Simple Darkness Sensing LED

Evil Mad Scientists have create cool and simple Darkness Sensing LED ever. It's only need few component: a CR2032 lithium coin cell (3 V). LED, an LTR-4206E phototransistor, a 2N3904 transistor, and a 1 k resistor. You can choose it for your first project during learning electronic.

"When light falls on the phototransistor, it begins to conduct up to about 1.5 mA, which pulls down the voltage at the lower side of the resistor by 1.5 V, turning off the transistor, which turns off the LED. When it’s dark, the transistor is able to conduct about 15 mA through the LED. So, the circuit uses only about 1/10 as much current while the LED is off. One thing to note about this circuit: We’re using a red LED. That’s because the voltage drop across the transistor allows less than the full 3 V across the LED. The full three volts is really only marginal for driving blue LEDs anyway, so two-point-something really doesn’t cut it."

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Simple RS 232 Level Converter

When you need connect your Microcontroller Project to COM port in PC you need RS 232 converter. There are many chip to solve the problem like MAX232, DS275 etc. But if you need simple and chep for RS 232 converter, i though this circuit will be usefull for you. The design made by Wichit Sirichote.

"A circuit diagram shown above was used two small signal transistor, NPN and PNP transistors. Dash line separate transmitter and receiver circuit. For those who need only transmitter circuit can use above circuit (and GND (5) signal ). Technically the RS232C is -3V to -12V for logic '1' and +3V to +12V for logic '0'. The transmitter circuit uses PNP transistor, BC557. While in mark state the TxD signal is logic '1', Q1 turns off. TxD (pin3) then provides -9V (depends on what converter chip being used for COM1, say) to RxD (pin2). For space state, TxD control signal then becomes logic '0', which turns on Q1, the approx. +5V is then fed to RxD (pin2). With this method, while sending data has being made, TxD (pin3) must stable at -9V, say"

There also some modification from above circuit. For more detail you can download here.
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How to Install XBMC MediaPlayer in Ubuntu 10.04 (Lucid Lynx)

XBMC is an award-winning free and open source (GPL) software media player and entertainment hub for digital media. XBMC is available for Linux, OSX, Windows, and the original Xbox.
Currently XBMC can be used to play almost all popular audio and video formats around. It was designed for network playback, so you can stream your multimedia from anywhere in the house or directly from the internet using practically any protocol available.

How to Install XBMC MediaPlayer in Ubuntu 10.04

sudo add-apt-repository ppa:team-xbmc/ppa
sudo apt-get update
sudo apt-get install xbmc-standalone