ABCD Of ‘E’ – ABSOLUTE BEGINNER’S CIRCUIT FOR DEMONSTRATION OF ELECTRONICS

A workshop aimed at instilling the maker spirit and providing a hands-on experience in the domain of electronics.

Apoorva Mahajan, Kartikay Golcha, Ritu Prasad, Riddhi Luthra, Rolly Baradiya, Satyarth Rai, Siddharth Sharma

Introduction

ABCD of E - Poster
ABCD of E – Poster

The event commenced on the morning of August 13, 2016 at 9:30 am in the Mini-Auditorium of NSIT, New Delhi, with an active participation of 135 students from diverse branches of B.E., assisted by a team of about 30 mentors. The sole aim of the workshop was to enliven their journey into the astonishing world of electronics. To accomplish this objective, they were made to start from scratch and after a toil of two days, they took along a standalone project, built entirely by them: an ANALOG COLOR MIXER.

What is Analog Color Mixer?

Do you understand the difference between green and sea green? Are you captivated by a particular red shade? Are you a perfectionist and want the exact shades while matching clothes? Or are you an artist and want more colors on your palette? Then, this color mixer is a perfect tool for you! It uses three potentiometric controls to vary the individual intensity of Red, Green and Blue color of an RGB LED. With just these three potentiometers, one could set the RGB to almost any color!

 

Project Demonstrations

What better way to introduce absolute beginners to the enchanting world of electronics than to show them some finished products and projects designed and fabricated by students like them! The journey was embarked by inaugurating the event using the Inauguration Lamp-a patented project by CEDT, NSIT. Participants were briefed about its working and its commercial applications and feasibility. Following this, a recorded video of Prof. Dhananjay V. Gadre was played in which he welcomed all and emphasized on the DIY concept. Next in line, a series of projects were demonstrated by senior mentor, Nikhilesh Prasannakumar along with the underlying principles being discussed. This activity captivated the audience and awe-inspired them. Post project demonstration, a variety of experiments were performed which illustrated the use of speaker as a microphone, application of motor as a generator, use of LED as a sensor and working of a peltier module.

Nikhilesh Prasannakumar demonstrating projects and experiments

After a break of 15 minutes, the session resumed and was headed by Riddhi Luthra and Apoorva Mahajan( 3rd Year, ECE, NSIT) in which participants got acquainted with Printed Circuit Boards (PCBs) and got a glimpse of what exactly they would achieve at the culmination of the two-day long workshop. The discussion began with the idea of building electronic circuits on a simple breadboard. Those who were new to it, were introduced to this most fundamental electronic circuit prototyping board. The temporary and unreliable connections, the heavy weight of the breadboard, its non-usability in portable projects paved way for the need of PCBs. Printed Circuit Boards along with being durable, light in weight, ensure firm and stable connections and can be made custom-sized. The participants were informed about the PCB design software: EAGLE CAD used to design layouts.

After an insight into the world of PCBs, the participants were informed about the intricacies involved in fabricating a PCB using the most convenient home-made method known as Toner- Transfer Method. Starting from the sanding of the 1.6 mm thick copper clad boards (with 36 microns of copper) to remove the oxide layer, the various processes involved in the PCB fabrication were explained in detail. An illustrative power point presentation aided in visualizing the processes better.

The Toner-Transfer Method

The PCBs are made using copper clad boards which are essentially copper sheets laminated onto non- conductive substrates (Epoxy resin, FR4). The Toner-Transfer method involves the transfer of ink/toner from the print of the circuit on a glossy paper onto the copper clads. This transfer is done using an ironing press by applying uniform heat and pressure. After that, the paper is removed gently with the help of water. The excess copper (not underneath the ink) is then etched off the board using FeCl3 solution. After that the ink is removed using a scrub and the exposed copper tracks are prevented from oxidation using an acrylic film spray. The vias are drilled and components are soldered on the board. The flowchart of the various steps involved is shown below.

Fabrication Process

The students were divided into two groups and while one group departed for lunch, the other one commenced with the fabrication process. After an hour, the groups switched their activities.

Schematic of the Analog RGB Colour MixerBoard Layout of the Colour MixerParticipants were provided with a copper clad and board layout print each and a team of about 30 mentors assisted them at each stage of the process. The key points to be kept in mind while performing each step and the precautions to be taken were discussed. Also, the consequences of any step being carried out wrongly were informed. The boards were verified by the mentors before the participants proceeded to the next stage.

