Category Archives: Circuit Diagram

Christmas LED Lights Circuit

Using this simple Christmas LED lights decoration circuit, you can make an 18 LED flasher to decorate the Christmas Tree. The White, Blue and Red LEDs flash at different rates to give a colorful display. It is a light sensitive circuit so that it will turn on in the evening automatically and stays on till morning.

The circuit uses the popular Binary counter IC CD 4060 to flash the LEDs at different rates. Components C1, VR2 and R1 form the oscillator and the output pins 7, 5 and 4 become high / low sequentially. When one output turns high, a set of 3 LEDs turn on and when the same output turns off, the second set turns on. This sequence is similar in the other two sets of LEDs also but with different timings. The speed of the Flashing can be controlled through VR2.

Christmas LED Lights Decoration Circuit Schematic

LDR is provided with VR1 to activate the IC in the evening. In day light, LDR conducts and keep the reset pin 12 of IC1 high to inhibit it from working. When the day light ceases, pin12 becomes low and the flasher starts working. VR1 adjusts the sensitivity of LDR at the required light level. If more LEDs are required, increase the supply voltage to 18 volt DC. The circuit can be powered using a standard 12-18 volt 500 mA adapter.Use High bright transparent LEDs for attractive display.


LDR PC Desk Lamp

Most of the PC desk lamps available in the market light up whenever there is an input power. These don’t take into account whether there is a real need for the light or not. Here is an intelligent PC desk lamp circuit that overcome the problem.
It senses the light level in the room to determine the actual need for light and lights up only if required. It is designed to work with the PC and remains on only when the PC in the table is in working state. It uses MOC3021.

Front end of the circuit is powered by the 5volt dc supply available from the usb port of the PC. When circuit is powered, the light sensor LDR (R2) resistance is low if there is sufficient light and thus most of the base current of transistor T1 finds an alternative easy path via LDR and T1 remains cutoff. While during dakness, the LDR behaves almost as an open circuit, and the current through sensitivity control preset pot (P1) and assosiated resistors (R1,R3) flows into the transistor’s base. As a consequence, T1 conducts to energise the opto-triac PC1. Next, the lamp driver triac T2 is fired through the opto-triac PC1 and switch on the power supply to the incandescent lamp.

The circuit can be constructed on a medium size PCB. After construction, enclose the finished circuit in a well insulated plastic cabinet. Then drill holes for mounting the ‘B’ type USB input socket, power switching termianls and the LDR etc. This circuit is meant for use in conjuction with Personal Computers to switch on an associated light sensitive table lamp/similar load. An optional electro magnetic relay can also be wired at the output of the circuit to switch heavy electrical load(s). For interconnection between PC and the control circuit, use a standard USB cable with an ‘A’ type connector on one end and a ‘B’ type connector at the other end.

LDR USB Desktop Lamp Circuit Schematic

Warning! This LED PC Desk Lamp circuit is perfectly isolated from mains. However some parts of the circuit carries dangerously high voltages. So ,while testing,using or repairing take extreme care to avoid the fatal electric shock.


Frequency counter circuit

You may have already seen various projects over many websites named Frequency counter, Digital Frequency Counter etc. I’m posting just another of them. Showing the use of timer/counter of AVR micro controller (Atmega8) in one of it’s form. This circuit can be used as a simple micro controller project for your engineering courses. Frequency of a periodic signal is the number of cycles it repeats per second!   So If we count the number of cycles recorded in a second it will directly read the frequency. So what we are going to make is a frequency counter circuit, which can also be called as a frequency meter.

To make this frequency meter 1) we need a signal (whose frequency has to be counted) 2) Atmega8 micro controller from Avr 3) An LCD to display the counted frequency. I assume that you are familiar with Avr Atmega8 and you know how to program it. You also need to know – How to interface LCD with Avr

Now let’s get into the details of the project – Simple Frequency Counter or otherwise Frequency Meter!

Take a look at the circuit diagram given below and also skim through the program given towards the end of this article.

