Tuesday, 26 July 2016

Musical Light Using Op Amp

How it beautiful it looks when LED blinks with the music or your voice.

Here I have made this using only two opamp.

First Op Amp for amplification of signal coming Out from microphone and the second one as a comparator .

I have set a reference voltage level. when the signal cross the limit the out put becomes high and LED turn ON. It's happens so fast looks very beautiful. jyotshna.com

Here is a video demo Of my prototype

Making a microphone pre amplifier using Opamp

Listing own voice on a speaker through a hand made microphone is fun stuff. I had some  electret microphones that I have salvaged from old phones.

why we need a mic preamp?
microphone is a transducer. It's output voltage is very low few millivolts only. But to drive a loudspeaker you need lot of power. so you need amplification. But If you put so less voltage to power transistor base nothing happens. Its requires a certain voltage or current to work with. Hence we need amplification of signal before feeding it to power amplifier stage. preamplifier exactly does that thing.

In my prototype I have uses a common Op Amp IC LM324 . It is not perfect for this but OK.
It works like a non inverting Amplifier with negative feedback.

Here Is the circuit Diagram jyotshna.com
Here is the image of my prototype

Sunday, 24 July 2016

Poor student's sound card Oscilloscope

Every electronics enthusiastic feels a need of oscilloscope . Mostly when working on switch mode circuits or the signal circuits.
Oscilloscopes are very costly even most entry level scopes.
So I decided to make my own basic scope.

Here We have used a external USB sound Card and a computer software.
Download the software from this link

How it Works
Our voice signal is an analog signal . a microphone receives it and sends it to the soundcard . The sound card has a built in analog to digital converter. then it sends the digital information to CPU for processing. Here the software processes the information and displays in a graphical user interface .

Make the signal Probe

Sound Card are normally very sensitive to input voltages . Its input voltage must be limited to 0.6 to 0.8 volts for safe operation. there we have used resistors to drop input voltage to a safe limit. the variable resistor is used to vary the input gain. here we have two diodes back to back for safety. If any cycle positive or negative has an output more then 0.7 volts one of the diodes turns on and bypasses the current keeping the soundcard safe. I have used here cheep chinese USB sound card rather than my costly internal card. There is a option of source select. you can use an headphone microphone jack to give input to internal sound card.

 c1 is optional.

Here I have used arduino fed program to generate an pulse width modulated signal.

Here is a video demo.

Breathing LED using 555

We can make make a breathing LED by various methods . The basic requirement is that we need an slow amplitude varying voltage source . That's may be a capacitor charging and discharging ramp signal of average pulse width modulated signal.
When We used arduino fading program we uses pulse width modulation technique to make breathing led.

In astable mode of 555 timer the timing capacitor charges upto 2/3 vcc and then again discharges. There is a time varying ramp signal across the capacitor We can utilize the signal for led breathing. 

Here is the circuit Diagram
pin 2 is connected with the threshold pin of 555( pin no 6). that is the non inverting input of one of the internal comparators.
It works like a op-amp voltage follower. the LED brightness varies with the base current of the transistor.

Here is the simulated signal Output

Friday, 15 July 2016

Simulation Of Amplitude Modulation Using 555 and Ultra High Frequency transistor

Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. In amplitude modulation, the amplitude (signal strength) of the carrier wave is varied in proportion to the waveform being transmitted.

This technique is used in old day's radio Broadcasting before FM(Frequency Modulation).

AM has some advantages over FM.

1- Coverage area of AM Receiver is wider than FM because atmospheric propagation
2- AM is long distance propagation because λ
3- AM Circuit is cheaper and non complex than FM.

Here I have a simple demonstration how the amplitude of a information signal is modulated with the higher frequency carrier signal. 

Here is the circuit Diagram
I have uses proteus ISIS software for simulation Purpose.

here is the Output

World's simplest Oscillator / Esaki Oscillator

Reona Esaki (江崎 玲於奈 Esaki Reona, born March 12, 1925), also known as Leo Esaki, is a Japanese physicist who shared theNobel Prize in Physics in 1973 with Ivar Giaever and Brian David Josephson for his discovery of the phenomenon of electron tunneling. He is known for his invention of the Esaki diode, which exploited that phenomenon. This research was done when he was with Tokyo Tsushin Kogyo (now known as Sony). He has also contributed in being a pioneer of the semiconductor superlattices.

