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Fire alarm can be made with a light sensor (LDR) as in the article with the title of Fire Alarm with this LDR sensor. Principles of fire detection Fire Alarm with LDR sensor is to detect the presence of smoke through the LDR. LDR in the series Fire Alarm does not stand alone in detecting a fire, but the LDR in the pair with the light shining on the LDR. Hence, in the detected smoke from the fire then the intensity of light received by the LDR LDR decreases and eventually trigger an alarm system on a series of Fire Alarm with this LDR sensor. Part 2 that in the series of Fire Alarm with Sensor LDR are some of the sensors, tone generator, audio power. Image Series Fire Alarm with Sensor LDR Function Section of the Fire Alarm with Sensor LDR Part of LDR and light sensor facing to fire smoke detection Part trigger using transistors and regulators as a trigger tone generator 7805 Tone generator section with IC UM66 Power audio section uses an audio power IC TDA 2002 which is equipped with v...

This is an automatic emergency lamp with day light sensing, means it senses darkness/night and turns ON automatically. Similarly it senses day light and turns OFF automatically. A simple emergency lamp which does not require any special equipment; even a multimeter to assemble and use. Any individual who can do a good quality soldering must be able to build this circuit successfully. This can be easily accommodated in the defunct two 6 watt tube National Emergency Lamp or any PL tube type emergency lamp. The difference will be in the working; it will work non stop for more than 8 hours.deep discharge is taken care by the LED characteristic and over charge protection is taken care by the fixed voltage regulator.This uses a simple 3Pin fixed regulator which has a built in current limiting circuit. The only required adjustment is the preset which has to be set to ensure the LEDs just light up (it should be left at that position). The 5mm LDR is just mounted on top of the emergency light a...

This is Christmas season so you all may get ready to do lots of variations for your house for your gardens.In Christmas Christmas tree gets an important place so I decided to give very important circuit to decorate your Christmas tree here these bulbs are blinking.Moving 1M preset the speed of the bulb can be changed.about 20 bulbs (25w) Can be connected for this circuit.  230 v Christmas Flash Light Circuit Diagram Note # All the resistors must be 1/4w. # When you work with 230 be careful always try to get the assistance of an elder.

This is a very simple electronic circuit project of light sensitive and differential temperature switch circuit.   In Fig. 1 see a precision light- sensitive switch that activates when the sensed quantities go above or below pre-set values. The LDR can be any cadmium – sulfide unit that has a resistance in the range 500R to 20k at the required trip level. The RV1 adjust LDR at normal light level. In Fig. 2 see a differential temperature switch circuit using ordinary silicon diodes as temperature – sensing elements and responding to differentials of a fraction of degree. RV2 can be used to apply an effective offset of several degrees to the two diodes. To adjust the circuit, apply the required differential temperature to the diodes and then adjust RV2 so that the relay just turns on. The circuit responds to the relative temperatures, rather than the absolute temperatures, of the two diodes.

This is the simple circuit of automatic emergency light. It is called dark dependent circuit. A 555 timer IC and LDR is used for this configuration. When light fall on the LDR, its resistance is decrease and in dark position its resistance is going high. Using these characteristics of LDR, automatic emergency light is made. Circuit Diagram : Simple Automatic Emergency Light Circuit Diagram LDR is called Light Dependent Resistor. Its resistance is inversely proportional to the falling light on its surface. In dark, its resistance is approximately 7k to 10k. When light fall on its surface, its resistance is decrease to less than 1k. In the circuit, a voltage divider arrangement circuit is used here with LDR and 10K variable resistor. When light fall on the surface of LDR, the resistance decrease to 1k. So the voltage of the timer pin-6 is greater than 2/3 of +Vcc. For this reason the output pin-3 goes low. The base voltage of transistor BC547 is less than 0.75 volt. The transistor ...

The 555 circuit below is a flashing bicycle light powered with four C,D or AA cells (6 volts). Two sets of 20 LEDs will alternately flash at approximately 4.7 cycles per second using RC values shown (4.7K for R1, 150K for R2 and a 1uF capacitor). Time intervals for the two lamps are about 107 milliseconds (T1, upper LEDs) and 104 milliseconds (T2 lower LEDs). Two transistors are used to provide additional current beyond the 200 mA limit of the 555 timer. A single LED is placed in series with the base of the PNP transistor so that the lower 20 LEDs turn off when the 555 output goes high during the T1 time interval. The high output level of the 555 timer is 1.7 volts less than the supply voltage. Adding the LED increases the forward voltage required for the PNP transistor to about 2.7 volts so that the 1.7 volt difference from supply to the output is insufficient to turn on the transistor. Each LED is supplied with about 20mA of current for a total of 220mA. The circuit should work with ...