Description of circuit:-

            So what I have done here is; Set the counter to zero, waited for 1S, and read  the counter again. But remember,you need to read the value immediately after the delay loop ends. It is simple. Just assign a variable and copy the count to that. The data type of the variable is essentially an unsigned integer. You can try floating point data type too! But here you need to typecast it! That’s all!  To read about floating point conversion in Avr – read this article carefully – String Formatting of Avr

                And yes! It’s better that you apply a conditioned signal for counting the frequency. i.e. a square wave or a trail of pulses. You may use a suitable signal conditioning circuit like Comparator  Schmitt trigger, sine wave to square wave converter, whatever suits you. If the signal is of low power, then use a conditioning circuit . You can get lots of signal conditioning circuits in this website – check here – Signal Conditioner Circuits

Now here is the Technical details of my project. I hope you’ll have not much problem to make this.

Battery charger circuit using SCR

A simple battery charger based on SCR is shown here.Here the SCR rectifies the AC mains voltage to charge the battery.When the battery connected to the charger gets discharged the battery voltage gets dropped.This inhibits the forward biasing voltage from reaching the base of the transistor Q1 through R4 and D2.This switches off the transistor.When the transistor is turned OFF,the gate of SCR (H1) gets the triggering voltage via R1 & D3.This makes the SCR to conduct and it starts to rectify the AC input voltage.The rectified voltage is given to the battery through the resistor R6(5W).This starts charging of the  battery.
When the battery is completely charged the base of Q1 gets the forward bias signal through the voltage divider circuit made of R3,R4,R5 and D2.This turns the transistor ON.When the Q1 is turned ON the trigger voltage at the gate of SCR is cut off and the SCR is turned OFF.In this condition a very small amount of charge reaches the battery via R2 and D4 for trickle charging.Since the charging voltage is only half wave rectified ,this type of charger is suitable only for slow charging.For fast charging full wave rectified charging voltage is needed.

Circuit diagram with Parts list.


  • Assemble the circuit on a good quality PCB or common board.
  • The transformer T1 can be 230V primary, 18V /3A secondary step down transformer.
  • The voltage of the battery at which the charging should stop can be set by  the POT R4.
  • The battery can be connected to the charger circuit by using crocodile clips.

Fritzing Software Download

Fritzing software is an interesting open-source initiative to support designers, artists, researchers and hobbyists to work creatively with interactive electronics and develop electronic projects. Fritzing helps you learn more about electronic circuits, to document your projects and even let’s you prepare them for production.

Fritzing Views

Once you have build your circuit on the breadboard you can start transfer it to Fritzing which has 3 different project views:

  • the breadboard view is where virtual electronic components can be wired and placed on a virtual breadboard. Parts that do not exist can be created as well.
  • the schematic view is where the former representation of the schematic can be viewed and edited. Changes made in one view instantly affect all other views.
  • the pcb view allows you to place parts on a printed circuit board. An auto-router generates the traces and the final pcb layout can be exported to the necessary production formats.

Publishing and sharing your projects is easy with the built-in function. Additionally the website offers learning material, tutorials and the option to take part in development of Fritzing.

This version includes translations for:
Deutsch (German), EnglishEspañol (Spanish), Français (French), Italiano (Italian), Nederlands (Dutch), Português (eu) (Portuguese EU), Português (br) (Portuguese BR), 日本語 (Japanese), 中文 (简体) (Chinese Simplified), 正體中文 (繁體) (Chinese Traditional), Русский (Russian), Čeština (Czech), 한국어 (Korean), Ελληνικά (Greek), slovenčina (Slovak), română (Romanian), Türkçe (Turkish), Български (Bulgarian), বাংলা (Bengali).

