Welcome to my website! I'm Vivek Chandra, and here I showcase projects related to electronics that I've explored during my bachelors and masters in the physics laboratory. My focus is on delving into the principles and theories behind these projects, highlighting the results we can obtained, and discussing the valuable insights that we can learn from them.
I designed a battery charging circuit suitable for both 6V bike batteries and 12V car batteries. The circuit utilizes a step-down transformer, a bridge wave rectifier, and a two-way switch for voltage selection. To complete the project, I housed the circuit in a box acquired from a scrap dealer, ensuring a functional and compact solution for battery charging needs. Here’s the circuit diagram below.
Physics behind it:
(a) Stepdown transformer: This device converts 220V AC to either 12V or 6V, utilizing the principle of electromagnetic induction.
(b) Two-way switch: The switch is used to select between 6V and 12V voltage output.
(c) Bridge wave rectifier: The bridge wave rectifier converts alternating current (AC) into direct current (DC) by using a network of four diodes in a bridge configuration, ensuring current flows in one direction, resulting in a DC output.
While exploring an old CRT TV at my father’s electronics shop, I discovered an IC labeled TDA 7297. After some research, I learned that this IC can serve as an amplifier circuit, capable of driving sound to two speakers. I’ve utilized a circuit diagram, which I’ll share below.
Physics behind it :
The TDA 7297 specifically operates by receiving low-level audio signals, processing them through its internal circuitry, and then delivering higher power output to drive speakers. This amplification is achieved through transistors or integrated circuits, enabling the faithful rendition of sound with greater volume and clarity.
I power the amplifier using a 12V battery charger, and I input audio signals through an auxiliary (aux) cable, which can be connected to mobile phones or laptops. To minimize external noise, I’ve incorporated a 104pF capacitor, serving as a noise filter in the circuit.
I’ve designed a circuit that wirelessly detects the presence of AC current flow in a wire. When AC current flows through the wire, an LED indicator lights up, signaling its presence. However, if there is no AC current flow, the LED remains unlit, as demonstrated in the video.
Circuit diagram that i use is given below :
Physics behind it :
In this circuit, NPN transistors act as switches. When a small microampere current is applied to the base, it creates an electric field allowing a much larger current to flow from collector to emitter. This amplifies the base current, illuminating an LED.
Four transistors are cascaded to further amplify the base current. The lowest transistor’s base is connected to a solenoid formed by rotating wire. If AC current passes through the wire, it generates a varying magnetic field, causing fluctuating magnetic flux. According to Faraday’s law of electromagnetic induction, this induces an electromotive force (EMF) at the lowest transistor’s base.
This induced EMF is then amplified, switching the battery and LED connection. Consequently, the LED lights up when AC current flows in the wire, revealing the presence of varying magnetic fields and the induced EMF.
In a fascinating encounter at my father's electronic shop, a physiotherapist needed help automating his device, which required a 1-minute on-time and a 5-6 second off-time. I crafted a custom astable multivibrator circuit with a 65-second on-time, a 5-second off-time, and added a relay for convenience. This not only showcased the practical application of physics but also highlighted the importance of understanding and catering to customers' unique needs. The outcome? A delighted customer and a valuable lesson in using technology to enhance people's lives, all for just 1000 rupees, here i use 5v instead of 220v and led instead of power socket to demonstrate it in video.
The circuit diagram that i use is given below:
An astable multivibrator is an essential electronic circuit that generates a continuous square wave output. This circuit capitalizes on the charging and discharging of capacitors, complemented by the switching behavior of transistors. By skillfully choosing the resistor (RA, RB) and capacitor values, you can precisely control the frequency and duty cycle of the output waveform.
In a video demonstration, we observed that the theoretical and practical values of Ton and Toff closely matched:
Theoretical Ton = 0.693 * (40kΩ + 3kΩ) * 2200μF = 65.5 seconds
Theoretical Toff = 0.693 * 3kΩ * 2200μF = 4.5 seconds
Practical observations in the video showed Ton ≈ 65 seconds and Toff ≈ 5 seconds. This alignment between theoretical and experimental values highlights the precision and predictability of this astable multivibrator circuit.
I’ve employed the LM338 integrated circuit to construct a variable voltage regulator, allowing me to adjust the output voltage with a potentiometer. While I previously created a voltage regulator using a zener diode, it had limitations, particularly in terms of low current output. Zener diodes are more suitable for providing reference voltage. In contrast, the LM338’s datasheet indicates a maximum current output of 5A, making it an ideal choice for building a mobile battery charger, which requires higher current capabilities for efficient charging.
LM388 also incorporates current-limiting features to protect the regulator and connected components.
The circuit diagram that i use is given below :
Physics behind it :
Voltage regulation relies on the principle of maintaining a stable reference voltage and utilizing feedback control mechanisms to adjust the output voltage, ensuring it remains constant despite variations in input voltage and load conditions.
The minimum voltage of 1.266V is in accordance with the theoretical formula, where Vo is expected to be approximately 1.25V when R2 is set to zero.
