μblog: engineering from the trenches

I have finally obtained Maxwell’s works and will be posting both volumes (~40MB each). The reason that historic electromagnetic works have been posted recently is because I am tasked with giving a presentation on electromagnetic scattering off a perfectly conducting sphere. Once I get things sorted, I will post a link to all of the papers that I worked with, all of which are considered public domain according to current U.S. copyright laws.

( 1873MAXWELL-a-treatise-on-electricity-and-magnetism-vol1.pdf )

( 1873MAXWELL-a-treatise-on-electricity-and-magnetism-vol2.pdf )

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After some work, I have been able to get Maxwell’s theory and wireless telegraphy by Poincare and Vreeland as well as electric waves by Hertz in PDF format.
( 1893HERTZ-researches-on-the-propagation-of-electric-action-with-finite-speed.pdf )

( 1904VREELAND-Maxwells-theory-and-wireless-telegraphy.pdf )

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After a previous post regarding data hiding in a JPEG, I figured I would post some technical information. Here are a pair of documents relating to JPEG compression. Hope they help.

( jfif3.pdf ) ( itu-t81.pdf )

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While looking for a work by Karl Schwarzschild, I came across an excellent site that has viewable references for many of the older mathematical physics text including the 1893 book by J.J. Thomson titled ‘Notes on recent researches in electricity and magnetism‘. Below is a PDF of the chapter that deals with scattering by a conducting sphere.

1893thomson-on_the_scattering_of_electromagnetic_waves_by_metallic_spheres.pdf

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Hiding information in plain sight has allways been an interesting subject. I recently came across a paper, describing Hydan, that does this by exploiting the redundancy in the x86 instruction set. For example, any time you add 50 to a register, you can just as easily subtract -50 and get the same result. By alternating which method you choose, you can encode a 1 or 0 at a rate of 1 bit of encoded data per 110 bits of object code. It is a pretty interesting topic as there are many possible security applications for this and it’s generic enough to be applied to non-x86 instructions. There are, of course, easier ways to hide data. (Save the image above and open it with either unrar or winrar to see the instructions.)

( hydan.pdf )

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After some work, I managed to locate both the original, epic manuscript from Gustav Mie as well as an english translation. Many thanks to Thomas Wriedt’s group.

( mie-beitrag-zur-optik-annalenphysik1908.pdf )

( RAE-LT1873-1976-Mie-1908-translation.pdf )

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In the spirit of all of the recent Playstation furor, I have re-kindled my desire to make a Playstation memory card reader. It seems to be a fairly easy project as is documented on various sites. There are six data pins, so the parallel port has more than enough width to do all of the I/O. Furthermore, only +3.5V is required to drive Sony brand cards and there is available editing software. The only difficulty is obtaining the connector. I am hoping to get one out of a PS1 that I have somewhere at home, however, it looks like other types of connectors can be modified to fid the memory card.

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I mentioned before in my post about the EKK-LM3S811 development board that one of its features is that it can act as a JTAG host to a generic target given the proper software. The easier alternative is to create a clone of the Xilinx parallel download cable. This cable is so basic that it will work with almost any software including jtagtools and most derivatives. Here is the link to the schematics, however, a more detailed description is in the appendix of the Xilinx JTAG programmer guide.

( xilinx-jtag.pdf ) ( adi-jtag-ap.pdf )

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Found this development board by accident. Although the shipping is from China, it is ~50$ for the board alone and ~80$ for the board loaded with uClinux and the drivers to run the peripheral ports. Board features RS-232, 10/100 ethernet and JTAG for access.

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The basic function of analytical electrochemistry is to look at the response of a cell (set of electrodes in electrolyte). This often accomplished with a potentiostat, an instrument that can set the potential between a pair of electrodes and track the current or vise versa. A commercial, and often expensive, potentiostat generally has six to nine orders of magnitude of dynamic range in both current and voltage mode (10pA to 10A and 100uV to 100V for the best). However, if you can narrow down the range that you will be working with, you can make yourself a high-performance and inexpensive potentiostat that works over the range of interest. Since we primarily are interested in characterizing various types of iridium-oxide electrodes, the current range will be 1uA to 1mA and the voltage will be 10mV to 10V, so only three orders of magnitude are required. This can easily be realized with a pair of op amps, one working as a current follower (program voltage and track current) and the other as a current source with shutdown functions and necessary logic to ensure that only one driving op amp is running at a time.

The cell is pretty simple: a working electrode, a reference electrode and a counter electrode. The working electrode is the unit under test where you program the voltage between it and the reference electrode or the current between it and the counter electrode. The voltage is measured between the working and reference electrodes in current program mode and the current is measured between the working and counter electrode in voltage program mode. The working electrode is then subjected to various regimes where the relationship between voltage and current is tracked and is characteristic of surface chemistry. Finally, the open circuit potential can be measured between the reference and working electrode to get the cell’s galvanic potential. This potential is generally the difference of the working and reference electrodes’ standard electrode potentials (notice that Lithium’s standard potential is around -3V, that is why most Lithium-ion cells are 3.7V at full charge). Here is a potentiostat design guide as well as an application note regarding feedback stability. Those who wish to learn more should look at Electroanalytical Chemistry by Bard and Faulkner (ISBN 0824790928).

( std_pot.pdf ) ( potstae2.pdf ) ( an4.pdf )

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