Fritzing Download

It can be downloaded for Windows, Mac or Linux from the official download page or download the version 0.8.7B directly from:

Download Fritzing 0.8.7b for Windows
Download Fritzing 0.8.7b for Mac OS
Download Fritzing 0.8.7b for Linux 

Installing Fritzing

Please make sure your system satisfies one of these requirements:
Windows 10
Windows 7 was reported to work, too
Mac – OSX 10.14 and up, though 10.13 might work too. MacOS 10.15 is currently untested.
Linux – a fairly recent linux distro with libc >= 2.6

  1. Start downloading the Fritzing package that’s right for you.
  2. Unzip your Fritzing folder somewhere convenient on your hard drive.
    • This may also be a good time for you to create a shortcut to the Fritzing application.
  3. To start Fritzing:
    • on Windows: double-click fritzing.exe
    • on Mac: double-click the Fritzing application
    • on Linux: double-click Fritzing, or try ./Fritzing in your shell window
  4. If you experience problems, please try downloading again. This often helps. If it doesn’t, have a look at our forums.
Mac notes

Recent versions of OS X do not allow “unverified” software to be launched directly. In order to run Fritzing, you will need to either:

  1. right-click the Fritzing icon and select “Open”
  2. in the warning dialog, click “Open”

or, to get rid of the warning permanently:

  1. go to the System Preferences
  2. open the Security & Privacy page
  3. unlock it by clicking the lock in the lower left corner
  4. set it to allow app downloads from anywhere
Linux notes

The Linux Ubuntu release has been built and tested under Ubuntu Bionic (18.04).
Fritzing requires the Qt5 libaries. On Ubuntu, those can be installed with “sudo apt install libqt5printsupport5 libqt5xml5 libqt5sql5 libqt5serialport5 libqt5sql5-sqlite”.
The Linux Fedora 30 release has been build and tested under Linux Fedora 30.

Dark Detector using LDR and 555 Timer IC

Darkness detector is simply a LDR (Light Dependent Resistor) interfaced square wave generator. In this project the square wave generator is developed as a 555 Timer IC based ASTABLE MULTIVIBRATOR. As this circuit is primarily based on the working principle of LDR, before going any further to understand this LDR circuit, we must get the basic details of the LDR. The figure below shows an image of various types of LDR.

What is LDR?

LDRs are made from semiconductor materials to enable them to have their light sensitive properties. There are many types but one material is popular and it is cadmium sulphide (CdS). These LDRs or PHOTO REISTORS works on the principle of “Photo Conductivity”. Now what this principle says is , whenever light falls on the surface of the LDR (in this case) the conductance of the element increases or in other words the resistance of the LDR falls when the light falls on the surface of the LDR. This property of the decrease in resistance for the LDR is achieved because it is a property of semiconductor material used on the surface.

Here in this dark detector circuit, LDR is configured with 555 ASTABLE in such a way that 555 ASTABLE generates square wave when the light intensity goes below a certain level.

Circuit Components

  • +5 to +10 supply voltage
  • 555 IC
  • 100KΩ resistor
  • 22KΩ resistor
  • 10KΩ resistor
  • 1MΩ pot or variable resistor
  • 104(100nF) capacitor
  • 2N3906 transistor
  • LDR(any size)
  • Speaker (25Ω,0.5WATT) or any other speaker.

Circuit Diagram

Above figure shows the circuit diagram of dark detector alarm. After some observation the circuit should seem very similar to the ASTABLE MULTIVIBRATOR, that is because the circuit is a ASTABLE MULTIVIBRATOR with only one modification. This modification is done at RESET pin (PIN4). In a normal ASTABLE vibrator this pin is connected to +5V, but since in this case we are supposed to generate pulse on the condition of absence of light it is not connected directly to +5v. The resistor network provided at the RESET pin provides a virtual ground so to keep resetting the IC and so the square wave output is stopped in the presence of light.

The transistor here drives the speaker because the speaker driven by IC is not a good idea. The speaker here can be replaced with LEDs to create an output response of lighting. So once the LEDs are placed and the darkness falls we will have an emergency backup light. The transistor here need not be a PNP compulsory but one can replace it with a NPN and the pin connections should be connected accordingly.


Before going to explanation, the circuit should be assumed ON and is not buzzing in the presence of light. This condition of non-buzzing in the presence of light can be achieved by adjusting the 1MΩ trim pot. Now in the circuit one can observe a voltage divider with 1M, 100K on one side and LDR on the other, the reset pin is connected in the middle. The trimmer pot is said to be adjusted because to create enough resistance on the top branch of voltage divider to drop almost  all the potential (+5v)  in the top branch itself. This leaves a virtual ground at the middle of divider (reset pin). Since the RESET pin of 555 is a LOW LEVEL triggered, the timer IC will be reset mode continuously and so there will be no square wave output as it should be. From this we can conclude that in the presence of light the 555 IC will be in complete reset and provides no output.