Here is the circuit of oscillator he invented
How it Works?

Here the transistor is connected in reverse direction.In this condition no currents flows through the transistor.
But if applied voltage is greater than the breakdown voltage ,current will start flowing. here the voltage across the capacitor does this work. And base of the transistor is left open.
As the capacitor discharges through the transistor and LED the voltage goes down and the transistor goes off and the capacitor again starts charging. Hence the cycle repeats and the circuit works as an oscillator.
By varying the potentiometer position we can vary frequency. 

A video demo

Simple BOOST conveerter

According To wikipedia
boost converter (step-up converter) is a DC-to-DC power converter steps up voltage (while stepping down current) from its input (supply) to its output (load). It is a class ofswitched-mode power supply (SMPS) containing at least two semiconductors (a diode and a transistor) and at least one energy storage element, a capacitorinductor, or the two in combination. To reduce voltage ripple, filters made of capacitors (sometimes in combination with inductors) are normally added to such a converter's output (load-side filter) and input (supply-side filter).

circuit Diagram and Operation
when transistor is on
when Transistor Is off
Output voltage = supply voltage + voltage across the inductor

Here, I used the pulses from a 555 timer to make transistor on and off. I collected the inductor from a burnt cfl ballast.

Here is an video of my prototype

Light Dimming / DC motor speed control using 555

What is PWM actually?
It's simply controlling the width of the high and low pulses to do something useful. It may be encoding a massage or controlling average voltage.

according to wikipedia 

Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a modulation technique used to encode a message into a pulsing signal.

Voltage Control Application 
Here I have made a simple pulse width modulator using 555 timer.

Here is the circuit Diagram

You can also place a LED in the place of DC motor to control it's brightness.

How the circuit works?

The reset pin is connected to +V, so it has no effect on the circuit's operation.
When the circuit powers up, the trigger pin is LOW as capacitor C1 is discharged. This begins the oscillator cycle, causing the output to go HIGH.
When the output goes HIGH, capacitor C1 begins to charge through the right side of R1 and diode D2. When the voltage on C1 reaches 2/3 of +V, the threshold (pin 6) is activated, which in turn causes the output (pin 3), and discharge (pin 7) to go LOW.
When the output (pin 3) goes LOW, capacitor C1 starts to discharge through the left side of R1 and D1. When the voltage on C1 falls below 1/3 of +V, the output (pin 3) and discharge (pin 7) pins go HIGH, and the cycle repeats.
Pin 5 is not used for an external voltage input, so it is bypassed to ground with an 0.01uF capacitor.
Note the configuration of R1, D1, and D2. Capacitor C1 charges through one side of R1 and discharges through the other side. The sum of the charge and discharge resistance is always the same, therefore the wavelength of the output signal is constant. Only the duty cycle varies with R1.
The overall frequency of the PWM signal in this circuit is determined by the values of R1 and C1. In the schematic above, this has been set to 144 Hz.
To compute the component values for other frequencies, use the formula:

Frequency = 1.44 / (R1 * C1)
Here is my prototype

Here is a demo video of my prototype

Wednesday, 13 July 2016

Frequency Counter Using Arduino

Currently I am working on switch mode power converters . Here frequency is a very important factor, but I don't have any frequency counter .so decided to make it of my own .
Here I used arduino as controller and watching the output in the serial monitor.
I used 555 timer in astable multivibrator mode. 7414 inverting schmitt IC is used to make digital output.

Here Is the arduino code

#include <FreqCount.h>

void setup() {

void loop() {
  if (FreqCount.available()) {
    unsigned long count = FreqCount.read();

Here is a video Of my prototype

Basic Oscilloscope Using Arduino

As I am a poor person ,I can not afford an oscilloscope even most entry one. Currently I am working on switching power converters so I badly need to see the waveform. 
Then I thought to build a DIY scope with the components I already have. I searched the web and found the solution.

