electronic projects

9 V regulator using 7809 Description. H ere is the circuit diagram of 9 V regulator using popular 7809 IC. The 7809 is a 9 Volt voltage regulator IC with features such as internal current limit, safe area protection, thermal protection etc. A 16 V transformer brings down the 230V mains, 1A bridge rectifier rectifies it and capacitor C1 filters it and 7809 regulates it to produce a steady9V DC  output. Circuit diagram with Parts list.  Notes.  If a current of 300 mA or above is required, fit a proper heat sink to the IC 7809. If 1A bridge is not available, make one using four 1N 4007 diodes.

Battery charger circuit using SCR  Description. 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 smal...

Air flow detector circuit Description. This circuit can give a visual indication of the rate of air flow.It can be also used to check whether there is air flow in a given space. The filament of a incandescent bulb is the sensing part of the circuit.When there is no air flow the resistance of the filament will be low.When there is air flow the resistance drops , because the moving air will remove some of the heat generated in the filament.This variations in the resistance will produce variation of voltage across the filament.These variations will be picked up by the opamp (LM339) and the brightness of the LED at its output will be varied proportionally to the airflow. Circuit diagram with Parts list. Notes. The filament L1 can be made by removing  the glass of a 40W incandescent bulb. The circuit can be powered from a 12 V DC power supply.

Water level alarm circuit Description. Here is a simple water level alarm circuit using 555 timer that will produce an audible alarm when the water level reaches  a preset level.The circuit can be powered of a  3V battery and is very handy to use. The circuit is based on an astable multivibrator wired around IC1 (NE 555).The operating frequency of the astable multivibrator here will depend on capacitor C1, resistances R1,R2 and the resistance across the probes A&B.When there is no water up to the probes,they will be open and so the multivibrator will not produce oscillations and the buzzer will not beep.When there is water up to the level of probes,some current will pass through the water,the circuit will be closed to some extend,and the IC will start producing oscillations in a frequency  proportional to the value of C1,R1,R2 and the resistance of water across the probes.The buzzer will beep to indicate the presence of water up to the level of the sensing pr...

Low cost fire alarm circuit. Description. W hen there is a fire breakout in the room the temperature increases. This ultra compact and low cost fire alarm senses fire breakout based on this fact. Transistor BC177 (Q1) is used as the fire sensor here. When the temperature increases the leakage current of this transistor also increases. The circuit is designed so that when there is an increase in the leakage current of Q1, transistor Q2 will get biased. As a result when there is a fire breakout the transistor Q2 will be on. The emitter of Q2 (BC 108) is connected to the base of Q3(AC 128). So when Q2 is ON Q3 will be also ON. The transistor Q3 drives the relay which is used to drive the load ie,light,bell,horn etc as an indication of the fire. The diode D1 is used as a free wheeling diode to protect it from back EMF generated when relay is switched. Do you need to get a better understanding on the basics of electronics? We have listed 4 of the best books to learn the basics of...

Single Chip FM Radio circuit Description. Here is a compact low cost  FM radio circuit  using IC TDA 7000. This circuit is designed as per the data sheet and the result is excellent.Ideal for all category of electronic enthusiasts. The TDA7000 is a monolithic integrated circuit for mono  FM portable radios,  where a minimum on peripheral components is crucial. The IC TDA 7000 has a Frequency-Locked-Loop system with an intermediate frequency of 70 kHz. The intermediate frequency selectivity is achieved by active RC filters. The only function which needs alignment is the resonant circuit for the oscillator, thus selecting the reception frequency. Spurious reception is avoided by means of a mute circuit, which also eliminates too noisy input signals. Special steps are taken to meet the radiation requirements. FM Radio Circuit Diagram with Parts List.  Notes For L1 and L2 wind 5 turns of 0.6 mm enameled Copper wire on a 4 mm dia plastic former. For a...

Automatic Washroom Light Switch We turn On the lights in our washroom when we enter it and turn them off when we leave. We sometimes forget to turn Off the lights after leaving the washroom. This may lead to power wastage and also the lifetime of the lights may decrease. To avoid these problems, we are going to make a circuit which automatically turns On the lights when a person enters the washroom and it automatically turns it Off when he leaves it. By automating this, there are many advantages like, the person need not care to turn On the light always when he is using the washroom. The circuit which we are doing does it automatically for that person. Also, the person need not turn it off after using the washroom. There is no fear that he forgets to turn it Off. The circuit is also designed to consume lesser power so that the circuit can be used in any household or public washrooms without worrying about the power bills. Automatic Washroom Light Switch Circuit Diagram: The ...

Auto Night Lamp Using High Power LED Auto Night Lamp Using High Power LEDs is a circuit which turns ON the LED lights interfaced to it at night time and it turns OFF the lights automatically when it is day. Usage of LEDs is growing day by day due to the advantages they provide compared to the conventional filament bulbs or fluorescent lamps. They provide good quality of white light with a better intensity compared to others. They also consume less power compared to their alternatives. These are the advantages which the LEDs encourage us to use them compared to their alternatives. In this article, we shall see the circuit and the working of turning on or off of high power LEDs with light intensity. The element which is used for sensing light in the circuit is the light dependent resistor. The resistance of the light dependent resistor depends on the light incident on it. If the intensity of light incident on it is more, then the resistance of the circuit decreases. If the intensi...

