Category Archives: Circuits & Simulations

designing 4-bit microprocessor using magic tool

I started designing 4-bit microprocessor in magic tool, it consists of three block:

  • 4-bit full adder
  • register to store an input data.
  • 4-xor gates and one carrier input is used to 2’s complement for subtraction

Inputs which are used in it :

  • two 4-bit data A and B
  • carrier input
  • clock



In this microprocessor, the adding operation is takes place when carrier input is 0, and the subtraction operation takes place when carrier input is 1. During subtraction, one’s complement block takes one’s complement B data and it send to 4_bit adder. The carrier input value is 1 at subtraction. so it’s form two’s complement of B data in 4-bit full adder.

And also sanjeev taugth me, to align block in order to reduce area and to create data bus with multiplexing two inputs.

First digit on clock

– Logeshwari

In electronics, initially I displayed my name using Seven Segment Display(SSD). I had already posted that in My First Blog. After that I wanted to learn more on SSD. So I was asked to make a digital clock. I have completed the first digit of the seconds. I used two JK flip flops (HD74LS76A), decoder (SN74LS47), a SSD (Common Anode) and Signal Generator. I first made the connections of JK flip flop on a breadboard. The input is clock signal which is generated from a signal generator of Frequency 1Hz. The combination of the two flip flops acts like a counter. Once the circuit is connected, I tested the output of the flip flop using an ocilloscope. I got the waveforms like this.

Then I took the decoder and connected the outputs to the input pins of the decoder. Decoder (converts the binary information to 2n outputs) is connected to the seven segment display. While doing decoder I was able to recall Karnaugh-Map which is the logic behind it. The output of the decoder is fed to the seven segment display. Once everything is done then it counts from zero to fifteen (f-represented in binary).


Since the one’s digit of the clock counts only upto nine and after that it should reset to zero. For resettting the digit to zero I used NAND gate. Binary representation of nine is 1001. When the Most Significant Bit and the Least Significant Bit are high(1) then it should reset to zero.


I have completed the first step only, but I feel happy that I learnt and understood what I did. I acknowledge Sanjeev, Sundhar and Ranjith for guiding me.

Sinthanai Sangamam with around 600 teachers(Azim Premji Foundation)


Sinthanai Sangamam is happened on 21/02/2018. It is a new kind of experience with around 600 teachers from different places. I have presented a paper about STEM land. The great thing is I got an opportunity to share about, my journey with the children in STEM land.The wonderful thing is that I am in STEM land. Why I came to STEM land is, I want to learn more about electronics that is why I came to STEM. I have learned about electronics what I have learnt that came as a few product that is inverter, display my name using 7-segment display, mobile charger, solar powered charger etc..Then I learned some of the programming from students that is scratch and geo gebra these program will be used in mathematics. These things I have explained in very shortly. In Sinthanai Sangamam everyone shared their experience with the children. How they interact with the children, what method they are following in their school, what kind of projects their students done and how we can connect to science and maths in our real life. The one main thing what I learnt is there should not a gap between children and teacher.

VLSI Layout

In VLSI layout course I learned to design a gates using NAND. Then I have checked the NAND gate truth table with the help of bread board, battery and multimeter. I learned to use magic tool, how to extract and how to simulate the layout.

I learned the cross section of CMOS and what colour coding we have to use for the each components.

Projects for Raman awards – Isaiambalam

Raman Young Science Innovator Award is a contest for students studying from III to X standards grouped into three. Students from IIIto IV, V to VIII and IX to X. We heard about this contest and started registering for it on 31st January. The registered students got their login credentials through their mail after 31st January. We submitted their projects on the last date on 10th February (extended to 12th February). Eight students submitted their innovation projects from Isai ambalam School. They are Ayush Jena, Suresh and Vasanth Kumar from class VII. Balamurugan, Kaviya, Sabari anandh and Yuvasri from class VI and Sharani from class V.

Ayush Jena (Class VII)
Ayush chose the topic buoyancy. He made an animation using scratch which explains the buoyancy of ships.

Suresh (Class VII)
He made his project on conductors and non-conductors.His main objective of the project is to find if the material is a conductor or non-conductor.He made a circuit and placed in inside a box.If the material is a conductor then the light will glow. If the light doesn’t glow then the material is not a conductor(non-conductor).The materials he used to make this project are wires, bulb, battery, box and iron.

Vasanth Kumar (Class IX)
Vasanth Kumar chose the topic Plant Kingdom. He took banana and he made an animation using scratch.In his animation he explained the benefits of bananas, scientific names and different things about it.

Balamurugan (Class VI)
He chose the topic density. He took a bowl of water and filled water upto 100 ml. Then he put some stones in the bowl until the water level rises to 110 ml. Then he took the stones in the bowl and weighed them with a weighing machine. It was 100 gm, which is equal to the rise in the water level.

Kaviya (Class VI)
Kaviya made her project in convection. She experimented by using coloured ice cubes. She was able to see the colour of the ice cubes get sink in the water. She observed that the speed of the speed of the ice cubes dissolving in water.

Sabari Anandh (Class VI)
Sabari chose the topic Plant Kingdom.He made his project using scratch. He selected neem, squirel, mamgo and described their important characteristics. Then he explained what is the connection between them using scratch.

Yuvasri (Class VI)
Yuvasri chose the topic melting point. She tested the melting point of ice cubes. She understood why the ice cubes melts when heated and what happens when heated.

Sharani (Class V)
Sharani chose the topic density. She took honey, vegetable oil, soup oil, coloured water and syrup. She poured all the liquid one by one glass bottle. Honey settles down because it has density greater than one. Similarly she formed five layers in the bottle.

