μblog: engineering from the trenches

I have made few attempts to keep this space updated and relevant over the past year, but ultimately failed. I have nearly completed my PhD so I have gotten extremely busy with finishing experiments and writing/editing my thesis. I still do analog and digital design in my day-to-day life, except, most of that work cannot be published here directly. I no longer plan on updating microblog, however, I will leave it up for at least the forthcoming months until the end of the internet in case anyone is interested in saving some information. Thank you readers, it has been a great ride!

Update: I had no idea that there were so many readers, so I will not disappoint and will do my best to keep this content up indefinitely. I may add in the future, but it will not be nearly as frequent as it was in the past.

P.S. I will be looking for an industry job in medical device design in the coming spring, so don’t hesitate to contact me if you are looking for an engineer.

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I had the good fortune of running into someone who read IC Friday, at random, and that reminded me that I have been quite delinquent in updating ublog. My work load has tripled over the past few months, so I have been busy, however, I will make every effort to keep this current. Below are my non-work-related engineering projects that are in various state of completion, hopefully I will create writeups for them and you will find them interesting.

• DJ Box — Mini-itx fanless system with wifi to encode and stream, on the fly, audio from my turntables. Welding a custom case (see below) and adding one or two analog VU meters.
• MIG Welding — Might not really be considered engineering, but at least it’s arc welding. My family got me a 140A MIG welder for my birthday in February and I purchased everything needed for steel and aluminum welding, so I will try to make something interesting. Maybe use it to destroy some solid-state relays (on video).
• Functional IC Decapping — IC Friday will not be continued in its former state where chips were bathed in acid and imaged. I think it will be better for everyone, especially myself, if I create fewer but higher-content posts. I am thinking of either decapping some analog circuits without destroying the majority of the package and demonstrating some optical glitching, for example. Another idea is to image the chips but write a clear post on the identification of various sub-circuits on the IC substrate.
• Sleep-State Staging EEG Amplifier — I am have been looking at the most simple method to create an EEG amplifier and LabView combination that is capable of discriminating sleep states. I am then planning to post some data from myself.

Feel free to post a comment if there is something specific that you want to see written up, hopefully I can get to it in a reasonable manner. It’s good to be back!

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I have hopped onto the Twitter bandwagon and created an account for my FreeBSD media server. My goal was to have the machine check Twitter periodically and send any tweets designated for it to a small thermal printer. This way, if I wanted to remind myself to pick up some milk and bread, I could send a tweet @routed and it would be documented. I bought a Verifone PrintPak 300 credit card receipt printer off eBay for a very reasonable $20 shipped. This printer was small and had an RS-232 interface (see cable pinout below). Although the printer would like hardware handshaking, I just tied the RTS and CTS pins together on the printer and was sure to wait one second between printing lines in my script. The cable has mini-din on one end and DB9 on the other end, however, it is straight forward to make a DB25 cable as well. The software control is done by a small Perl script (also below) designed to run on a UNIX/Linux system that checks friends timeline every few minutes and prints any new posts to the serial port. It is not very intelligent and does not convert dates/times to the local time zone (unless you live in GMT). My future plans are to make this printer wireless using one of the TI RF/USB development boards so that the printer can go on top of the kitchen refrigerator and the media server can stay in the office.

Feel free to post your twitter account in the comments and I will have the server follow you so that you too can add grocery suggestions.

(twitter-prints Perl code)

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I have been looking at getting a netbook for some time, specifically the Samsung NC10. I have been looking around for a netbook with the best performance and noticed that the “best” netbooks from all manufacturers seem to have the same specifications (at the time of writing):

• 1.6GHz, N270 Atom processor (single core)
• 1GB Ram
• 10.2″ LCD (no touchscreen)
• 160GB magnetic/16GB solid state storage
• Windows XP Home

Have the manufacturers gotten lazy and all ended up using the same reference design? A little bit more research and found out that this is related to Microsoft’s reluctant extension of the XP availability. Microsoft has agreed to provide OEMs with very cheap ($32, $26 for developing countries) XP Home licences for “ultra-low cost PCs”. The downside is that ULCPC’s hardware specifications cannot exceed some guidelines set by Microsoft which include the list above. On one hand, these XP Home licences are every affordable thus making netbooks affordable for those who want to run XP, however, ULCPC licensing definitely caps performance for all netbooks across the board. I would rather get one with 2GB of ram and use FreeBSD or Linux.

In the end, I decided to hold off on getting a netbook and upgrade my home theater system instead. I am looking forward to CES 2009 (1/8/2009-1/11/2009), hopefully there will be some announcements of netbooks that are not bound by ULCPC standards. I would really like to see a machine with the forthcoming dual core atom chip, 2GB of ram, and 5+ hour battery life for about $500.

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I am presenting at the 2008 Society for Neuroscience Conference next week so I finally got my credentials in the mail. The conference has had a pretty substantial vendor area and I don’t think that it will change this year. In the past, all of the vendors would try to give away anything from pens to yoga mats to anti-epileptic rectal gel applicators (without the gel) with their company names on them. All you had to do is let them scan the 2D barcode on your badge so that they could add your information to their marketing database. I don’t like collecting those things as they are usually really poorly made, however, this year I am going to have some fun.