The maximum voltage of 12.72V, as shown in the video, is lower than the input voltage of 15V because the LM388 IC dissipates some power as heat when regulating the output voltage. This energy loss results in a slightly reduced output voltage, which aligns with the expected behavior of voltage regulators.
This circuit is particularly useful for repairing electronic gadgets. Imagine you’ve repaired a gadget, and for the final testing, you plug it into a direct 220V power socket. If the gadget has an internal short circuit, connecting the 220V phase and neutral wires could cause a spark at your home’s main circuit breaker (MCB), resulting in a power outage. However, with this protection circuit, if such a scenario occurs, the bulb on the circuit lights up, indicating that there’s a short circuit within the gadget. This added safety feature prevents disruptions to your home’s power supply and helps identify potential issues in the repaired gadget.
Here’s the circuit diagram below.
Socket-1 is connected in series with a bulb, while Socket-2 is in parallel with the 220V power supply.
Switch-1 controls Socket-1, and Switch-2 controls Socket-2 for on/off functionality.
Physics behind it :
In our circuit, when a gadget is internally short-circuited, current flows through the bulb in a series connection, dissipating its energy in the bulb, and then safely connects to the neutral without causing a blast or spark.
A customer visited my father’s electronic shop and expressed a desire to replicate the Marshall speaker, which typically retails for around 40,000 rupees. I accepted the project but made it clear that I wouldn’t be focusing on the decoration or aesthetics. Instead, I offered to create a home theater system with similar functionality as original, including a subwoofer, Bluetooth connectivity, tweeters, and speakers. I collaborated with a carpenter to craft the wooden enclosure and handled all the internal circuitry myself. I was able to deliver this product to the customer for 5,000 rupees. This experience not only provided me with a deeper understanding of how home theater systems work but also offered valuable insights into dealing with customers.
list of components that i used to design the home theater system :
Transformer (12-0-12 , 2 amphere)
Bluetooth module (purchased from market)
TDA2030 amplifier circuit board (purchased from market)
7805 IC to convert 12V to 5V for Bluetooth module power
Subwoofer (installed internally inside the enclosure)
2 speaker, 2 twitters, 3 potentiometers, Fuse, 3 potentiometers
Detachable power supply cord & switch
Integrators attenuate high-frequency components of input signals while allowing low-frequency components to pass through. This filtering action is valuable for reducing noise and interference in various applications.
Useful applications include waveform shaping, where it can convert square waves into triangular or ramp signals-to-parabolic waveform transformation, as shown in the output of oscilloscope below.
Circuit diagram :
(i)Ideal integrator
(ii) Practical integrator
Explanation as integrator
Explanation as low pass filter
Oscilloscope output is given below:
Input = square wave (green)
output= Triangular wave (orange)
Input = Ramp (green)
output= parabolic (orange)
A differentiator, often implemented with an op-amp, calculates the rate of change of an input signal. When a square wave is differentiated, it yields high-frequency spikes, resembling a Dirac delta function, as shown in the output on the oscilloscope below.
Differentiators are valuable as high-pass filters in applications like signal processing, where they enable high-frequency components to pass through while attenuating low-frequency ones.
Explanation as differentiator
Explanation as high pass filter
Oscilloscope output is given below:
Input = square wave (green)
output= spike wave (similar to dirac delta) (orange)
Input = sine(green)
output= cos (orange)
A comparator is an electronic circuit that operates as a high-gain, open-loop amplifier. Its primary function is to compare two input voltages and output a logical high or low signal based on which input is greater.
For example in a thermostat, a comparator can detect when a room’s temperature falls below a set point and trigger the heater, providing an on/off control mechanism to maintain a desired temperature.
Circuit diagram
Working of comparator
Input = sine wave (green)
output= square wave (yellow)
A Schmitt trigger is a type of comparator which has two different voltage thresholds for switching between its high and low states. A Schmitt trigger has two different voltage thresholds for switching between its high and low states.
For example in a digital input circuit, a Schmitt trigger can help eliminate noise or jitter in a signal, ensuring a clean and reliable transition between logic levels.
(i) Circuit diagram
(ii) output
Explanation
Oscilloscope output is given below:
Input = sine wave
output= square wave
A voltage limiter uses a zener diode to restrict output voltage within a predefined range. This prevents the voltage from exceeding or falling below the specified values.
This is useful in applications like audio signal processing to protect speakers from over-voltage or under-voltage conditions.
(i) Circuit diagram
(ii) output
Explanation
Oscilloscope output is given below :
Op-amps typically operate with dual power supplies of ±15V along with a ground reference. In cases where a single 9V battery is the only power source available, we can employ a voltage divider technique to create a virtual ground at around half the battery voltage (4.5V). This setup effectively simulates a dual power supply, allowing us to use the op-amp with a single 9V source.
Here i demonstrated it in “LTSPICE” which is circuit simulation software.
I designed a inverting amplifier circuit with a gain of 2. For the input, I used a sine wave with an amplitude of 1V and obtained an inverted output with an amplitude of 2 volts, as depicted below.