Normally, the refrigerator lights  are  yellow in colour  and  go  bad  very  often. If you want a long-lasting white light  for  your  refrigerator, this circuit is especially for you.The circuit is easy to install inside the refrigerator. Also, it consumes very  little power compared to the traditional yellow bulb.   Circuit diagram : White Light For Refrigerator Circuit Diagram   The circuit is transformerless and uses a capacitor for providing the power supply to the white LEDs. Mains input is fed to capacitor C1 and resistor R1, rectified by a bridge rectifier comprising diodes D1 through D4, and filtered by capacitor C2 to provide sufficient voltage to drive the white LEDs. Resistor R2 limits the current flowing through the LEDs. The circuit uses 16 bright white LEDs in 2×8 parallel connection configuration.   Assemble the circuit on a general purpose PCB along with 16 white  LEDs. Connect the LEDs in series with resistor R2. Take out the two wires from the usual bulb connecti...

The light sensor circuit shows the application of  photo diode to detect the presence of light. This light sensor can be used as an intermediate circuit in various applications to detect the presence or absence of light. The sensitivity of the sensor can be adjusted using the preset. A photo diode , used as a photo detector, generates current in the circuit when light incidents on it. This circuit uses the photo diode in reverse bias mode with resistor R1(10k). This resistor does not allow too much current to flow through the photo diode in case a large amount of light falls on the detector. Initially when no light falls on the photo diode, it results in high potential at the inverting input of a comparator (pin6) of LM339. When light falls on the photo diode, it allows current to flow through the diode, and thus drops the voltage across it. The non-inverting input (pin7) is connected to a variable resistor VR2 (preset) which is used to set the reference voltage of the compar...

Description In many cases, the dimmer presented here may be built into a wall-mounted box containing the light switch. It is intended for use with 240 V incandescent lamps only. When it is fitted, and the light is switched on, the lamp does not come on fully for about 400 ms (which is not noticeable). When the light is switched off, it stays on unchanged for about 20 s, and then goes out gradually. This has the advantage that it is not immediately dark when the light is switched off. When light switch S1 is turned on, capacitor C2 is charged via R1, C1 and bridge rectifier D1–D4. Zener diode D5 limits the potential across C2 to about 15 V. After a short while, diode D6 lights, whereupon a potential difference ensues across light sensitive resistor R3, which is sufficient to trigger triac Tr1. Circuit diagram:   The light then comes on. When the light switch is turned off, C2 is discharged via P1, R2 and D6. When the potential across C2 drops, the brightness of the LED diminishes, s...

There have been lot of problems in street lights. Major problem in some places is every evening a person has to come and switch ON the street light and it should be again switched off in morning. Yes, this may not be the situation in everywhere but exists in many places. So this problem can be overcome by using a simple circuit. Below shown circuit will be automatically switched ON and OFF during night and morning times respectively. Circuit diagram : Simple Automatic street light Circuit Diagram In above circuit R1 can be used to adjust the sensitivity. And the working of the circuit is very simple. The LDR will have very low resistance during day time so the transistor Q1 will be in OFF condition. And during night time the resistance will be very high so automatically the transistor Q1 will be ON. The Q1 is PNP transistor and the emitter of Q1 is given to base of Q2. So the Q2 transistor will be ON only if the transistor Q1 is ON. The TRIAC is used in the circuit to make is circ...

Reagarding this circuit sent out an alarm when its LDR sensor is exposed to light by sun or lamp. A 555 astable multivibrator was used here which sent signal a tone of about 1kHz upon detecting light. The sensor when exposed by light completes the circuit and makes the 555 oscillate at about 1kHz with transistor to drive current. The sensor is also shown in the circuit diagram. It has to placed making an angle of about 30 – 45 degrees to the ground.  Sensitivity can be adjust with P1.  This makes the sun light to flow through it to the ground and prevents the alarm from going on due to the stored light on the sensor.

This Simple Emergency Light and Alarm Circuit Diagram is permanently plugged into a mains socket andNI-CD batteries are trickle-charged. When a power outage occurs,the lamp automatically illuminates. Instead of illuminating alamp, an alarm sounder can be chosen.When power supply is restored, the lamp or the alarm isswitched-off. A switch provides a “latch-up” function, in orderto extend lamp or alarm operation even when power is restored.Circuit operation:Mains voltage is reduced to about 12V DC at C2`s terminals, bymeans of the reactance of C1 and the diode bridge (D1-D4). Thusavoids the use of a mains transformer.   Simple Emergency Light and Alarm Circuit Diagram Trickle-charging current for the battery B1 is provided by theseries resistor R3, D5 and the green LED D6 that also monitorsthe presence of mains supply and correct battery charging.Q2 & Q3 form a self-latching pair that start operatingwhen a power outage occurs. In this case, Q1 biasing becomespositive, so this tr...

