, the Xilinx ISE WebPACK can be downloaded to create basic bitmaps and actually send the code across providing a fairly limited, but free, development platform. Unfortunately, the Lattice Semi’s parallel port to JTAG cable is highly guarded proprietary information, so the same type of almost-free development solution is some ways off.

( livedesign_eb_schematics-xilinx_spartan.pdf )

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As I am preparing for exams, I am appreceating access to excellent books more and more. As a result, I have created a second site aimed at listing technical books that people find to be most helpful. It is my assumption that everyone has at least one favorite book on a technical/scientific subject whose title they could share with the rest of the world. If the site takes off, I will try to get a sponsorship deal with an on-line book retailer (amazon/bn) and use 100% of the proceeds to get the contributers gift/discount cards so they could in turn get more excellent books. If you have some books that you think are worth-while, please take some time to register and write a short post about them.

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These are die shots from the Nat. Semi’s 16 input programmable AND-OR gate array. Everything is pretty standard, 25ns propagation delay.

( pal16p8a.pdf )

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I just noticed that Tektronix has a special section on their website that is dedicated to aiding teachers with classroom and lab resources. They have some documents that are aimed at teaching people how to use their scopes, whose contents can easily be applied generically to scopes from other vendors. They even have (a first in a series) pamphlets that are aimed to give a basic overview of some electrical engineering terminology. Although they are trying to sell their products, the information contained is pretty universal. (Picture is from UMD.)

( 3gw_17276_0.pdf )

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In exactly two weeks, I will be taking the written portion of my graduate school qualifier exams. The first day will focus on applied math and the second day will focus on electromagnetic theory. The next few weeks will be focused on solving problems and polishing my knowledge of the theory, so some of the posts may be more theoretical in nature. Another consequence of this preparation is that I will be very justified to take a break from studying to answer any questions that readers may have in the fields of applied engineering mathematics of electromagnetic theory, so feel free to email them or post them in comments. The time frame for this is until the completion of the oral part of my qualifiers on 12th April, at which point my brain will probably explode.

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My office-mate recently told me about a very simple motor that can be made from a magnet, AA battery and a piece of wire, so I figured it was time to look it up. One such design was found on  dangerouslyfun.com, a web site with a few clever how-to guides (with videos). Although well laid out, the guide is a little light on the theory of operation, so here goes.

The Lorentz-force equation states that the net force (F) resulting from a magnetic field (B) on a particle with charge (q) moving with velocity (v) is :  F = q(v x B), where x is a cross product. To put simply, the force is maximal when v and B are at right angles to each-other, and will be orthogonal to both v and B. The coin shaped magnet probably has it’s north and south poles oriented on the flat, round faces, so the lines of magnetic flux (or the field lines) go from south to north (animated gif). Since electronic current is nothing more than the flow of electrons, their velocity is most orthogonal (or closest to 90 degrees) to the B field in the flat bottom wire segments of the top figure. The force exerted on the wire segments is then either forwards or backwards in the plane of the magnet depending on the flow of the current. To make things clear, the magnet is connected to the negative terminal of the battery and is used as a current return path from the positive terminal via the wire. The result is that the wire loop spins, not unlike a more typical electric motor. The authors of the original howto suggest that rare-earth magnets are used as typical ceramic magnets are too weak.

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Today we have the 7202 Asynchronous FIFO buffer from IDT. There are some initials from the designers of the chip as well as an American flag signifying the country of origin.

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