At Isai Ambalam

For the first few weeks I decided to teach and learn with the 5th graders at Isai Ambalam middle school, at class we worked out many logic puzzles. The class was at the stage of working out multiplication and division. Speed,distance,time and interrelating each other to form stories of multiplication and division were introduced…

e.g.: if a car travels at a speed of 25 km/hr, what will be the distance covered by the car in 4 hours?

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The students multiplied and came up with a solution, by saying that the car would cover a distance of 100kms. The same story was made into division

e.g.: if a car covers 100km in 4hours, what is the speed of the car? The speed of the car is 25km/hr

Screenshot from 2015-04-11 15:04:11the students were able to make out the stories, as we got into creating many different stories I started to realize that not all students did understand what they were making up, some got confused or did not understand the units..

I asked the students how far was their home from school, well there were many loud answers, but each answer terminated with a unit of distance( the lesson learn ‘t was to never ask a general questions to the whole class, or else expect a chorus answer if you don’t want that to happen, be more specific and select a random child to question) . They all knew that time was in hours, but the units of speed and distance always seemed to confuse them until they came to realize that speed is the amount of distance covered over a certain period of time….

the real reason was that the majority of the students did not understand English very well, being bilingual is very very important. But once the conversation starts in Tamil( mother tongue) its easy to forget the conscious of switching back to English…

by the time these few weeks passed the relation with the class grew stronger, I came to realize that there were some four students who seriously did not know what they were doing in mathematics class… every class has a few slow learners, but having students who could not multiply, or even added by using their fingers seemed a little bit odd. I decided to take into consideration these four members of the classroom.

The five of us would sit together and start to solve some multiplication problems, after a while they seemed to get a handle of the multiplication… but the problem showed up in the addition part after multiplying two, two digit numbers… simple additions required finger counting, they could not do mental calculations. If asked what is five plus six they would take five fingers and then start to count six fingers, to see that number 1 was left after adding five plus five and the answer was 11 was not that obvious.

DSC_0523To create a change the abacus was introduced and still it was a little hard to see the fives, as the whole ten beads were the same colour. Now the abacus was taken apart and every five beads were altered so as to see the simple pattern of fives. After this, the pattern was seen that when one adds five to seven the remaining number of beads is two and the answer is twelve. To have broken the pattern of finger calculation which they were stuck with for all these years felt awesomely superb. But after a few days with the abacus rigorous training was difficult and the student seemed to be getting a littler tired of beads counting….

that is when introducing scratch programming seemed to ignite a little spark, as a team we came together and built a small script that added two digit numbers. The children were so excited and eager to solve the sums in scratch than before with the abacus. Now doing mental calculations seemed to easier than before.

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Scratch stories with Udavi 8th graders

Scratch stories with Udavi 8th graders

The 8th graders at Udavi had made stories on the theme ‘ if i had wings ‘ , they were wanting to depict their stories with scratch. The time offered was four English class hours on that week, and so the fun began… on the first day all the students had worked through an idea of what they wanted to depict with scratch programming, and when asked to pair up as a team and do their work, the usual boy-boy and girl -girl teams appeared. To make things more collaborative and interesting we mixed up the pairs into boy – girl.., asked on what aspects , criteria they were willing to do evaluate the work. They came up with the following





-Using Proper Language



The class was just so amazing, all the children were totally focused on their work as a team there were no cross talks between teams.

DSC_0512The students used the Internet to get their characters and backgrounds. Gimp was introduced to them as and editing tool.



DSC_0513On the 2nd and 3rd day the children continued working with their script. They were also engaged in giving feedback with the mentioned aspects. Towards the end of the last assigned day all the projects were decided to be merged as to make a single video. The students amongst themselves coordinated and went along other teams that were still engaged in their scripting, and started to explain the process of merging files.

Incremental Backup for Ubuntu

The command :

tar -cvfz -X excludeList -g 20150407.snar 20150407-full.tar.gz ~

tar-cvfz – creates all the files.

-X excludeList – creates a folder where one can exclude the files that need not be backed up.

-g .snar – this is the command used for incremental backup.

.tar.gz ~ – create .gz files which can be extracted later

  • At first do a full blind backup of all your files.
  • Then for the next backup, create a new .snar file and copy the old .snar to the new one.

Calculating ESL of a Capacitor

Impedance of Various 100μF Capacitors :


  • The figure tells us that the impedance of a capacitor will decrease monotonically as frequency is increased.

  • In actual practice, the ESR causes the impedance plot to flatten out.

  • As we continue up in frequency, the impedance will start to rise due to the ESL of the capacitor.

  • The location and width of the “knee” will vary with capacitor construction, dielectric and value.

  • This is why we often see larger value capacitors paralleled with smaller values. The smaller value capacitor will typically have lower ESL and continue to “look” like a capacitor higher in frequency.

  • This extends the overall performance of the parallel combination over a wider frequency range.


Reference : From Analog Devices Tutorial

Frequency Characteristics of a 0.1 uf Capacitor :


The impedance matches with ESR at around at around 2 Mhz.

