Archive for

March, 2014

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Proto boards and microcontrollers – an overview

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MAKE magazine has a nice write-up of several of the popular micro controllers, prototyping and hobby boards out there. 36 of them in total. Of course, that covers only a fraction of all the brands, models and variations. That list runs much much longer.

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Hubsan X4 H107C Quadcopter

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Lately I’ve had great fun with the miniature quadcopter Hubsan X4 H107C. I’ve already lost the first I got, and the second was this one from Deal Extreme. Right now, they all seems to be sold out, but there are hundreds of other brands to choose from in all price ranges. Starting with this single axis “flying saucer” at only $15. The first quadcopters start at about $30, and most of them seem to be copies of the Hubsan. They have a Walkera with GPS hold starting at $333, all the way up to the 6 channel version which supports First Person View (FPV) glasses.

YZ-L Mini 2-CH LED Radio Control R/C Flying SaucerHubsan X4 H107C 2.4G 4CH R/C Quadcopter w/ 0.3MP CameraWalkera QR X350 6-CH R/C Quadcopter w/ GPS / DEVO F7 5.8G FPV Transmitter RTFWalkera E002 FPV First Person View Goggle Glasses Support DEVO F4/F7

For the Hubsan X4, there are a few extras to get. First of all, the propellers will break, so make sure to get plenty of replacements. Also be aware that they are directional, so there are two of each kind in a bag. A few extra batteries are nice, since a single one will only give about 8 minutes of light time with almost an hour charge time. So to avoid spending hours charging them, some extra chargers also come in handy. Finally, a micro SD card is required for the camera; 2 GB, or even only 1 GB is plenty.

And up and up it goes! Until the wind takes it away, it lands on an inaccessible rooftop and you’ll have to get another one. :-)

Hubsan H107-A02 Replacement BladesHubsan H107C-A24 3.7V 380mAh Li-po Battery for H301CHubsan R/C Spare Parts H107-A06 USB Charger for H107 / H107L

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Key mappings in Zsh

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Z-Shell is a powerful alternative to Bash, but some of the details can take time to get use to, and some things just have to be changed. For example, the key binding for cursor and other special keys. Using CTRL + arrow keys to skip words might give funny characters like “;5D” and “;5C” instead. As pointed out by Luke Wilde, these keys have to be set up manually. In my case, I had to include the semi-colon in the bindkey command as well.

These should go in ~/.zshrc.

bindkey ';5D' emacs-backward-word
bindkey ';5C' emacs-forward-word
 
export WORDCHARS=''

Only funny thing about setting it up like that, is that if the actual character sequence “;5D” is pasted into the terminal, it will be taken as if the CTRL+LEFT key was pressed. I’m not aware of a work-around for that.

The Zsh wiki lists a few other possible key bindings, including for the Home and End keys:

bindkey "${terminfo[khome]}" beginning-of-line
bindkey "${terminfo[kend]}" end-of-line

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Multiplexed SSH sessions for quicker connection

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If you need to open multiple SSH connections to the same host, it can get tedious to re-authenticate for every one. And even with public key authentication and no password, the extra channel eats a bit of bandwidth. The solution is multiplexed SSH sessions: Authenticate once, and the following connections to the same host goes over the same session. It’s dead easy to set up:

In your ~/.ssh/config file add the following lines. (Make sure that file has user permissions only, i.e. 600).

Host *
   ControlMaster auto
   ControlPath ~/.ssh/master-%r@%h:%p

It takes effect immediately. SSH twice to the same host to verify.

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