Water Level Alarm Using 555 Timer How many times did your overhead water tank overflows due to your forgetfulness? It is a frequent problem in all homes where people turn ON the water pump and forget to turn it off when the water is filled. This project is made to solve this problem. Also Read the Interesting Post –  Water Level Controller Circuit using 8051 Microcontroller. In this project, we are using a water level alarm using simple and low cost hardware using a 555 timer circuit. The aim of this project is to make a water level detecting alarm with simple and low cost hardware without compromising on the performance of the device. Water Level Alarm Using 555 Timer Circuit Diagram: Circuit Diagram of Water Level Alarm using 555 Timer  The circuit uses a 555 timer in astable mode with R1=220 ohms, R2= 150 ohms and C1=1 uF. As we know, the frequency of operation of the IC 555 in astable mode depends on the values of R1, R2 and C1. By calculating the ...

Metal Detector Circuit Introduction: Metal detector is very common devices for checking the person in shopping malls, hotels, cinema halls to ensure that person is not carrying any explosive metals or illegal things like guns, bombs etc. metal detectors can be created easily and the circuit is not that complex. Block Diagram of Metal Detector: The LC circuit is nothing but inductor and capacitor which is connecter in parallel. The LC circuit will trigger the proximity sensor if it detects any metal near to it. Proximity sensor will give glow the led, and also make the buzz with the help of the buzzer. Main Components in Metal Detector Circuit: LC CIRCUIT:  LC Circuit is a resonating circuit which will resonate when exact same frequency material comes near. The LC circuit consist of inductor and capacitor connected in parallel , when the capacitor is fully charged the charge of the capacitor will be given to the inductor, here inductor will have improve its magnetic...

Fire Alarm with Siren Sound Fire Alarm Circuit: This circuit alerts us when there is a fire accident at home by ringing a siren sound. You might have seen fire alarms earlier but this is quite different as it generates a siren sound instead of a buzzer and also it uses basic components to generate that siren sound. We are aware that there are many integrated circuits which can be used to generate the siren effect but we preferred to use basic electronics components like resistors, capacitors and transistors to generate it so that you will clearly understand the internal working of it and it will be much useful for you as you will gain more knowledge by analyzing it instead of simply going or pre designed integrated circuits. Circuit Diagram of Fire Alarm: Description: This circuit uses a thermistor to sense the temperature. When it senses that the temperature of the environment is increasing above a given threshold, then it gives a signal. The temperature at which the ci...

Intelligent Unambiguous Night Lamp Switcher We usually turn ON the lights in our houses and offices manually. We need to turn ON the lights only when it is dark. So, how will that be if we make a circuit which turns ON the lights automatically when it is dark? In this circuit, we shall see how to make a circuit which turns ON our domestic lights automatically when it is dark. While making a   Night Lamp Switcher , there are many aspects which needs to be taken into consideration without which there is a possibility of destroying the home appliances and lights. In this circuit, strict measures are taken to ensure that the lights to be operated are not damaged because of switching. In general, if we make a simple automatic night lamp switcher, it may turn ON the lights when it is dark. But here comes a problem. When the level of darkness is approaching, the circuit may get successive signals of dark and light with little time intervals. This may cause the circuit to repeatedly...

Simple LED Blinking Circuits LED (Light Emitting Diode) is a semiconductor light emitting diode. We know that diode allows the current in one direction and does not allow the reverse current which will affect the components in the circuit. LED also do the same function but will emit a small light when it allowed the current, which will give the sign or visual indication to the normal human that circuit is working. There are lots of applications using LEDs. They are mainly used for visual indication in any electronic devices, measuring and interacting with the process, displaying the pictures in TV or in any advertisement hoarding, etc. Related Post –  Bipolar LED Driver Circuit Two LED blinking circuits are given below. First one is dancing bi-color LEDs (two different color LEDs) where the two color LED will run in sequence. In the second circuit, we will blink the LEDs in regular period of time. Dancing Bi – Color LED Circuit: Generally we use small voltage bulbs i...

Thermistor Temperature Sensing Alarm This circuit is a temperature sensing as well as alarm circuit. The circuit raises an alarm whenever the temperature crosses a certain limit. Temperature monitoring is a very important and frequently used application in industries and in many other places where the temperature should be kept below a maximum allowable level. This circuit comes to our rescue when a situation of that sort arises. The circuit is made to be low cost and reliable so that you can make it with less resources and without compromising on the performance. Although it is not an industry level calibrated circuit, it is quite sufficient where it is not a mission critical application. Another advantage of this circuit is that the circuit has a flexibility to adjust the temperature level to which it should be set. This means that you can set the temperature above which the circuit should activate the alarm. Circuit Diagram of Thermistor Temperature Sensing Alarm: T...

Cell Phone Detector Circuit The most common electronic equipment used is cell phones. With advancement in communication technology, the requirement of cell phones has increased manifold. A cell phone typically transmits and receives signals in the frequency range of 0.9 to 3GHz. This article provides a simple circuit to detect the presence of an activated cell phone by detecting these signals. Basic Principle of Mobile Phone Detector Circuit: The basic principle behind this circuit is the idea of using a Schottky diode to detect the cell phone signal. Mobile phone signal is in the frequency range of 0.9 to 3GHZ.  Schottky diodes have a unique property of being able to rectify low frequency signals, with low noise rate. When an inductor is placed near the RF signal source, it receives the signal through mutual induction. This signal is rectified by the Schottky diode. This low power signal can be amplified and used to power any indicator like an LED in this case. Also Re...