ESL Analysis :

Frequency = 20 Mhz

Capacitance = 0.1 uF

From the frequency equation , ESL = 0.63 nH

 Frequency Characteristics of a 1 uf Capacitor :

The impedance matches with ESR at around at around 8 Mhz.

ESL Analysis :

The impedance matches with ESR at around at around 8 Mhz.

Frequency = 8 Mhz

Capacitance = 1 uF

From the frequency equation , ESL = 0.39 nH


The impedance matches with ESR at around at around 2 Mhz.

ESL Analysis :

Frequency = 2 Mhz

Capacitance = 10 uF

From the frequency equation , ESL = 0.63 nH

Frequency Characteristics of a 10uf Capacitor :


The impedance matches with ESR at around at around 2 Mhz.

ESL Analysis :

Frequency = 2 Mhz

Capacitance = 10 uF

From the frequency equation , ESL = 0.63 nH

Capacitor Graph Reference : Datasheets from Digikey



Lets analysis the following circuit.


This circuit consist of two nodes named as v1 & v2
Consider the input voltage is vin .
Lets say the current ‘i’ is passing through the node v2 .
Then the voltage at the node v2 is given by
Voltage at the node V1 is given by
Then the input voltage vin is given by
Substituting the value of V1 in equation 3 we get,
09    (Equation 4)

Then the current ‘i’ passing through the node V1 is,
76    (Equation 5)

The transfer function (by substituting the value of ‘i’ in equations 1 & 2)

Circuit Analysis



Assume a current ‘i’ flows in a particular direction.

The voltages at the nodes have been named as vin, v1,v2

At node v2 :


At node v1 :


Through SL1 :


At vin :


v1 and v2 in terms of vin :



Circuit Analysis

Circuit Analysis pdf


let us take the above circuit into consideration, with three nodes namely:


and i is the current passing through them.

1. Considering node v2 :


2. Now at node v1 :


3. To determine vin :


4. The current i can written as :


5. v1 and v2 in terms of vin





Stewardship for New Emergence

To me, workshop simply means learning new technologies and technical tools (as I only attended technical workshops) . Stewardship for a New Emergence (by Monica Sharma) was totally new for me & gave different experience.

Sometimes, I failed to listen others due to some background conversations in my head. These conversations created misunderstandings in communication. But, I never thought of how I can let it go. I didn’t even noticed this. But this workshop gave a link to think about that. Yes, the primary steps to solve the problem is to start noticing them and making a conscious choice of let it go. 

Before attending the workshop, I thought someone will come & give lectures. But what I experienced was something higher . They taught the tools as well as created the environment to practice them with a peer(co participant).

Most case, I used to avoid pin pointing the mistakes in one’s work though it is helpful for them to grow. Because I believed in that i am not good enough to give feedback.  This workshop gave some procedure to give feedback for others to grow. It also helped me to see commitments behind the complaints of others and I learnt that the growth happens beyond the comfort zone.

World is extraordinary and filled with many opportunities. Its all about our perspective of seeing the world. So stand up & open your window to get there where you wished to reach in spite of difficulties that may surround you. And remember, confusion & mistakes are birth  place for knowledge & perfection. In the world no one has the power to make me to feel bad without my permission. If I bounded with emotion, it will reduce my energy and can not allow me to further action.” These are the few things I absorbed intensely at workshop & planning to practice in my life.

Most of the things which I learnt in the workshop are not completely new to me or to anyone. But the thing is it stimulates me to think about it consciously which I never did in my past.


Powering up an LED

PoweringUpLED pdf

Powering up an LED ; A useful tool to determine the value of resistors to be used in the circuit.

V = I × R (Ohm’s law)

supply voltage = 5V

resistor used = 2 x 33ohm resistor connected in parallel = 16.5 ohm

to determine current ; I = V / R

5 / 16.5 = 300mA

(Power supply voltage − LED voltage) / current (in amps) = desired resistor value (in ohms)

To calculate the amount of power that the resistor will dissipate;

Power Rule: P = (I × V ) W
If a current I flows through through a given element in your circuit, losing voltage V in the process, then the power dissipated by that circuit element is the product of that current and voltage: P = I × V.

led1 led3


Speede V.2

SpeeDe V.1 -pdf

upgraded features ;

– 12 v battery

– improved LDR sensitivity

changes made ;

– 12 v battery

On Speede v.1 we used 2x 9v batteries, one for driving the arduino board and another for powering the laser. This did not suit the device as it kept on draining up the batteries. Which made us upgraded the battery source to a 12 v rechargeable battery, but the laser and the arduino kit could only handle 9v supply. This made us connect an IC 7809 from the battery source and then supply the components ( ic 7809 simply burns the excess voltage i.e.3 v and provides a supply of 9v as an output)

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– improved LDR sensitivity

The LDR’s sensing the laser were affected by external light sources, this compromised Speede’s ability to work in a brighter environment. In order to eliminate this factor, two pvc tubes were fitted around each LDR.

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