Input= Red colour
Output= Green colour
10. Asynchronous up counter
An asynchronous up counter is a type of digital counter circuit that counts upward in binary sequence. It's called "asynchronous" because the flip-flops in the counter change state independently, without being synchronized by a common clock signal. Each flip-flop in the counter triggers the next flip-flop, and this creates a ripple effect where each stage of the counter changes state one after the other. Counters can be used to keep track of time by incrementing values at a regular interval, allowing us to display hours, minutes, and seconds accurately. I use IC 7476.
IC 7476 pinout
Clock signal using function generator
(a) 2-bit aynchronous up counter
Practical demonstration video is given below :
(b) 4-bit aynchronous up counter
Practical demonstration video is given below :
11. Ultrasonic Vision: Smart Glasses for the Visually Impaired
Arduino:
Arduino is an open-source electronic prototyping platform enabling users to create interactive electronic objects. Arduino board designs use a variety of microprocessors and controllers, they are equipped with sets of digital and analog input/output (I/O) pins that may be interfaced to various expansion boards or breadboards and other circuits. The microcontrollers can be programmed using the C and C++ programming languages, using a standard API which is also known as the Arduino language.
For our project we used Arduino UNO R3 with the microcontroller ATmega328 chip. We have written our code in C++ for our project
Motivation:
Currently there are an estimated 4.95million blind persons in India. As we know they are always in need of guidance for mobility. There have been several systems designed to support visually-impaired people and to improve the quality of their lives. Unfortunately, most of these systems are limited in their capabilities. In our project we built an assistive device which will help in independent mobility to visually-impaired people. The need for assistive devices for navigation and orientation has increased. The simplest and the most affordable navigations and available tools are trained dogs and the white cane. Although these tools are very popular, they cannot provide the blind with all information and features for safe mobility, which are available to people with sight.
Theoretical explanation:
In our Project we used ultrasonic sensors for the detection of objects. The HC-SR04 Ultrasonic Distance Sensor is a sensor used for detecting the distance to an object using sonar. An ultrasonic sensor can convert electrical energy into acoustic waves and vice versa. The acoustic wave signal is an ultrasonic wave traveling at a frequency above 18kHz. The famous HC SR04 ultrasonic sensor generates ultrasonic waves at 40kHz frequency. The sensor also has an ultrasonic receiver, which receives the reflected ultrasonic signal. Depending upon the time taken for the sound wave to hit an object and return back, the distance of the object from the sensor is calculated.
Ultrasound is a high-pitched sound wave whose frequency exceeds the audible range of human hearing. It has a frequency over 20,000 Hz .
Working of Ultra sonic sensor is illustrated by the following figure:
VCC - supplies power to the HC-SR04 ultrasonic sensor. We can connect it to the 5V output from Arduino.
Trig (Trigger) - pin is used to trigger ultrasonic sound pulses. By setting this pin as HIGH for 10µs, the sensor initiates an ultrasonic burst.
Echo - pin goes high when the ultrasonic burst is transmitted and remains high until the sensor receives an echo, after which it goes low. By measuring the time, the Echo pin stays high, the distance can be calculated.
Gnd - is the ground pin. It is connected the ground of the Arduino
Circuit Diagram:
Code:
#define trigPin 8
#define echoPin 7
#define buzzer 12
#define vibrationPin 2
void setup()
{
Serial.begin(9600);
pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);
pinMode(buzzer, OUTPUT);
pinMode(vibrationPin, OUTPUT);
}
void loop()
{
long duration, distance;
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);
duration = pulseIn(echoPin, HIGH);
distance = (duration * 0.034 / 2);
Serial.print(distance);
Serial.println(" cm");
if (distance <= 30)
{
tone(buzzer, 500, 500);
digitalWrite(vibrationPin, HIGH);
}
else if (distance > 30 && distance < 62)
{
tone(buzzer, 500, 100);
digitalWrite(vibrationPin, LOW);
}
else
{
digitalWrite(buzzer, LOW); digitalWrite(vibrationPin, LOW);
}
delay(200);
}
Working:
The above schematic is assembled on glasses. The transmitter emits ultrasonic signals continuously and the receiver receives any reflected waves. A threshold distance is set and if there is any object or obstacle at a distance closer than this, then the buzzer is activated with vibration and it alerts the person. We can set the threshold distance as an input while writing the code. There are certain limitations to this, one of them is the distance of obstacle i.e., any obstacle at a distance greater than 13ft cannot be detected.
RESULTS:
The code is written in C++, we assign certain names to the pins. The time taken by the ultrasound echo to reach the sensor is taken as input. The code has the distance formula included. The loop runs again and again at regular intervals and gives us the distance as output. There is also another loop which takes this distance as the input and compares it with the Threshold distance. The Threshold distance of the sensor is set to 62 cm. When the person wears these spectacles and faces an object or obstacle closer than 62cm, then the buzzer starts beeping. When the distance further decreases very less than 62cm i.e., between 0 and 30 cm, then the frequency of buzzer increases rapidly and vibration motor also starts. The key feature is that, the distance of the object from the sensor is also shown in the running code.