I scanned my badge and used the SWIPE toolkit (online tool) to decode the 2D barcode and see that it contained things like my SFN member number, name, address, and contact information. The specific format of this 2D barcode is PDF417, so there are several available on-line encoders [1][2][3]. My plan is to encode myself a new barcode and stick it over the original barcode in the badge holder and then see if any of the vendors notice. I would even let them scan my badge without giving me anything in return.

If you want to meet up at the SFN conference or have an idea for credentials to put in the bar code, send an email or leave a comment. I am thinking of impersonating Carl Gauss, but don’t know what to put for his phone number or email, maybe I will leave them blank.

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I have been very busy at the lab lately, too busy to update ublog regularly, and this set of formulas from Gamma Instruments has saved me a bit of trouble. Several air core inductor designs are outlined which allow you to make your own custom inductor, within reason, if you need to test something and you don’t have the part on hand. Typically, the inductance values will be modest, however, it is much easier to make an inductor yourself than a reasonable capacitor. Just think of all of the folding!

( pancakewheel )

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I have been reading James Gleick’s Chaos and I must confess that I am very impressed with the book so far. I am beginning to realize some of the practical applications of non-linear dynamics to analog circuit design, however, more on that later. What has been very interesting is the slow change in the mentality of the scientific world, from the notion that a small change in a systems initial conditions only warrants a small change in the output, to the reality that small changes in initial conditions can generate wildly different results. One of the pioneers in this field was the late Edward Lorenz. He discovered that a slight change (less than 1%) in the initial conditions of his deterministic weather model, which was numerically integrated, would cause the outcome to diverge from the unperturbed simulation to the point that the two weather systems were completely different after several days. The error in his integrator could not account for this disparity, therefore, he went through some analytic computations and found that simple differential equations can have very complex behaviors that were very dependent on initial conditions. He published his results in the Journal of Atmospheric Sciences, a paper that is well worth looking over. For those who are not mathematically inclined, looking over the introduction and conclusion should provide some insight into the paper. Additionally, this is the paper where the often duplicated Lorenz attractor, or butterfly attractor (figure 2) makes its first appearance.

( 1963lorenz-deterministic-nonperiodic-flow )

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I recently read a statement somewhere along the lines of “you always want low equivalent series resistance (ESR) capacitors in your design” which got me thinking about ESR and capacitors in general. The truth of the matter is that you do often want capacitors with moderate ESR (>10 Ohms) for bypass applications, especially in voltage regulation circuits. The main reason is that the capacitor introduces filtering (a zero) into the circuit just through its own capacitance and series resistance, and this filtering can be used to stabelize the feedback of a voltage regulator and prevent ringing/oscillations. AN-1148 is a great application note from National semiconductor that gives an overview of feedback in voltage regulation and frequency domain analysis.

Once the concept of adding a zero to the frequency response of a circuit is clear (see this app note if it is not), it should be apparent that this is exactly the reason why designers put several bypass capacitors in parallel when decoupling a complicated integrated circuit. The IC injects a known set of frequencies into the power system and the designer tries to use each of the capacitors, with a unique zero, to try to filter out each frequency individually. This works well for circuits with precise clocks, however, an RC oscillator can have plenty of drift so it would be advantageous to use capacitors with higher ESR which lead to lower Q values and broaden the range of frequencies which they filter out most effectively. This follows the notion that you should not use high quality components to filter a low quality circuit, all components should be of the same quality.

( an-1148 )

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Penn State University has decided to roll out an ebook reader program by making the PRS-505 portable reader from Sony available for checkout. The program became quite popular and I was unable to get one myself, however, a colleague managed to secure one so I was still able to play around with it for a few weeks. My main goal was to test the reader’s capability of displaying datasheets and scholarly journals.

In short, I was a bit disappointed when I could not clearly read either without converting each page to an image first. It was pretty clear that copying a simple PDF to the device, although it does have some basic PDF viewing capability, was not going to result in something readable. In the case of the journal article, the device would split text in a strange way which sometimes resulted in fragments of words alone on a page. Scaling some datasheets to make them readable crashed the device requiring a hardware reset. Two positive notes are that the ebooks that were loaded on the device displayed really well and that the device was able to reproduce color JPEGs as fairly detailed grayscale images.

I hate to end this review on a negative note, however, this device is pretty useless for my needs so I will wait for the next model and hope.

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I have been doing a lot of signal processing/statistics lately, however, I still design PCBs using the Orcad suite from time to time. PCB Editor is both powerful and feature rich leading to massive frustration every time I forget the exact steps for generating the necessary artwork to submit for manufacturing. In an effort to combat this overhead, I documented the specific steps and am publishing them online in the hope of saving someone else the same frustration. These were noted down fairly quickly so please let me know of any errors.

allegro-gerber

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