| SOLAR PROJECTS

Saturday, 18 February 2012

iCare Data Recovery - a program to recover deleted and formatted files from hard drives, sd cards, memory cards and USB Flash drives. It helps you to recover files from unreadable disk partition, if damaged boot sector or a virus attack.

The program includes 4 Restore Wizard:
• "Partition Recovery" to recover deleted partition
• "Deleted File Recovery" to recover deleted files, files from damaged partitions or corrupted boot sector, etc.
• "Deep Scan Recovery" for scanning and searching of both existing and deleted files that can be restored
• "Format Recovery" to restore files from hard drives, external drives, sd cards, USB Flash Drives

Data loss won't be your headache! As a comprehensive data recovery solution, iCare Data Recovery can easily recover files from wrong formatted drives, unexpectedly file deletion, raw drive or raw filesystem, virus attack, partition deleted, software crash etc. It can recover any deleted files like photos, documents, mp3, outlook file, presentations, and it also works with any type of storage media like hard drive, removable hard drive, digital camera sd card, usb drives, ipod, memory card etc.

"iCare Data Recovery Software combines simplicity of use with the most powerful file recovery software engine, which can search and find files&photos missed by other recovery software, together with a unique capability of "on-the-fly" data preview while the search is being conducted."

iCare Data Recovery Software
• Reformatted partition, memory card, camera card by accident?
• Corrupted MBR and cannot find your partition or USB not detected?
• Accidentally deleted partition?
• Drive became RAW?
• SHIFT+DELETE and need file recovery?
• Recover files from dynamic disk
• Data loss without a reason, Need recovery software?

Friday, 10 February 2012

D.C CIRCUIT ANALYSIS

A network of passive elements and sources is a circuit.
Analysis: To determine currents or voltages in various elements (effects) due to various sources (cause).

**Figure 4.1:**
$\includegraphics[width=3.0in]{lec3figs/1.eps}$

In circuit 4.1 all the time.
Expected that all current (voltage) in (across) the elements is constant.
Inductor:

$\displaystyle v=L\frac{di}{dt}$

(4.1)

$\frac{di}{dt}=0$ implies constant.
Hence
Inductors act as a short cicuit for DC inputs. This would not be the case if I put a switch across a source.
Capacitor:

$\displaystyle i=C\frac{dv}{dt}$

(4.2)

as $\frac{dv}{dt}=0$ (expected), .
Thus capacitor acts as open circuit for DC analysis.

**Figure 4.2:**
$\includegraphics[width=3.0in]{lec3figs/2.eps}$

The resultant circuit will be as shown in Fig.4.2.
Analysis: To find currents in all branches, voltage across all branches.
We can use Kirchoff's law (voltage and current). For as many independent equations as number of unknown variables.
Solve the simultaneous equations, and get the result.
$V_{ab}=$ Voltage drop from 'a' to 'b'. Therefore, $V_{ab} = - V_{ba}$
$I_{ab}=$ Current in branch ab in the direction from 'a' to 'b'. Here $I_{ab} = - I_{ba}$ .
Hence:

$\displaystyle V_{fa}=-v$
$\displaystyle V_{ab}=I_{ab}\times 1=I_{ab}$
$\displaystyle V_{be}=I_{be}2$
$\displaystyle V_{ef}=I_{ef}1$
$\displaystyle V_{bc}=I_{bc}1$
$\displaystyle V_{cd}=I_{cd}2$
$\displaystyle V_{de}=I_{de}3$
$\displaystyle V_{ab}+V_{be}+V_{ef}=v$
$\displaystyle I_{fa}=I_{ab}$
$\displaystyle I_{ef}=I_{fa}$
$\displaystyle I_{bc}=I_{cd}$
$\displaystyle I_{cd}=I_{de}$
$\displaystyle V_{ab}+V_{bc}+V_{cd}+V_{de}+V_{ef}=v$
$\displaystyle I_{bc}+I_{be}=I_{ab}$

Note: In a circuit with nodes, the number of branches will alwasy be , where are maximum number of independent closed paths possible in the circuit.
Hence, we can always form equations using Ohm's law, equations using KCL, equations using KVL. Hence in total equations can be formed, which are sufficient to solve for variables (voltage and current in each branch).
Can we simplify the situation? Loop currents method: We do away with branch currents and define loop currents. The branch currents can be written in terms of loop currents once all the loop currents passing through the branch and their directions are known. The branch voltages can always be written using Ohm's law and branch current written in terms of loop currents. So now our objective is to find loop currents. For this we choose maximum number of independent loops (Fig.4.3) and apply KVL in them.

