Monthly Archives: September 2015

Creating a Spice Model from a .subckt file

The following video demonstrates on how to create a spice model of a component, from a .subckt file which can be acquired from the retailer.

following is a spice model file for a bridge rectifier ; mb6s

data sheet : MB6S_MCC

– Open LtSpice

– Browse for the file and open

– Once opened right click .subckt and create model and design your circuit.

-Ref :

Op-Amp positive feedback design

The following circuit has a voltage source that operates between 3V and 5V and is connected to the Op Amp’s positive input, across a resistor divider R2 and R1 at the node Va. The simulation is run for 200m secs.


The design is as following: applying super position










Following is the Spice file :  opamp_gnd

Video :Positive Feedback







Science Technology Engineering and Mathematics (STEM):

STEM Land:

STEM Land  is a place for ‘Learning’ which we are creating in Udavi school. The vision behind the STEM is learning based on Concepts, practical observation & abstraction. In short “Mediocrity to Excellence“.

It has large variety of materials ( Robot, Physics based materials & kits, Demonstration models, Electronic components & tools, variety of Measurement Equipments, Montessori & Jodo Gyan materials, Strategy games, Puzzles and Books). So we can engage all the students based on their capacity level without letting them feel overburdened  or bored. Most of the students get enthusiastic and become active learners when they get into a new environment ( where the usual text books are absent). So it is added advantage of STEM.







This three students (7th Grade) have assembled the Robot parts (nearly 300 small pieces). They also programmed the Robot for a challenge I set for them (with guidance). Here they learnt how to be systematic (while assembling the parts of Robot). And became programmers when they started to  program the Robot.








This student is an example of perseverance. Many people gave up when they were trying to solve this square puzzle (including me).  One of the reasons was, we got bored. But he pursued  till he reach it. Our curriculum needs this type of activities to empower students to use their creativity to solve problems, ask questions and continually learn.


Students  need to be challenged. At the same time not  be bored. I hope strategy games are one of them which satisfy this condition.  And this made them think and observe keenly without supervision.

LtSpice – Introduction

LTspice IV is a high performance SPICE simulator, schematic capture and waveform viewer with enhancements and models.

The simulator software can be downloaded from the following link:

The following is a circuit on how to use a switch ” .model ” in simulations, it has been created for a RC circuit.sw

As seen these switches are not a physical model, they require a initial voltage to start to act as one.

20150820_switch_RC is the simulation file for the given circuit, can be seen by installing LtSpice.



Every switch has some instance of resistance when on or off;
Ron = 1            ‘ the resistance when the switch is turned on.’
Roff = 10meg   ‘ the resistance when the switch is turned off.’
Vt    = 0.1         ‘ the instance when the switch turns on’

Classical way to solve the RC filter in time domain :

RC filter classical time domain way


Area with GeoBoards

I was doing shapes( squares, rectangles and triangle) with 4th and 5th grade children. Then I thought of introducing areas also to them. Doing areas with formulas would be a little difficult for them as they are not yet fully comfortable with multiplication. Then I got to know about GeoBoards. Geoboard is material where children can make all kinds of different shapes they want using rubber bands. It has 64 little squares. Once they make a square or rectangle, all they need to do is to count the number of squares present inside the shape they made. For triangles, we needed to make a rectangle and draw a diagonal so that it makes two triangles inside the rectangle. Area of one triangle is then half the area of the rectangle. As they got more used to it, they didn’t count the little squares anymore and instead they counted the rows and columns to find out the area. Children found it pretty interesting and they could get it quite easily. With material in hand the class is never boring!