Day2

While some of the participants had got their PCBs completed, soldered and tested, most of the remaining participants were on the latter stages of the PCB fabrication process after Day 1. So about 50 participants resumed the drilling and soldering process at 8:30 am. They were provided with all the electronic components, wire cutter, tweezer, the schematic and board file as well as the Bill Of Materials (BOM) of the Analog Color Mixer.

 

Analog Colour Mixer BOM

Reference Value Note
C1 0.1uf SMD, 0805
C2 100uf Electrolytic, 16V
C3 0.1uf SMD, 0805
C4 0.1uf SMD, 0805
C5 0.1uf SMD, 0805
IC1 LM358N Op-Amp, DIP, 8 PIN
IC2 LM358N Op-Amp, DIP, 8 PIN
Q1 BD139 TO-126 package
Q2 BD139 TO-126 package
Q3 BD139 TO-126 package
R1 4.7Ω 1W
R2 4.7Ω 1W
R3 4.7Ω 1W
R4 1KΩ 1/8W
R5 1KΩ 1/8W
R6 1KΩ 1/8W
R7 10KΩ Pot
R8 10KΩ Pot
R9 10KΩ Pot
R10 100KΩ 1/8W
R11 100KΩ 1/8W
R12 100KΩ 1/8W
RGB LED 3W 6-terminal SMD
USB(POWER) Mini USB Connector

All resistors 5% CFR unless specified.

Additionally, a white coloured Table Tennis Ball, without any branding/marking on it will be required as a diffuser for the 3W RGB LED.

 

Components and Tools

A lecture aimed at explanation of the working of the circuit and its designing was conducted in two batches, by Apoorva and Riddhi starting from 10:30am. While the 50 participants continued their fabrication, the remaining got engaged in understanding the theory of the circuit they were fabricating. The interactive session began by taking up feedback and doubts from the fabrication process and some quizzing on the identification of the components received by the participants. Each component, its shape, size, specifications and its location in the board layout was deliberated upon, in reference to the BOM given to the participants, along with the components. The reasons for resistors having colour coded bands and not printed values on them, the significance of the 4 band and 5 band colour codes were discussed.

Moving on to the circuit, which was essentially a variable color display utilizing a 3W RGB LED, various kinds of LEDs available were discussed! The applications of the color mixer were talked about. Great ideas were put forward by the participants, ranging from a lamp at home to forming particular colors as a game! The circuit is, in fact, a good learning tool for kids to understand the composition of colors.

Then the discussion went on to lighting up a single LED. The calculations of the resistor in series depending upon the cut- in voltage, considering the worst case possibility were done. Next, the concept of variability in light intensity using a potentiometer was introduced. In the Analog Color Mixer, each control lets the corresponding color to light up from null to max intensity. That’s the beauty of the circuit!

With just the potentiometer, it isn’t possible. It is difficult to set the RGB to zero intensity in a purely analog implementation. So, one of the basic building blocks: Op-amp or an Operational Amplifier was introduced. The golden rules of an ideal Op-amp were taught. A simple exercise, to find the gain of inverting and non-inverting amplifiers helped the participants get a better grasp over Op-amps. The use of a dual Op-amp IC: LM358 was made clear and the final schematic was thoroughly explained. The use of a transistor to overcome the output current limitation of the Op-amp was explained. The transistor amplifies the output current, allowing a large current of 300 mA as required by the high wattage LED. The additional capacitors to filter various types of noise were discussed too. The lecture continued for about two and a half hours. By this time those 50 participants had got their boards soldered and tested. The two groups switched their activities at 2:00pm. The entire lecture and testing was completed by 6:30pm.

 

A few days later, a short session was held by Prof. Gadre where he interacted with the participants and distributed the certificates.

Overall, this Analog Color Mixer circuit proved to be a great learning experience for the participants, giving them a visual treat, teaching them the basics of lighting up a simple LED, making them acquainted with transistors and Op-amps and a variety of components available, ranging from a 3W RGB SMD LED to SMD capacitors and high wattage resistors! Not to forget the first time experience of soldering so many different types of components!

“Kuchh banane ke liye, kuchh ukhaadna padta hai. So aaj kya ukhaada?”

-Prof. Dhananjay V. Gadre