Learning Festival at Indiranagar higher secondary school in Pondicherry

Learning festival was a workshop which happened in Indiranagar HSC. The workshop was happening for 4 days and we went for 2 days. We were invited to do some session regarding basic electronics. We decided to light up children’s name using a 7 segment display. We took 6 voltage sources, batteries, wires, extension chords, strippers, multi meters, 7 segment displays and our STEMland brochures. On the first day we had three sessions. we started the session with few minutes of concentration. We were informed that per session we will have about 30 students and 4 teachers.



  Day 1

On the first day the first session was handled by Sanjeev and we all supported him. We got 30 students and we split them in a group 3 to 4. He started the session by showing the example name board made by Saranya. Then he introduced the multi meter. In multi meter he showed them continuity mode. He explained how that once they connect two probes from the multi meter they will receive a beep sound. After that he introduced 7 segment display. Then he gave a 7 segment display to each student. Then asked them to draw it on their note. Next he show how to connect a multi meter with a 7 segment display to light up each segment. He asked them to find pin connection for each  segment. When students figured the pin connection connection he introduced bread board connection to the children. He explained bread board connections and how it works. Then each one of us started to support them in small group. Since we were running out of time. At end of the session children and teacher were able to light up at least 2 alphabets using the display.  Children and teacher felt that they learnt something new and they were excited when they lit the first alphabet with the display. Then the next two session was handled by Sundar. After the session we went around to see other events that were happening in the workshop.

  Day 2

On the second day we had 5 session and each session was handled by a facilitator from STEM land. The first session was handled by Saranya, Ranjith, logeshwari, Poovizhi and Pratap. We also two children from Isai Ambalam School to support us. These two children actually did a great job in handling a group and engaging all the children in their group.


A Student who came for the first session couldn’t accomplish what he wanted accomplish. His name was John and he asked that he wanted to come tomorrow to finish his name.We told him to come. Then the next day he turned up and started to connect the 7 segment display to light up his name. He was able to lit his name before lunch time. Then he started to handle a group in the afternoon. The boy was able to inspire a teacher who came to visit our session. Then the teacher also started to learn and he was able to light up 3 alphabets. In the evening the education minister came to meets us that time John showed his work to him and it was an inspiring moment.


Inverter with Arduino

Barani from 8th standard wanted to learnt something in electronics. He came and asked that he wanted to build an inverter using a Arduino. It was new for me so I told him lets learn together. Then we took all the components that are need to build a inverter. We started by writing a code to blink a LED at 50Hz. Then we dumped the program in the Arduino. Then we connected it with a CRO to see the square waveform. The square waveform was generated and we were able to see it. Then we connected the remaining circuit on bread board. We used a voltage source from which we got 9 volt DC input and fed it to a transformer. The transformer was giving 230 volt AC output. Then we connected a 5 Watts bulb to the output. The bulb turned on. We leant That using a 9 volt DC supply can give a 230 volt AC output. We really enjoyed doing that. During the week we had a Skype call with a school in Italy. Barani was able to explain the whole process to them. He felt very happy to show and share his project and learnings to them.

Half wave and Full wave rectifier

I made a model of Half wave and Full wave rectifier using LT spice.

Half wave rectifier:

A half wave rectifier is a device which makes use of properties of a pn junction diode. A PN junction diode only allows the current when it is forward biased. When it comes to real life application we need DC voltage. This circuit converts AC to DC voltage.

Full wave rectifier:

A full wave rectifier uses two PN junction diode which is more efficient and burns less power. It uses both the cycles of the AC wave and gives a smooth curve.

Salvaging wires and hacking a 240V to 9V transformer from an adapter

The 7th graders from Udavi School took a project on creating a PA system. To start of we required a lot of wires so the quest for salvaging wires began. The students picked every wire possible in STEMLAND that was not being used, we had a long Ethernet cable that was damaged and removed the outer casing and rolled up the inner wires. Once the required amount of wires were acquired we needed a power supply, a broken adapter that was found among the damaged equipment’s came into good use. We opened the case and took the transformer.

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Then the primary and secondary winding s were checked for connectivity using a multi-meter.

Next the transformer was hooked up to a plug and carefully soldered and covered using heat shrink cables for maximum protection from the input voltage, thus it was ready to be tested.

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The output of the transformer was connected to the oscilloscope, but only showed 2V to 3V. But when tested with a multi meter it showed 8.5V the expected voltage. This was a little confusing. In the end  by accident after removing the power we touched the transformer it was really hot. the adapter that the transformer was salvaged must have had burnt the core of the transformer, a while back. Then the hunt for a new transformer began.

Hardware clock

Recently the STEMLAND name board made using SSD had got dim and the 7th std students took it as a project to fix it. They de-soldered the dim SSD’s and Replaced it with new ones.

Barani got interested in the SSD’s and started powering them up using the Arduino, he manged to code the Arduino to print all the numbers 0-9 using two SSD’s

Then to take a step further he started his quest to build a clock. He had added a counter to light the corresponding diodes  in the SSD along with Sanjeev, this was done using a 9V battery.

As I already mentioned in my blog that Deepanam children built an oscillator. Bharani used the output of the oscillator as an input and made the clock count from 0 to 9.

Bharani making the clock count by removing and inserting the input each time.

Giving input from the oscillator built by Pravina (Deepanam kid).

Arun and Sundar


Pre Amp

In Stem land I was trying to repair a preamp which was not working. I opened it and I tried to find the problem. The problem was that the circuit wasn’t connected properly. I made the connection. The preamp needs an Ac input 9 V and 1A  transformer. We bought the transformer and made a cover for the transformer in the Stem land with the 3D printer. The green box was made by 3D printer. Now the preamp works.


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