While living in rent or in hostel the problem like stealing is often in absent time. Here is the circuit of simple and inexpensive sound – operated light to overcome this type of problem which can turn on the light when someone claps, or tries to open your door or even inserts a key in the door lock. The switching of light is alternately i.e. light on by one sound pulse and off by another. It is also called clap operated light or clap switch. The entire circuit of sound operated light is designed and builds around an operational amplifier IC (IC 1 ) and JK flip-flop IC (IC 2 ). The sound coming from outside is senses by microphone and converts it to corresponding electrical signal where sensitivity of sound is controlled by potentiometer VR 1 . The high value of reference voltage is given to pin 3 of IC 1 in order to change the output voltage from pin 6. Here IC 2 (JK flip-flop) is wired as a toggle flip-flop and its output is connected to relay driver transistor T 1 thr...

Circuit diagram of the light-sensitive fire alarm is shown in Fig. 1. It is built around L14F1 photo transistor (T1), BC547 transistor (T2) and NE555 timer (IC1). T1 can sense both infrared and visible light. NE555 based a stable multi vibrator is used for audible warning. Resistors R3 and R4 and capacitor C1 decide the frequency. Here, frequency is around 272Hz, which can be changed by changing values of R3, R4 or C1. When T1 senses light, T2 stops conducting. As a result, reset pin 4 of IC1 is held high. This makes the multivibrator to function and an alarm to sound in loudspeaker LS1. An actual-size, single-side PCB of the light-sensitive fire alarm is shown in Fig. 2 and its component layout in Fig. 3. After assembling the circuit on a PCB, enclose it in a suitable plastic case. Make a small hole in the plastic case for the photo transistor (L14F1) so that fire flame is detected/sensed easily through it. T1 sensor should not face directly towards normal light sources like sunlight,...

This is simple electronic Circuit Diagram Project of Low Light Level Drop Detector. This self-biasing configuration is useful any time srnall changes in light level must be detected, for example, when monitoring very low flow rates by counting drops of fluid. In this bias method, the photodarlington is de bias stabilized by feedback from the collector, compensating for different photodarlington gains and LED outputs. The 10-I`F capacitor integrates the collector voltage feedback, and the 10-MO resistor provides a high base-source impedance to minimize effects on optical performance. Low Light Level Drop Detector Circuit Diagram: The detector drop causes a momentary decrease in light reaching the chip, which causes collector voltage to momentarily rise, generating an output signal. The initial light bias is small because of output power constraints on the LED and mechanical spacing system constraints. The change in light level is a fraction of this initial bias because of stray light pa...

Circuit Diagram:  Description Here is the circuit diagram of IC Controlled Emergancy Light With Charger or simply 12V to 220V AC inverter circuit. The circuit shown here is that of the IC controlled emergency light. Its main features are: automatic switching-on of the light on mains failure and battery charger with over-charge protection. When mains is absent, relay RL2 is in de-energized state, feeding battery supply to inverter section via its N/C contacts and switch S1. The inverter section comprises IC2 (NE555) which is used in stable mode to produce sharp pulses at the rate of 50 Hz for driving the MOSFETs. The output of IC2 is fed to gate of MOSFET (Q4) directly while it is applied to MOSFET (Q3) gate after inversion by transistor Q2. Thus the power amplifier built around MOSFETs Q3 and Q4 functions in push-pull mode. The output across secondary of transformer T2 can easily drive a 230-volt, 20-watt fluorescent tube. In case light is not required to be on during mains failure...

Hi…. friends . I am again here with some discussion on Light Emitting Diodes (LEDs) So in this article we will discuss about function and uses of LED . LED are most basic electronic component to be used in almost all the electronic circuit in different forms. If you are going to start with electronics you must have proper knowledge of using LEDs efficiently. INTRODUCTION ( FUNCTION AND CONNECTION) LEDs are unidirectional devices like diode and works only in forward bias condition and emits light when a power supply is connected across the terminal of LED. There are two terminal in simple LED ( some special LEDs contain more than two terminals).As shown in figure below these two terminal are termed as anode ( represented with a or +) and cathode (represented with k (not c) or -). These two terminals must be connected correct way round as a to positive and k to negative terminal of supply. You can determine ANODE and CATHODE by checking the LED as the larger lead is anode and shorter...

This is an automatic emergency lamp with day light sensing, means it senses darkness/night and turns ON automatically. Similarly it senses day light and turns OFF automatically. A simple emergency lamp which does not require any special equipment; even a multimeter to assemble and use. Any individual who can do a good quality soldering must be able to build this circuit successfully. This can be easily accommodated in the defunct two 6 watt tube National Emergency Lamp or any PL tube type emergency lamp. The difference will be in the working; it will work non stop for more than 8 hours.deep discharge is taken care by the LED characteristic and over charge protection is taken care by the fixed voltage regulator.This uses a simple 3Pin fixed regulator which has a built in current limiting circuit. Simple Emergency Light Circuit Diagram: The only required adjustment is the preset which has to be set to ensure the LEDs just light up (it should be left at that position). The 5mm LDR is just...