μblog: engineering from the trenches

Looks like EMA is looking for beta testers starting next month. Everyone accepted gets early access to the new Orcad/Cadence tools and the t-shirt above. The most comprehensive reviewrs are said to be entered in a raffle for a flat screen monitor. Try your luck.

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As I had mentioned before, I am slowly working on building a “better” Yagi antenna than my previous rough attempt. I have a lot of work related deadlines and I am also moving next week, so progress will be slow. In any case, I decided to start out with the driven element design and then construct the beam and passive elements afterwards.

I am quite fond of the Fonera wifi router, so I am going to design something that can replace its antenna. For this reason, I am going to put a female SMA connector on the end of my feed cable. I have some RG-174/U cable around the lab which is the right impedance, is fairly thin, but is also lossy. For this reason, I am going to keep the feed cable short enough to mount the Fonera comfortably near the Yagi array. The propagation velocity in the cable is 66% of vacuum, so the wavelength at 2.45GHz is about 8cm. Designing the feed cable to be an integer number of half-wavelengths makes impedance matching a little easier so I made my cable 16 cm from the tip of the connector to the loop hookup.

The signal wavelength in air is a little less than 12.5 cm, so I made my loop out of 3M copper shielding tape and soldered the ends of the tape to the shielding and feed terminals of the cable. I tapered the ends to make the loop line up nicely and took care not to heat the end too much as that will degrade the cable’s dielectric core. One side of the tape has glue on it, which will help mounting the loop on a piece of foam to give it a rigid, rectangular shape.

The helpful folks down the hall let me use their network analyzer to measure the antenna resonance, after a little bit of tuning, I got a peak at about 2.4GHz, which should work fine for lower wifi channel numbers. I also compared this to a commercial wifi antenna from SMC which resonated at about 2.43GHz. Unfortunately, I changed the window width when I tested my loop antenna so that is why the SMC antenna looks like it has more peaks.

My next step is to look up an optimal position of 10-14 director elements in literature and figure out how to fabricate the device. I am thinking of using thick copper wire since this will be an indoor unit. Might use the engraver to drill the holes to specifications.

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Today’s IC Friday is another reader-submitted chip. This is cryptoworks six-pin smartcard. The only writing on it is “TUBEAV A”.

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After a few days in the lab, I am finally catching up with things. Over all, I am happy with the way this HOPE turned out and am considering going to the Next HOPE, maybe to present something. At least one reader enjoyed it too! I didn’t take too many pictures, so here is a whole flickr pool from the meeting. The above image is from sushimako. I will summarize my experience in a typical Clint Eastwood style.

The Good:

• A few interesting talks regarding hardware modification. Audience seemed pleased and interested.
• An interesting demonstration by Ladyada regarding how to hook up a used pay-phone to a skype box. These phones seem to be dirt cheap so I am already thinking of a way to wire one up as a bluetooth headset.
• Round the clock soldering training. The “hacker village” people really outdid themselves and provided ample building tools and helped attendees put together the circuit kits they bought.
• Club-Mate, something like a caffeinated version of ginger-ale.
• Hackerspaces in Philadelphia and Washington D.C. (among others) that I will try to visit.
• A comfortable area with to relax in. This featured hammocks and a large display showing some random videos (more on that below).

The Bad:

• Some single presenters were not prepared to give an hour long presentation and would either repeat themselves or end way early.
• Most of the software security talks were low on content and used overly contrived examples. One penetration testing example had the user obtain /etc/passwd and then use a password cracker, I hope it was using a wordlist and not brute force.

The Ugly:

• The overall smell of the attendees forced the organizers to give away deodorant soap bars by the box load.
• A short documentary was played in the rest area depicting an individual who had eight realdolls (wikipedia entry). That is about 50,000USD spent on latex “companions”. At a point in the video, he decided to introduce his dolls to his girlfriend, who tried to deal with them at first, but then gave up and ended the relationship.

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Today’s entry is an old memory chip from Mitsubishi, the M5K4164. This is another chip submitted by a reader, again, all the way from Iceland.