I have arduino uno and downloaded Processing IDE from this link http://processing.org/

I used 555 timer as a simple square wave oscillator. and connected it with arduino analog inputs. Connected arduino board with USB cable to my laptop.
now here I have done two steps .
Upload code to the arduino IDE.
code is here-
#define ANALOG_IN 0

void setup() {

void loop() {
  int val = analogRead(ANALOG_IN);                                              
  Serial.write( 0xff );                                                         
  Serial.write( (val >> 8) & 0xff );                                            
  Serial.write( val & 0xff );
Step two
Upload code to the Processing IDE
Code is here-

import processing.serial.*;

Serial port;  // Create object from Serial class
int val;      // Data received from the serial port
int[] values;
float zoom;

void setup() 
  size(1280, 480);
  // Open the port that the board is connected to and use the same speed (9600 bps)
  port = new Serial(this, Serial.list()[0], 9600);
  values = new int[width];
  zoom = 1.0f;

int getY(int val) {
  return (int)(height - val / 1023.0f * (height - 1));

int getValue() {
  int value = -1;
  while (port.available() >= 3) {
    if (port.read() == 0xff) {
      value = (port.read() << 8) | (port.read());
  return value;

void pushValue(int value) {
  for (int i=0; i<width-1; i++)
    values[i] = values[i+1];
  values[width-1] = value;

void drawLines() {
  int displayWidth = (int) (width / zoom);
  int k = values.length - displayWidth;
  int x0 = 0;
  int y0 = getY(values[k]);
  for (int i=1; i<displayWidth; i++) {
    int x1 = (int) (i * (width-1) / (displayWidth-1));
    int y1 = getY(values[k]);
    line(x0, y0, x1, y1);
    x0 = x1;
    y0 = y1;

void drawGrid() {
  stroke(255, 0, 0);
  line(0, height/2, width, height/2);

void keyReleased() {
  switch (key) {
    case '+':
      zoom *= 2.0f;
      if ( (int) (width / zoom) <= 1 )
        zoom /= 2.0f;
    case '-':
      zoom /= 2.0f;
      if (zoom < 1.0f)
        zoom *= 2.0f;

void draw()
  val = getValue();
  if (val != -1) {

Here Is my Prototype-

What is Inside a 78xx series linear regulator IC / How a linear works?

A linear voltage regulator is basically a resistive voltage divider network.
A voltage divider divides voltages across the resistor. Here we can use a zener diode for voltage stabilization .  But It’s performance is not satisfactory.
Here is the most basic circuit

We used zener and the variable resistance for reference voltage and that we fed to the power transistor base which is in emitter follower configuration . current through the transistor proportional to base current applied.

Note: In this circuit a minimum load RL must be always connected.
Above regulator is quit simple but it’s voltage varies with load. So we need an feedback for adjusting the transistors base current.

Here is the final most practical circuit- 
More Details will be added in future

Tuesday, 12 July 2016

open run of a chinese drill universal motor

Before buying a Chinese drill machine /Tear down a Chinese drilling Machine.

Today , I have received a faulty Chinese drill machine for repairing. I do not want to disclose the brand name here. It was of 800 watt,220 volt,50hz.costs around INR 1500.
As usual I opened the casing .And found that that the field winding is partially  burnt due to overheating. It was a winding short circuit issue.
It provides many features but the technology and the quality of material is very poor.

The most strange thing is its sped controller .Common Good branded drilling machines usually uses phase fired controller to control the universal mot6or speed. This method is little bit costly .
But this drill uses only a 500ohm resistor for controlling the armature current thus speed . It is now clear that It has only two speed stages, you can not vary speed according to your choice.
As it uses resistor, It spoils power as head.
Armature Quality is not also good.
One Good feature is that you can reverse the direction of motor rotation if needed. It does this by reversing the brush position.
It does not have any EMI and harmonics filter. A DC series motor produces too much harmonics and fed it to supply mains. So it has an adverse affect on other sensitive equipment running parallel in your home.
Here I have drawn a circuit by investigating its connection. It will help you during repairing.

So ,I recommend ,Don’t Buy this type Of drill Machines.