**Figure 4.3:**
$\includegraphics[width=3.0in]{lec3figs/3.eps}$

If and are known, voltages across all elements can be found.
Make two independent equations:
For loop abef

$\displaystyle v-i_1\times 1 -(i_1-i_2)\times 2 -i_1\times 1 =0$			(4.3)
$\displaystyle v=i_1(1+2+1)-2i_2$			(4.4)

For loop bcde:

$\displaystyle -(i_2-i_1)2-1i_2 - 2i_2 -3i_3=0$			(4.5)
$\displaystyle 0=-2i_2 + i_2(2+1+2+3)$			(4.6)

Use any technique to solve these (such as using matrices). We get:

$\displaystyle i_1=\frac{2}{7}\;Amperes$			(4.7)
$\displaystyle i_2=\frac{2}{7}\; Amperes$			(4.8)

Nodal Voltage Method

**Figure 4.4:** Nodal Voltage method
$\includegraphics[width=3.0in]{lec3figs/4.eps}$

Considering Fig.4.4.
Independent Nodes: One of the nodes in circuit need to be considered as reference node. Hence its node potential is zero. For other nodes, nodal voltage is potential differetial w.r.t. to reference node. The nodes are called independent nodes. In general for node network, nodes will be independent.
At node b: .
Similarly, other equations are:

$\displaystyle \frac{E_a-E_b}{1}-\frac{E_c-E_b}{1}-\frac{E_b}{2}=0$			(4.9)
$\displaystyle \frac{E_a-E_b}{1}=i_{fa}$			(4.10)
$\displaystyle E_a=E_f+v$			(4.11)
$\displaystyle \frac{-E_f}{1}=i_{fa}$			(4.12)
$\displaystyle \frac{E_c-E_b}{1}=\frac{E_d-E_c}{2}$			(4.13)
$\displaystyle \frac{-E_d}{3}=\frac{E_d-E_c}{2}$			(4.14)

These are six equations, in six unknowns. Thus can be solved for a unique solution. One can make a supernode and use KCL combining the nodes nodes a and f. We also make extra equations for potential difference between two nodes.
With supernode, no. of equations is equal to no. of independent nodes whose voltage w.r.t. reference needs to be determined. Current Sources in Loop Current Analysis

**Figure 4.5:** Current sources in Loop current analysis
$\includegraphics[width=3.0in]{lec3figs/5.eps}$

Using KVL for loop 1 in Fig.4.5:

$\displaystyle 5-i_1-v_{bg}-(i_1-i_2)1-i_13=0$

(4.15)

The other equations are:

$\displaystyle i_1-i_2=2$

(4.16)

$\displaystyle v_{bg}-i_22-i_21-i_22-(i_2-i_1)=0$

(4.17)

The first and the third equation can be combined for taking care of $V_{bg}$ . This can be done by making superloop for writing KVL.
Graph
For analysing circuits efficiently.
Loop current method
One can form a spanning tree from graph such that current sources are in links (Those elements which do not form part of the tree). Each link when added to the tree gives a loop. All voltage sources should be kept in branches of tree. For example, refer to the following two figures (Fig.4.6 , Fig.4.7)

**Figure 4.6:** Loop Current method
$\includegraphics[width=3.0in]{lec3figs/6.eps}$

**Figure 4.7:** Loop current method
$\includegraphics[width=3.0in]{lec3figs/7.eps}$

Node voltages

**Figure 4.8:** Node Voltage method
$\includegraphics[width=3.0in]{lec3figs/8.eps}$

In the above figure, $V_{af}=2V$ . There are five unknown node voltages in the above circuit, namely, $V_{ab}$ , $V_{fe}$ , $V_{bc}$ , $V_{cd}$ and $V_{ge}$ . Correspondingly, we have five equations. Note that we can merge into one supernode

$\displaystyle V_{ab}+V_{fe}/3=0$
$\displaystyle V_{ab}-V_{bc}/2 + 2=0$
$\displaystyle V_{bc}/2-V_{cd}=0$
$\displaystyle V_{cd}-V_{de}/2=0$
$\displaystyle V_{ge}+2=0$