Archive for the ‘Light Related’ Category

Photocell based night light

Description. Many automatic night light circuits had been published here. This one uses a photocell for detecting the light intensity. At full light the resistance of the photocell will be few ten ohms and at darkness it will rise to several hundred ohms. The IC1 uA741 is wired as a comparator here. At darkness the resistance of photocell increases and so the voltage at the inverting input of the IC1 will be less than the reference voltage at the non inverting input. The output of the IC1 goes to positive saturation and it switches ON the transistor to activate the…

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LED ramping circuit.

Description. In this circuit the intensity of LED will vary in a ramping fashion. The circuit consists of three ICs: Two 555 timer ICs and one LM393 op-amp. IC1 and IC2 are wired as oscillators to produce 10 KHz and 1 Hz frequencies respectively.These two frequencies are given to the inputs of the op-amp LM393.LM393 is wired as a comparator and its output will be a PWM signal. This PWM signals controls the FET Q1 to drive the LED. The LED will rise from OFF state to full brightness slowly and then slowly fades to OFF state and this operation…

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Photo relay circuit

Description. A photo relay or light activated relay is a circuit which opens and closes the relay contacts according to the light.Here a photo diode is used to sense the light.The photo diode offers a high resistance when there is no light falling on it.Here the photo diode is connected in reverse biased condition.The only current flowing through it will be due to the minority carriers.When light falls on it, the current due to the minority carriers increase and the diode offers a low resistance.As a result the voltage across the diode will not be sufficient to make the transistor…

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Flashing LED unit

Description. The circuit given here is designed as an LED flasher which produces a rotating effect when the LEDs are arranged properly. The circuit has very low current consumption and can be operated from even 3V button cells. The IC 1 (CMOS NE555) is wired as an astable multivibrator wired at a duty cycle of 50% and 4Hz frequency and drives LEDs D1 to D6.The second IC, IC2 (CMOS NE555) is working as a trigger pulse inverter and drives LEDs D7 to D12.The circuit is arranged such that the ICs sink the current consumed by the LEDs. At low operating…

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How a LED works – Light Emitting Diode working

Watch the video given below to get a better idea on how LED works?  A light emitting diode (LED) is known to be one of the best optoelectronic devices out of the lot. The device is capable of emitting a fairly narrow bandwidth of visible or invisible light when its internal diode junction attains a forward electric current or voltage. The visible lights that an LED emits are usually orange, red, yellow, or green. The invisible light includes the infrared light. The biggest advantage of this device is its high power to light conversion efficiency. That is, the efficiency is…

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Brightness controller for low power lamps.

Description. The circuit given here can be used to control the brightness of low power incandescent lamps. The circuit is based on IC NE555 which is wired as an astable multivibrator with variable duty cycle. The output of IC is connected to the base of transistor Q1.The Q1 drives the lamp. The duty cycle of the multivibrator can be varied by varying the POT R4.As a result, the brightness of the lamp varies according to the position of the POT R4.The same circuit can be also used for speed control of small DC motors. Circuit diagram with Parts list. Notes….

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Puff to OFF LED circuit.

Descrption. This is a simple circuit in which the glowing LED can be switched OFF just by a puff. A condenser mic (M1) is used to sense your puff. When the push button S1 is pressed, the transistors Q2 and Q3 wired as latching pair gets activated and drives the LED to glow. The LED remains in this condition. When you puff on the condenser mic, the sound pressure is converted into a voltage signal at its output. This voltage signal will be amplified by the transistor Q1.Since the collector of the Q1 is coupled to the emitter of the…

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Dark detector circuit

Description. The dark detector circuit shown here can be used to produce an audible alarm when the light inside a room goes OFF. The circuit is build around timer IC NE555. A general purpose LDR is used for sensing the light. When proper light is falling on the LDR its resistance is very low. When there is no light the LDR resistance increases. At this time the IC is triggered and drives the buzzer to produce an alarm sound. If a transistor and relay is connected at the output (pin3) of IC1 instead of the buzzer, electrical appliances can be…

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Micro Flasher

Description. This micro flasher circuit continuously emits flashing light with the consumption of very less power.The circuit can run for a very long time for four 1.5 V torch cells.   Here a low power CMOS IC CD4093 (IC1) is used to produce sharp pulses  of 20 ms from a red LED.The LED appears to be glowing continuously due to persistence of vision ,and lot of power is saved.The IC1 is quad NAND gate whose one gate is used for producing oscillations.The unused inputs are kept to logic 1 by connecting it to the positive.The value of R1 determines the…

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Mini Flasher

Description. Here is a simple and compact flasher circuit that an be used where ever a flashing LED is needed.The circuit finds application in flashing beacons,alarms automobile and more. The circuit is nothing but an astable multivibrator based on IC NE 555 (IC1).The frequency of the oscillation depends on the values of R1,R2 ,R3 and C2.The LED glows when the out put  (pin3)  of IC1 goes high.The  IC1 NE 555 can easily drive a LED.The resistor R4 acts as a current limiter for LED. Circuit diagram with Parts list.  Notes.  A 6V battery or 6V DC power supply can be…

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