Month: February 2014

I've been had!

Posted in Electronics, Reverse Engineering - February 12, 2014 - 0 Comment

I got a “5600mAh” power bank from Aliexpress. It’s an electronic item direct from China at low, low prices, so I assumed it was going to not measure up in some way or other, but until I got it, I didn’t know how.

Overall, the build quality isn’t bad. The case is molded plastic, and snaps together. It’s nice looking and feels solid. The power management PCB in it seems to have good quality solder joints. Not too shabby, and I don’t expect it to catch fire or anything.

The batteries, on the other hand, are where it falls down. The device has two cells in it, 18650 size, 1200mAh each (if their labels are to be believed). They are in parallel, which gets me a total of 2400mAh. That’s slightly more than half of the advertised capacity. Since 5600 isn’t an even multiple of 1200, there’s no way they could get 5600mAh using these batteries, even if they did want a product that could live up to their claims.

For ~$9, I don’t think it’s worth making a fuss over, but now I know what to expect from this device.

"Weaponized" Quadcopters

Posted in Bad Ideas, Lasers, Robotics, Security - February 4, 2014 - 0 Comment

For a long time, I’ve been thinking it would be possible to strap a small explosively-formed penetrator (EFP) to a quadcopter. Then you feed the GPS coordinates of your enemy’s apartment or office into the on-board navigation system, and the quadcopter flies over to their place and fires a hypersonic slug of copper through their window.

Leaving aside the ethical concerns, there are a couple of issues with this. The main one for asymmetric warfare enthusiasts is that it destroys your quadcopter and leaves bits of it at the scene, which wastes resources and gives clues to whoever you were trying to shoot.

Then I saw this little post over at Hackaday. If you put a high wattage diode laser on a quadcopter, you can have it set fire to things. It could probably shoot through a glass window and set fire to things on the inside of the window. Once the place is nicely in flames, you just fly the ‘copter away again, leaving no trace.

Un-ubuntuing Ubuntu…

Posted in Linux - February 3, 2014 - 0 Comment

..post one of several million, no doubt. Ubuntu is pretty good, but persists in making what I’d regard as irritating desktop usability blunders. One of them is the use of “overlay scrollbars” which are scrollbars that are mostly hidden until you mouse over them. I found this annoying, but whatever, I can deal. It even more or less works, most of the time.

However, it breaks Inkscape. Inkscape’s color picker is a long strip of color patches, which you can click to select stroke and fill colors for drawings. The color picker has a scrollbar. If overlay scrollbars are on, then the entire area of the color picker ends up being the mouse-over area for the overlay scrollbar, so you can’t pick colors.

The fix is to issue the command “gsettings set com.canonical.desktop.interface scrollbar-mode normal” from the command line.

Useful mencoder invocation

Posted in Linux, Scripting - February 3, 2014 - 0 Comment

mencoder -nosound mf://*.jpg -mf w=1280:h=800:type=jpg:fps=30 -ovc lavc -lavcopts vcodec=mpeg4:vbitrate=2400:mbd=2:keyint=132:v4mv:vqmin=3:lumi_mask=0.07:dark_mask=0.2:mpeg_quant:scplx_mask=0.1:tcplx_mask=0.1:naq -o output_filename.avi

Turns all the JPEG files in the directory you are currently in into a nice quality MPEG-4/AVI file. The width and height in the options after -mf should be changed to match the images. This command line also works for PNG files if you replace both instances of “jpg” with “png”.