Wednesday, March 31, 2010

Sensing, Information and Accountability

Below is a screenshot from the Fabfi status page a couple days ago. The astute reader will notice that the only nodes on the "backbone" are up. If I had also included screenshots from the proceeding 6 hours you would see blocks of nodes blip off the map one by one and then a few (battery powered?) lingerers clinging to life for some hours before joining the rest of the city in a total blackout.
This got me thinking about data collected by the fabfi network as a means to community and government accountability. The fabfi network is growing rapidly. With over 40 active nodes, the user-base is easily now into the hundreds (considering the size of households and the fact that users often share with neighbors), and with the newest connections is spreading geographically across most of the city. Fabfi is a ready potential forum for collaborative community organization. Network stats data useful for keeping the power on and the air clean? (imagining USB air quality sensors). What is the interface that best facilitates dialog and community building between fabfi users?

Have ideas? Send them our way...

Sunday, March 28, 2010

Better reflectors 101

As the news-media seems to have noticed recently, Fablabbers in Jalalabad have been designing and making their own reflectors out of bits and pieces they can pick up cheap, putting reflectors together for less that $3 US. This week brought two more such reflectors online. As you can see, the design is starting to take on a more clearly defined shape and bill of materials. The hole punching in the reflective surface is both functional and artistic, as the holes reduce the wind load on the installation:


Since the Fablabbers are usually reading along, I thought I'd dedicate a post to what makes a good reflector and some nifty ways to make a little bit go a lot farther. I preface this little tutorial with the statement, "I am not an RF engineer" (I am neither a whiz at physics nor a practitioner of voodoo, one of which is usually required for good RF engineers), but I do know a couple of things about making reflectors that are worth sharing.

The basic shape of nearly every dish-like RF receiver you see out in the world is that of a parabola, as shown at right. The unique property of a parabola is that everything entering it perpendicular to its opening is reflected to a single point called the focus similarly to the way a funnel directs all the liquid poured into it into a central hole. By putting your transceiver at the focus, you redirect any RF energy that would have missed your transceiver right back to where it belongs. The drawing above-right is an example of a parabola in a single plane. It will collect and redirect energy to the left and to the right of the focus back to the transceiver.

It is easy to draw a parabola in a single plane without using any math or special tools. All you need is an L-shaped straightedge such as a carpenter's square, a second straightedge, a pencil and some string:

  1. Lay the straightedge on the edge of the surface you want to draw the parabola.
  2. Fix one end of the string to a point you want to be the focal point (F)
  3. Fix the other end of the string to the top of the L-shaped straightedge (B) so that the middle hangs below the focal point as shown in the drawing below
  4. Place your pencil inside the loop.
  5. Slide the L back and forth while holding your pencil against the L. The string will make it go up and down.

A quick look at the latest reflectors shows they are not truly parabolic, nor is the active antenna centered in the design:


These reflectors could be much more powerful with only very simple modifications:
  1. Draw the parabolic shape on the base so that the focal point is at the edge of the wood. Remember to mark the left-right location of the focal point
  2. Shape the metal so it follows the parabola on the base. It may be helpful to draw a parabola on a top-piece as well to make sure the metal stays the same shape all the way up.
  3. Position the router so the ACTIVE antenna is at the focal point (this is the one next to the reset button for the 54G
  4. Be sure to cover the router on all sides to keep it from getting filled with sand in windstorms
A more challenging, but also more effective design might be parabolic in both the horizontal and vertical direction to concentrate energy more efficiently. Hopefully we'll see some creative ideas for this in the future along with modified feed elements and tools for repeatable manufacturing...

Thursday, March 25, 2010

Fabfi hackathon - Complete!

