personalize it

Sep 15

“In brightest day, in blackest night,
No evil shall escape my sight
Let those who worship evil’s might,
Beware my power… Green Lantern’s light!”

Sep 12

Aurora Led with Atmega 8

http://rookiepeng.blogspot.com/2011/09/aurora-led-with-atmega-8.html

This awesome idea comes from the the led artist: http://www.theledart.com/blog/
I made another version with the atmega 8 MCU and 70 LEDs. It is not so good as the upper one. I just made it for fun. So watch the video first, which is recorded by my SGS phone.



Hardware:

PCB x1
ATmega 8L x1
3528 full color LED x70
SI2301 P-Channel MOSFET x3
9013 NPN BJT x11
20K ADJ resistor x3
button x2
resistors and capacities

Environment:

Microsoft Windows 7
Fedora 15
Vim
AVR Studio 5
Altium Designer 10
SVN

If you want some detail information,  please email to: rookie.dev@gmail.com

Sep 10

A Bash Script to Create Multiple User Accounts in a Batch

http://rookiepeng.blogspot.com/2011/09/bash-script-to-create-multiple-users.html

There are a lot of introductions on the Internet about how to create multiple user accounts in a batch with “newusers” command. But in this way, there are some problems about the environment variables. The system will not initialize the “.bashrc” and the “.bash_proflie” files.

Here is anther way to create multiple user accounts with “useradd” command.

#!/bin/bash
password="123456"
for USER in $(cat example_userlist)
do
    useradd -m $USER
    echo -e "${password}\n${password}" | passwd $USER
done

The password of all the users is “123456”, it can be changed in the second line.

In this script, the “example_userlist” is a list of user names, the format of this file is like this:

user1
user2
user3
...

Enjoy!

Sep 08

E-T waveguide power divider

http://rookiepeng.blogspot.com/2011/09/e-t-waveguide-power-divider.html

This is a 2-way power divider I made, which is used in a broadband feed net of a horn antenna array. Firstly, a E-T junction (figure 1a) can equal to a transmission line model like figure 1b.The junction is inductive.Here we assume that the impedance of L1 is Z0. So the S11 of this structure is not very good. For a perfect power divider, the impedance of L2 and L3 must be 2Z0, at the same time, the junction must not be inductive nor capacitive.

Figure 1 normal E-T junction

For the impedance, we can reduce the height of the waveguide to increase the impedance, while we can add a step in the junction which is capacitive and it can neutralize the inductance. So the final structure of the E-T junction is like figure 2. Figure 3 shows the S11 of this structure, the cutoff frequency of the waveguide is about 10.5GHz.

Figure 2 broadband E-T junction

Figure 3 the S11 of the structure

Now the impedance of L2 and L3 is 2Z0. We can use the impedance conversion method to convert the impedance to Z0. In the figure 4, I use Chebyshev impedance conversion method. The length of each impedance transformation segment is λ/4. The S11 of this structure shown in figure 5.

Figure 4 2-way power divider with Chebyshev impedance conversion

Figure 5 the S11 of power divider with Chebyshev impedance conversion

Sep 01

new headphones, sennheiser px 100 ii