Bricked Netgear Stora? Arduino to the rescue!

My latest attempt at getting offsite backups working for me in the most convenient manner possible involves scattering storage devices around at places I frequently visit such as relatives places, etc. I thought I'd re-purpose a Netgear Stora device I had lying about (P.S. Don't ever buy one of these if you value your privacy) by modding the firmware on it. Turns out, an arduino makes a great TTL serial adapter if you short the reset pin to GND. :) 

I'm also particularly proud of my ghetto MacGyver-like pin connectors. They were created with PVC tape rolled around the leg of a resistor and then cut into thirds and slipped over each pin to hold them in place. (Yes, I need to get myself some more electronics gear...)

Pin outs here in case anyone stumbles across this wanting to do something similar. :)

 

DataMule - My first Android app. :)

I've been toying with various backup solutions for months now. I've tried tahoe-lafs. I tried my own hacky scripts and before that I even had the audacious idea of writing my own P2P backup software from scratch, starting at the low-level RPC layer.. My current approach is to use duplicity and throw the files on Google's cloud storage. The biggest problem with this latest approach is that full backups of my 100GB of data take about 12.5 days of maxing out my ADSL uplink. QoS eases some of the frustrations trying to use the internet while this is happening but doesn't completely remove them.

So DataMule is going to be a simple Android app that includes an SFTP/SSH client and configuration for pairs of WIFI SSIDs.

When you come into range of your "source" SSID, the SD card partition on your phone gets filled up with data copied via SFTP from your source server (until full). When you come into range of your "destination" SSID, the process is reversed and data is copied to the destination machine via SFTP. To complete the data migration, rsync is kicked off on the destination host with flag to delete after copying. The rsync will connect directly back to the source and copy (from the source) to the new file. This will just kick off a file hash verification and either delete the file (if its OK) or fix it if its not (with hopefully minimal bandwidth).

A HDD at work, a HDD at my parents place and an Android app and I'm all set. So far I've got a skeleton app working but its very very rough.

More updates to come!

Hacking at heat-maps and Google Maps API

I've been hacking away at a map visualization that I'm surprised hasn't appeared elsewhere already - a heatmap that interpolates between sample points. 

Every other heat map I've come across approximates interpolation by rendering circles with fading alpha at sample points and relies on the density of points to achieve a smooth result.

Below is an early screenshot of a canvas-based heatmap overlay I'm writing that is built from the Delaunay triangulation of the underlying data points (that's quite a mouthful!). 

I'm using a scanline-based Gouraud shading algorithm to render the triangles to the canvas myself having tried and failed to get WebGL, SVG and CSS to do the job for me (none of these can draw triangles with three different coloured vertices with any serious speed).

Prices for 2BR units across Sydney's inner west.

If there is interest, I will clean up and release the code once I have it working reasonably well and post it somewhere. For now, I'm rethinking my choice of Gouraud shading because with under-sampled data like I have here, it gives some very ugly, sharp lines.

I'm currently using it to display property values but hopefully others can think up some more good uses for it. 

GNU SDR and EZCap

Another nerdy post. I seem to be getting worse! :P

My ezcap USB dongle (RTL1832U/E4000) arrived from dealextreme yesterday and it took a whole hour of tweaking settings and wikipedia browsing to go from fuzzy crackle to working (and I think I understand the basics of it) software defined radio FM decoding. I started with someone elses grc file (although I can't remember who's) and tweaked it until I got to this setup.

In the top FFT you can see the station I'm tuned to in the middle and two stations on either side (they seem to be spaced every 800khz apart in Sydney). The bottom shows the filtered signal for the station I'm tuned to.

An amateur radio expert would probably laugh at me as I arrived at these settings through nothing but a bit of a rough direction and a lot of sheer luck but it seems to sound pretty good! Now I need to think of a legitimate use for this. :)

An experiment in Van Emde Boas layouts

Given an arbitrarily large sorted, balanced binary tree of values, the obvious way to search for elements is binary search. In undergraduate classes I learned that a binary search requires log(n) operations and is thus as efficient as you can get without throwing additional storage space at the problem. One thing my lecturer didn't dive into though was the effect of CPU cache on this otherwise simple little log(n) algorithm.

How to do dirt-cheap, cloud-based, encrypted backups (Part 2)

In my previous post I describing the method I used to store data online, I referred to what I was doing as a "backup" but it would have probably been more accurate to call it a near-real-time off-site mirror. In this post, I describe the pitfalls of my previous system and describe my much-improved latest technique.

How to do dirt-cheap, cloud-based, encrypted backups (Part 1)

I've been dabbling on code with the final aim of building a peer-to-peer distributed filesystem for a while now and I seem to keep hitting diversions along the way. In an internal monologue somewhat along the lines of "What would MacGyver do?", the idea for this concoction of open-source software and cloud services was born. In about 20 minutes or so of messing about (assuming you're comfortable with linux), I'll explain how you too can sleep sounder at night for $0.125/GB/month.