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Showing posts from August, 2013

How to Fix "Virtual Router" 0.9 and Above - "Virtual Router Can't Be Started"

Aside from electronics and communications (physical layer), we've also had network fundamentals taught in our curriculum (through advanced). I've heard of this free software called Virtual Router that allows you to turn your computer into a router per se. Strictly speaking, by definition of a router, it doesn't. But it looks like it serves the purpose of a wireless router configured for 802.11 services, so that will suffice. And its free, so I gave it a shot. I've managed to turn a broadband connection from a USB connector (SMART, that is) into a wi-fi hotspot. It offers WPA2-PSK encryption and a view-able list of devices connected. However, a problem occured after some time using it. That is, when I click on the Start Virtual Router button, a window would appear saying that "Virtual Router Can't Be Started". Some suggest to simply restart the program, or wait some time. Sometimes this won't work, and not for everyone. Why? Sometimes, the targets…

Proposed Solutions to Doomsday Asteroids

The risk of a collision course with asteroids has fueled the imagination of countless writers and movie producers. One lump of rock (ice or something) more than 1 kilometer in size strays away from the asteroid belt or outer solar system and goes on a collision course with Earth. The asteroid upon entry will heat up the Earth's atmosphere and end all life, sharing the same fate as the dinosaurs. Fortunately, we now have enough knowhow to meddle with cosmic affairs, such as landing probes and rovers on extraterrestrial territories. But is it enough to stop a 1-kilometer-big bullet from hitting its 6400-kilometer-big target? I don't know. Watch National Geographic, they have a program specifically tailored to this. But that doesn't mean you shouldn't read on.

     Below are some solutions given by external sources with the details explained from my perspective:

A.) Shooting Lasers from the Moon

Effectiveness: 1/10

Simplicity: 2/10

Feasibility: 0/10


Fast Facts: Current Mirrors

The current mirror is very popular in IC design. But what does it do? As the name implies, it simply tries to provide a stable current source by "mirroring" the current of a reference branch. (Remember that current sources when loaded still provide the same amount of current, the voltage varying consequently). The current mirror is constructed by shorting a collector and 2 bases of 2 BJTs and a drain and 2 gates of 2 MOS.

Below is a futile attempt in simulation [back when I was still a college amateur].

In order to understand how the transistors provide equal constant currents, let us take the example below.

     Above are 2 2N2222 NPN transistors functioning as a current mirror. Q2 has its collector shorted with the base. The 2 resistors are ohmic, so we can assume Ohm's law to be valid over that branch. The current supplied is 5 mA and 6.667 mA(initially) to Q2 and Q1 respectively. The bipolar junction transistor is a current controlled device. Thus, if the col…