μblog: engineering from the trenches

Single BiFET op-amp from Analog Devices. Looks to be pretty planar when I scanned the Z axis with the confocal on. (datasheet)

ad711-10x.jpg

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I am turning 25 today. Clearly, all subsequent posts will feature an increased level of maturity, sensibility, and overall proffessionalism. Also, clearly, the next IC Friday might have to become IC Saturday. Please enjoy this audio amplifier datasheet from 1982.

( tda2611.pdf )

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This is a follow-up to my previous post where I was trying to assemble a HEMNES set of drawers from IKEA. Long story short, I tried to put it together, but noticed that it was missing the instructions and the slide rails for the drawers. After going back to IKEA to get those pieces, it turned out to be that those were the only pieces technically missing, so Steven technically wins the microcontest. Upon finally assembling the unit, I was amazed at the total degree of incompetence and neglect that IKEA has put into this product. (I am not the only one.) With the help of a coworker, some extra woodworking tools, two CAD programs and the use of our lab’s MATLAB cluster, we were able to put together this set of drawers. I will now outline the modifications to make this work following the flow of the manual (included at the bottom with annotation if you don’t have it) .

The first thing that is apparent is the lack of proper fastener holes in the two side pieces. It is easy to start with the bar that goes across the front connecting the left and right walls of the HEMNES. It was straightforward to drill the hole for the fastener so that the bar is flush with the rest of the chest. Unlike the instructions, there was no second hole in the side of the bar for the wooden dowel, so this will also have to be drilled if you want to use it. It is also fine to put some good wood glue in the seam and tighten the fastener and leave it at that. The middle piece that holds the two smaller drawers on the top is also missing a hole in the back for the screw, so we used the strap that is used to secure the chest to the wall to keep it in place. Drilling a new hole and putting a large wood screw in that place would have been better, but we didn’t have the right size screws around to go through the whole beam and the top drawers won’t hold too much weight, so this was an okay solution.

The drawers were whole new type of madness. The slots that the bottoms of the drawers were supposed to slide into were not cut right so the left and right slots were aligned and were about 1/4″ above the back and front slots, which were also aligned. On the two smaller drawers, some of the holes that the fasteners were supposed to screw into were too big, so I cut some small plastic pieces to use for filler and then screwed in the fasteners. Once I put the bottoms in, the holes at the back of the drawers didn’t line up with the pieces of wood, so we used wood screws where the plastic pieces would not fit. On the bigger drawers, the sides had three holes and the back pieces only had two holes in different places, so we were forced to use wood screws to hold the drawers together. Finally, since the drawer bottoms did not fit in the front slot, we put a few wood screws in the back of the front faces to hold up the bottoms.

The next step was aligning the slide rails for the drawers. The top large drawer was hung about 3/8″ too low, so the left and right slides on the inside had to be removed and moved up slightly. Since the spacing is really critical, we had to re-drill the holed and use the original screws so that the rails would not have anything for the drawers to catch on. The top drawers were also hung crookedly and the rails on the middle piece that supported the two small drawers had to be raised about 1/4″ so that they would become even.

Finally, there were absolutely no appropriate holes to secure the top of the chest onto the rest of the chest so we just glued it on. We put a bead of Tightbond wood glue and stacked some books on the chest instead of using clamps. The result secured the top on and generally made the drawers more sturdy.

( ikea-hemnes-instructions-annotated.pdf )

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Last week, June bought a HEMNES chest of drawers from the IKEA in Washington, D.C. which we brought up to State College, P.A. Upon opening the box, I noticed that the assembly manual was missing. Having an undergraduate degree in IKEA furniture assembly, I thought that the assembly would be an easy task even without the manual. I soon found out that there were a few critical pieces missing, and not the kind of pieces that I could easily manufacture in the lab. I took these pictures so that I could compare what I have to what I should have to be able to build this thing then I go back to IKEA DC later today.

The contest is simple, be the first to figure out what is missing from the complete package and leave a comment. I already know one thing that is missing and will hopefully know the rest of the missing items later today. For the prize, I will send you something small from my office and recognize you on microblog. Caveat: I will only send to U.S. or Canada, sorry everyone else!

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Since the Virtual Slice software has not yet been installed on our scope, taking images of large, complicated chips and reconstrucing the montage in photoshop is a pain. For this reason, Ihave elected to uncap a ubiquitous, linear voltage regulator of unknown make: the 7906. Hopefully we will get the software in place soon, otherwise it will be op amps and related circuits for the next few weeks.

7906-10x.jpg

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Since I am not interested in shaping the Wii wireless network traffic further than I already have, I am moving on to modifying the provided Linksys firmware for the WAP54G access point. The very first step is to examine the filesystem to see what tools are available and how I might be able to hack a telnetd or something into it. The second step would be to download the sources from Linksys’ GPL code center.

After downloading the 2.08 firmware, we have a readme and a .trx file. The TRX file contains the kernel at the start and a cramfs (compressed ram filesystem) image at the end. The trick is to find the start of the cramfs image, and a good one to use can be found on this Seattle Wireless page. We look for the start of the cramfs magic number (3d4528cd), calculate the offset to it from the start of the file (0×0095f00 = 614144, add 12 for the offset to 0×3d45). Mounting the filesystem is pretty straightforward on a Linux sytem to read the contents. If you are too lazy to dedicate a machine, download the free VMware server, register it to get the serial code, download a Linux ISO and install it in a virtual machine. Most kernels come with cramfs pre-compiled and most systems with modest development tools will have hexdump.

( contents of the 2.08 WAP54G firmware: tmproot.zip )

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