Byzantium Sprint 2
From HacDC Wiki
Summary: Build at least one long-haul link to bridge two meshes.
Planning meeting: Thu Mar 3 2011 after the bike maintenance class (done) Planning meeting #2: Wed Mar 16 2011 after the elements of computing class (doneish)
Sprint Date: Fri-Sun March 25-27 Inventory
Schedule
FRI: 8:00pm Pizza, sprint 1 recap, and prep (mostly ripping thing apart and some assembly) SAT:
- Noon Brunch and final assembly followed by bench tests and midrange tests depending on speed of success
- Dinner Time: Dinner outside the space. This must occur outside the space.
- 9:00pmish? Discussion and general planning for Sunday optionally followed by more testing/making
SUN:
- Noon Brunch prep for long distance tests followed by long distance tests
- Dinner Time: Dinner outside the space. This must occur outside the space.
- 9:00pmish? Discussion and planning for the next sprint
Stuff to bring (proposed)
- FMRS/GMRS radios that you wouldn't mind hacking.
- Childrens' walkie-talkies. User:Drwho knows where to buy cheap pairs of them locally.
- Webcams that are known to work with Linux. That's closer to black magick than computer science, so do your homework first (or on your smartphone while at the store). The feature to look for is called UVC though webcam boxes still might not mention it.
- Laser pointers (the more exotic the colors the better). Buy them when you find them. When you go looking for them you can never find them.
- Really bright LEDs
- Photocells, photoresistors, photodetectors.
- Microcontrollers. They may come in handy for modulating/demodulating signals.
- Hackable wireless access points. Here are some examples that might work.
- old headphones/headsets/stereo audio cables and phone cords for cutting up and making into modem to radio connectors
Radio
- radio shack/hardware store high bandwidth unlicensed spectrum
- Hacked FRS/GMRS radios
- Text messages over walkie-talkies.
- Forum post with some ideas.
- Pros:
- cheap
- longish range (35mi allegedly)
- Cons:
- Need an automated PTT switch or two radios per node
- Develop improvised antennae to improve signal quality, distance covered.
- anything + aluminium foil = bouncy bouncy for radio waves
The FCC has designated a number of channels in the 27 MHz band that can be used for signaling and radio control. They are unnumbered and in-between CB channels 1-13 (source)
Optical
- Modified Ronja-like
- with lasers
- with balloon targets
- with lasers and balloon targets
- with lasers and self-adhesive mirrored decals.
- All Electronics Magazine had a couple of articles on building lasercomm devices on the cheap. Somebody remind the Doctor to go through his magazine collection.
- How to make a simple laser communicator. (I do have this issue. Have bought parts to build a pair of transceivers. --The Doctor)
- Handbook of Optical Through-the-Air Communications is a good read on the basics of an LED-based hardware setup, though he's aiming at voice comms. (Elliot)
Inspiration
Homework
- read up on Ronja
- read up on FMRS/GMRS
- read up on and talk to the HacDC Spaceblimp team about soundcard modems: like this (also available via apt like so)
- Howto(go here last it's a bit short on soundmodem specific info)
- Notes on Soundmodem
- Soundmodem in the field.
- Read up on AX.25.
Goals (proposed)
- Optimize for hackability. Could your average geek build a few of these using junk around zir house and deploy them in an emergency situation?
- not a chance
- Determine the optimum speed in bits per second for a mesh-to-mesh link.
- very crazy slow (we didn't bother measuring it was so slow)
- Measure the bandwidth of a point-to-point long haul connection at a particular distance.
- again to slow to bother
- Determine the maximum practical distance for a long haul connection between two meshes in an urban environment.
- didn't get that far
- Mathematically describe the way to maximize throughput with a minimum number of nodes.
- didn't get that far
- Run an ssh session over whatever link is established.
- done
- Interact with a web page over whatever link is established.
- connection was too unstable to get this far
- Develop methods to minimize latency.
- tweak the source and transmitter volume A LOT until the it's perfect
- Determine the efficiency of the mesh routing protocol we settle on.
- didn't get this far
- How many active nodes per mesh can be reasonably supported before connectivity breaks down?
- to be determined
Apps running on Windbringer (laptop/node) to prove functionality
Lessons Learned
- "how hard can it be" ... oops :(
- very. soundmodem is finicky and creates unstable connections 20% packet loss at best 80-90% avg.
- Don't forget network latency of 35,500ms over a distance of eight feet.
- "What could possibly go wrong?" ... oops :(
Let's see how much of Project FabFi we can make use of!