Automatic Emergency Light Circuit Diagram

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.

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 dividerarrangement 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 +V_cc. For this reason the output pin-3 goes low. The base voltage of transistor BC547 is less than 0.75 volt. The transistor is OFF state. So the light is OFF.

In dark position the LDR resistance increase is high so the voltage of the trigger pin-2 decrease to less than 1/3 of +V_cc. The output pin-3 goes high so the base voltage of the transistor BC547 is greater than 0.75 volt. The transistor is ON state. So the light is ON and it emits light.

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LED Emergency Light Circuit Using Boost Converter

The following circuit uses a very common voltage boost converter concept for making a group of white LEDs illuminate at relatively lower power supplies. Lets learn how to make this interesting and useful little LED boost emergency light circuit.


Yet again we take the help of the evergreen work horse, the IC555 for implementing the proposed actions. The figure shows a very simple circuit configuration where the IC 555 has been rigged as an astable multivibrator.
In an astable multivibrator design the various components are wired such that the output generates trains of pulses which are self sustaining and keeps coming as long as the circuit remains powered.

In the present configuration the output of the IC which is the pin #3 generates pulses at a frequency determined by the resistors R1 and R2 and also the capacitor C2.
R2 may be typically adjusted or made variable type for enabling dimming control of the LEDs. However here the value of R2 has been fixed for acquiring optimum brightness from the LEDs.

The pulses available at pin#3 of the IC is used for ddriving the transistor T1 which in turn switches in response to the positive pulses.

The switching of the transistor pulls the supply voltage through the inductor in a pulsed mode.
As we know when alternating or pulsed voltage is applied across an inductor it tries to oppose the current and in the process kick an equivalent high voltage for compensating the applied current force.
This action of the inductor is what constitutes the boost action, where the voltage is stepped to higher levels than the actual supply voltage.
The above functioning of the inductor has been exploited in this circuit also. L1 boosts the voltage in an attempt to restrict the applied AC, this high voltage generated across the coil during the non conducting phases of the transistor is fed across a series connected LEDs for illuminating them under lower current levels. This process helps to illuminate the LEDs at relatively lower power consumption.

L1 winding is not so critical, it is a matter of little experimentation, the number of turns, wire guage, the diameter of the core, all are directly involved and affect the boost levels, therefore must be optimized carefully.
In the prototype I had used 50 turns of 22 SWG over an ordinary ferrite rod, which is normally used in small MW radio receivers.

The LEDs used by me were 1 watt, 350 mA types, howver you may use different types if you want.

Parts List

R1 = 100K
R2 = 39K,
R3 = 100 Ohms,
C1 = 680pF,
C2 = 0.01uF
L1 = see text
IC = LM555
LEDs = as per preference.

PLEASE CONNECT A 10 OHM RESISTOR IN SERIES WITH THE LED CHAIN FOR SAFEGUARDING IT FROM HIGH BOOSTED VOLTAGE.

INCREASING THE VALUE OF R2 SHOULD INCREASE THE BRIGHTNESS OF THE LEDs AND VICE VERSA.

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