μblog: engineering from the trenches

Today’s IC Friday will focus on Microchip’s PIC12F629.

pic12f629-10x-stitch.jpg

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As promised before, I have finally worked through the majority of this paper, enough to give a brief introduction and discussion.

The key point of this paper is to demonstrate the importance of statistical analysis and its applications to determining information generation and transmission capacity. The measure H, or entropy, can be thought of as the amount of variance, or uncertainty, in a communication system. This leads us to define the theoretical capacity of a communication system given the known statistical properties of its constituents as well as apply analysis to practical systems.

The concept of information entropy deals with the uncertainty in the expected value of this information. Although it is rooted in statistical mechanics, it can be seen that highly predictable information has low variance, and therefore lower entropy, as compared to more random information. From this measure of information entropy, we can determine the necessary number of bits to efficiently encode this information, or to put it another way, how many symbols we can transmit per bit (assuming digital communication medium). Although the case of uniform probability distribution for all information symbols is easiest to analyze and leads to highest entropy, most practical applications have particular statistical distributions for symbol/information generation. Shannon goes to lengths to demonstrate this with the English language noting that selection of letters, or even words, is highly structured and far from random. This structure is a measure of redundancy of information, so that if I typ like ths, you cn stil undersnd me. (Spammers have been rediscovering this fact for years.)

Once the information entropy for all of the circuits involved in the communication system are determined, the channel capacity can be determined in the form of symbols per second given a finite certainty and a raw channel bit-rate. Shannon gives a fine example of a digital channel operating at 1000bits/s with a 1% error rate leading to an effective bit rate of ~919bits/s to account for error detection. Some communication system examples are given which I will not discuss in depth, however, I will try to reiterate the important steps in efficient communication design. Although Shannon gives a mathematical formulation for determining the theoretical limit for channel throughput, it is up to the designer to realize create a system which comes close to the limit. To do this, it is imperative to know the statistical properties of all of the sub-systems involved and the noise that may be present, and only then can efficiency be achieved.

The paper is by far more in-depth than this introduction and the math is not too hard, if anything, it is worth a look-over for some commentary on the statistical nature of the English language. As always, feel free to post a comment to discuss something about the paper, add something, or correct a mistake I have made. As a small bonus, I am adding Shannons’ patent for PCM-encoded voice/telephone service for those who like to read those types of things.

( 1948shannon-a-mathematical-theory-of-communication.pdf )
( 1946shannon-communication-syste-memploying-pulse-code-modulation-patent.pdf )

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This time, we have the AD633 four quadrant multiplier chip from Analog Devices. I have used this device in various places (including for the power measurement circuit) and have been quite impressed with its linearity. This could be, in part, due to extensive resistance matching through laser trimming.

ad633-10x-stitch.jpg

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I decided to install Vista on my home workstation today in hopes of determining which software that our lab group uses will work fine and which will have problems. To be more specific, if the data collections will continue to run on Vista machines. This test was partially motivated by a growing of support for Vista drivers and neglect for XP drivers by hardware manufacturers.

The system under test is an Athlon64 3200+ with 2GB of RAM and GeForceFX 5600 graphics adapter. The software tested will be MATLAB 2007b/2008a, LabView 8.2/8.5 with PCI-based DAQ, Cadence/Allegro 15.x.

The very short time that I have used Vista (on this machine) has been mostly pleasant. The good is that everything seems to work fairly smoothly and all of the hardware was identified at bootup and all drivers have been loaded. The main downside is that Vista has needed my permission for almost every action.

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I have found a FireFox addon that essentially allows one to highlight the text to be translated, right-click,  and see a preview of the translated text. One more click opens a tab with the full Google translation of the text. Thank you, Pau Tomàs, for making my life a little bit easier!

( gTranslate addon )

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Today we have the Rambus RDRAM chip from the Playstation 2. Not too interesting, not even a logo.

ps2-rdram-4x-stitch.jpg

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Some time ago, I wrote a guide for compiling OpenWRT firmware for the la Fonera router. I began to really like OpenWRT and decided that I may want to put it on some other devices I have around, namely a Linksys WAP54G and WRT54G. I could have modified my development suite, however, I figured that it is better to let someone else do the work this time. Freifunk has done just that and has posted modified OpenWRT images that will even fit on the limited WAP54G. I have one of the TRX files loaded on my version 2.0 WAP54G and running without problems. The only slight hickup was that the Linksys firmware did not want to “downgrade”, so I pointed the a browser to http://router_ip/fw-conf.asp and disabled both check there and then simply uploaded the new TRX file using the updater. When everything was done, the router was back up on the same IP and was accepting ssh connections with username “root” and password “admin”. [I previously posted the password was "password", that is incorrect, sorry for the error.]

[ Image is from KJH.com ]

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We got some new drives in the lab today and I accidentally looked at the power consumption of these 1TB SATA drives and discovered that the +5V line required 700mA and the +12V line required a mere 550mA to operate. I compared it to 200GB Maxtor drive and noted that the +5V rating was about the same, however, the +12V rating was 1500mA. The 12W power rating reduction is impressive. WD’s product specifications page notes that read/write power is about 7W while idle power consumption is around 4W. Anandtech claims that Seagate’s 1TB drive is also fairly efficient. Please understand that I have no financial interest in selling these drives, I am simply impressed that we can get 1TB of storage in such an energy-efficient footprint. Combining this with one of an energy-efficient x86 system could soon become the new trend in always-on home media servers.

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It’s that time of the year again when I celebrate my birthday. Instead of spending time at the fume hood uncapping chips and behind the microscope, I have slacked off and have spent my limited free time behind the EGX-300 engraver fabricating a some parts for a birthday present from me to myself. June was nice enough to make me a cake with icing leading to the terrible pun. The cake was great and normal IC Friday will resume next week.

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I have been working on spectral analysis of time series data and I am finding that (duh!) it is often easier to use someone else’s wheel than to invent a new one myself. That is, if their wheel has all of the necessary features and meets your performance criteria. I have been working with multi-taper spectral estimates and have found that the Chronux code (MATLAB scripts), available from Partha Mitra’s lab, to be fairly easy to use and effective for some continuous time-series analysis. The code also handles point process analysis, however, I don’t use that feature much.

The main reason that I like to use the multi-taper methods based on Slepian tapers, is that each taper gives a independent measurement of the signal spectra which then allows for computation of variances and therefore confidence intervals. This gives a certainty measurement to the analysis which can either make a strong case for its significance or will identify deficiencies in the data. Basically, these people put some years into writing this code and if you need to do coherence or spectral analysis in MATLAB, might as well give it a try.

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