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I am getting ready to leave for New York, NY for 2600’s last HOPE conference. I haven’t figured out all of the talks that I will attend, however, I will surely be going to the 2pm MSP430 talk in Engressia (schedule). If anyone wants to meet up, feel free to leave a comment and I will try to check them periodically. Otherwise, you can simply come find me, above is my latest mugshot.

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As I promised, here is a outline of the steps I go through to make the weekly IC Friday posts. First, a word of caution:

Handling sulfuric acid REQUIRES specialized training and equipment. Misuse can result in serious injury or death. Furthermore, improper disposal can cause serious illness to others and permanent damage to your workspace. Finally, adequate ventilation/fume extraction is a MUST when heating sulfuric acid.

(more…)

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Today’s IC Friday entry is the 8bit AVR micro from Atmega. This chip was sent in by a reader, all the way from Iceland.

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Found the NASA Workmanship Technical Committee website recently while looking at ESD standards. Not much to say about it beyond that it is a good place to look around for general technical information on electronics. Their pictorial inspection reference for examining flight hardware is pretty nice too.

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A frew months ago, I built a small home-server based on a VIA C7 Eden min-itx board. The machine has a 1TB drive attached and runs FreeBSD without any problems. I mostly use it to run some background network utilities and serve up media to the Playstation 3 in the living room. I occasionally stream music from it over a SSH tunnel as well. The lofty ideal was that we would take all of our DVDs (mostly TV series) onto the media server so that we could select an episode to watch without having to go through DVD cases. Ripping the DVDs was not a problem with an external drive, however, encoding the videos into a format that the PS3 could understand was a very time-consuming job on the c7.

This gave me the idea of using a second computer that I have around as an on-demand processing engine. The c7 can rip the DVDs fairly quickly and store the raw files on a network share, it can then wake up the amd64 and queue up the various encoding tasks. The amd64 should process the queue leaving the results on the network share and then turn its self off when the queue is completed. Although my c7 runs FreeBSD, I chose Linux for the amd64 since I may use it to develop embedded images at some point.

The network infrastructure is currently 100baseT, however, I have already bought a 1000baseT switch and cards for all of the machines. I haven’t put the gig-E in place just yet as the network file system (NFS) can serve data more quickly than the amd64 can encode over the 100baseT. Although the amd64 boots off an internal drive and then mounts the NFS, I am thinking of moving it to an 8GB solid state drive, as it only needs the bare essentials to encode videos.

Powering the system down can be easily done in software using the standard Linux/Unix shutdown command. This puts the system into S5/Soft Power-Off mode which doesn’t care if you remove the power. Waking up the system is more tricky. Many of the Wake-on-* features of the BIOS are designed to wake the system from S3, which is a state where all of the system is powered-off with the exception of the RAM. Power can still be removed as the hard drive buffers are synched before the system goes into “standby”. I would really prefer to do a full shut-down (S5) so this is not an option. One work around is to enable the machine to wake up from S5/S4/S3 via PS2 mouse click. I haven’t yet worked this out fully, however, I am thinking of linking the mouse (through some logic) to the wake-on-lan output of the gig-E card, or to some output port on the c7. Alternatively, I can latch the power button to the wake-on-lan port.

The final step is to design a queue system. My current thought is to create a special directory on the NFS partition that would contain automatically-generated shell scripts to automate encoding. The scripts would be generated by c7 and would be intended to run on the amd64 machine, probably via cron job that polls the directory periodically. Once the job is complete, the last line of the shell script can be used to move the script to a completed directory. A second cron job can then poll the queue directory less frequently and issue a shutdown when all of the jobs are completed and the directory is empty. Finally, the mediatomb DLNA server can be configured to periodically scan the media directories and add new files into its database.

So far, I have mostly automated DVD ripping with chapter support, and have somewhat worked out how to generate the queue shell scripts. I am still working out the best encoding option for the PS3 to recognize. I have not implemented the queue control cron jobs or a way to wake the amd64 machine from S5, so that is forthcoming. As usual, any helpful hints or experiences are very welcome.

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