Now when the darkness falls on the LDR, the resistance of the LDR increases drastically as explained in introduction, this increase of resistance in the second branch (one with LDR) of voltage divider will be enough to change the ratio of voltage sharing between the two branches of voltage divider section. Once this happen, the potential at the junction of voltage divider circuit rises from 0V to 2V (approximately). And similarly the voltage at the RESET pin rises. This rise of voltage will be enough to lift the 555IC from reset mode. Once this reset mode is lifted, the timer generates square wave output. So it is concluded that once the darkness falls on the LDR the square wave output is generated by the timer.

The square wave generated by the timer is fed to the PNP transistor to drive the speaker. So the speaker outputs sound in response to the square wave.

Common Errors

Even after adjusting the trim pot the buzzing do not stop.

  • The LDR might have enough resistance to put a potential at the reset pin. Put another 100KΩ resistor in series with 1MΩ pot.
  • Check if the RESET pin (PIN4) is accidentally connected to +5V rail in any way.

There is no buzzing even in the dark.

  • LDR might not be developing enough potential at the reset pin. Put a pot in series with LDR and adjust it to get buzzing.

The transistor is getting hot.

  • Drive the signal of 555 troughs the 100Ω resistor to the base of transistor.

3.7v Battery Low Full Indicator Circuit

In This Project 3.7v Battery Low Full Indicator Circuit, We Are Going To Make A Very Simple Battery Level Indicator. This Indicator Circuit Is For A 3.7 Volts Indicator. We Have Designed This Circuit With Few Components At Home With Easily Available Components. These Components Can Either Be Collected From An Old Circuit Or Can Be Purchased From An Electronics Shop Easily.

Components required for 3.7v battery level indicator

  • Transistor – BC547 X1
  • Resistor – 1K X2
  • Resistor – 220 Ohms X3
  • PN-Junction Diode – 1N4007 X1
  • LED – 3V X2 (Red For Low Charge Indication And Green For Full Charge Indication)
  • Battery – 3.7V And 3V

Step 1.

First, Connect 1K Resistor To Base And Emitter Pin Of The Transistor As Shown In The Picture Given Below.

Step 2.

In Second Stop Solder 220-Ohm Resistor To The Collector Pin Of The Transistor As Shown In The Picture.

Step 3.

In This Step Connect 1 Kilo-Ohm Resistor With The Second Point Of The 220-Ohm Resistor.

Step 4.

In Step 4 Connect  Diode IN4007 With The Base Point Of Transistor As We Have Connected In The Picture Given Below. Connect The Cathode Point Of Diode With The Base Point Of The Transistor.

Step 5.

Connect – Point Of Green Led With Diode – Point And +Ve Point Of LED Green Led With 1k Resistor As Shown Below.

Step 6.

Solder – Point Of Red LED To -Ve Point Of The Diode And + Point Of Red LED With Collector Point Of The Transistor As We Have Shown In The Diagram Given Below.

When You Will Connect 3 V Battery Then Red LED Will Glow Completely If The Battery Will Be Low. Green Led Glows When The Battery Will Be Charged Above 3.2V.

Its Tested Circuit Its Complete

15W+15W Dual bridge amplifier Designed by using TDA7297 IC Circuit diagram

15W+15W Dual bridge amplifier Designed by using TDA7297 IC

15W+15W Dual bridge amplifier and it is most suitable for low power car audio amplifier.  This amplifier IC accepts wide range of supply voltage from 6V to 18V. It produce good audio output with minimum external components hence board size becomes tiny.

This IC has stand by and mute functions and it can be handled through microprocessor. TDA 7297 contains short circuit protection and thermal overload protection.

Audio amplifier circuit diagram using TDA 7297 is given from its datasheet. In this circuit IN1 and IN2 are represents stereo Audio input and a potentiometer can be connected through these pins to control sound volume level. Connect two separate speakers with right polarity to get good sound output