Side Note: It's official, FabFi is happening faster than I can blog it out. The last two weeks managed to coalesce interviews for an upcoming Herald article, the Hackathon, and H&R installing a pile of new links. I'll be putting up a post-a-day until I catch up. Here goes post #1:


The goal of FabFi Hackathon 1 was to try to bring the FabFi architecture closer to the ethos of "do more with less". The plan was to look at the system as it exists now, identify what could be improved or repaired, and spend a weekend putting our heads together finding solutions. The following a a summary of what went on, which I will break out into more detailed technical posts over the coming weeks, pushing out what we have and soliciting advice. FABFI NEEDS MORE DEVELOPERS. If you want to help, email us (fabfi [at] fabfolk [dot] com)

A big focus of the weekend was design for local materials in Jalalabad. A major component of the hackathon's success was the participation of Jalalabad users who went out into the city and took pictures of all sorts of raw materials that were cheap and easy to come by, including metals,


plastics,


and different types of wood,



for us to consider when updating RF reflector designs. Our pal Kenny, who developed the original version of the current FabFi reflector, will be back on the case over the next month or so leading a global team to create a new reflector that's cheaper, more powerful and easier to make! In the meantime, Jesse got on the case of characterizing and improving my, as yet untested, rubber-ducky patch antenna feed hack (related post to come).

The real star of the weekend, however, was the ASUS WL-520GU. Now we all love the 54GL. It's a workhorse; it's reliable; and it's already been hacked every which way so you don't have to debug code. Sadly, the 54G will not be around much longer and it's already very difficult to come-by in the middle east. Enter ASUS--smaller, cheaper, comes with USB


and, as the photo above proves, available in Jalalabad at the local DigiTech.

Having just gotten our hands on a crate of 520GUs on Friday, the weekend was open-season for hardware hacks. Kerry wasted no time wiring up the console interface, while Jesse broke out the spectrum analyzer and set about characterizing the radio properties. by Monday we had a working FabFi FW image and a partially functional USB interface, and Jesse was convinced that this box would have as good or better wifi properties than the 54GL. Hameed will be beta testing the new offering and we hope to have a complete package with instructions for the device in a week or so.


In between firmware builds there was also a fair amount of thinking about configuration. The current fabfi infrastructure asks users to select a node number and a channel. While the installers of fabfis all know the overall system and each other, this works just fine, but knowing all the installers doesn't scale to thousands or tens of thousands of nodes. At that level, the network needs to manage itself. We didn't get much farther than a whiteboard on this front, but the ideas are now on the table.



Related to the autoconfiguration thought process, we also installed a local timeserver in Jalalabad and discussed better ways to log usage data. Conclusion: easy + "secure" + reliable don't all fit in the same sentence. Expect this to be a detail post in the coming week.

That's all for now. More to come tomorrow, and the next day, and the next day...

Thursday, March 4, 2010

Holy Crap we got /.'ed!!


Well, boingboing'ed to be precise.

...and Gizmodo'ed

...and freerang'ed

...and futurismic'ed

...and then apparently I got on Dutch TV (though I haven't seen it yet)

...and then the web site crashed from all the traffic. Go web 2.0! Jalalabad on the world stage! Cool huh?

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Nasty bug, oops!

Yep, fabfi is officially responsible for the net at my house being terrible for about three months... One stray character in the script that checks the WAN for a gateway results in constant resetting of the network when there is no statically entered gateway (and I think router needed to boot with the gateway entered...). Fortunately, dumb luck kept this from affecting the Jalalabad network uplink. We should get around to writing an auto-updater one of these days...

Bug is now fixed (yay). you can fix any 2.1 router by downloading and running the update script HERE. This will take you from 2.1 to the new current version: 2.1.1. For those of you who still need to get from 2.0 -> 2.1 use this updater before you use the one above.

Monday, March 1, 2010

Meaningless Model Numbers

Why bother to give your product a model number if it doesn't mean anything?

TrendNet seems to have the answer, as their TEW-652BRP sports completely different internals from V1 to V2 and, of course, V2 is built with a Realtek chip that won't run OpenWRT. So much for the $33 option. Next up, the $35 (after rebate) ASUS WL-520GU with USB...