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Automatic Night Lamp

WithMorning Alarm.

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Introduction :

This circuit automatically turns on a night lamp when bedroom light is

switched off. The lamp remains on until the light sensor senses daylightin the morning. A yellow LED is used as the night lamp. It gives bright

and cool light in the room. When the sensor detects the daylight in the

morning, a melodious morning alarm sounds.

The circuit utilises light-dependant resistors (LDRs) for sensing darkness

and light in the room. The circuit is designed around the popular timer IC

NE555 , which is configured as a monostable. NE555 is activated by a

low pulse applied to its trigger pin 2. Once triggered, output pin 3 of

NE555 goes high and remains in that position until until timer istriggered again at its pin 2. The musical tone of the alarm is generated by

UM66 IC. The circuit can be easily assembled on a general purpose

PCB. Enclose it in a good-quality plastic case with provisions for LDR

and LED. Use a reflective holder for LED to get a spotlight effect for

reading. Place LDRs away from the LED, preferably on the backside of

the case, to avoid unnecessary illumination. The speaker should be small

so as to make the gadget compact.

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Components used:

IC NE555N

LIGHT DEPENDENT RESISTOR

MUSIC GENERATOR UM66

8, 4.5W SPEAKER

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RESISTORS 220, 560, 580, 1k, 120k, 150k

LIGHT EMITTING DIODE

ZENER DIODE

TRANSISTOR BC548

CAPACITOR 0.01F

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Theory:

NE555 Timer :

General Description:

The LM555 is a highly stable device for generating accurate time delays

or oscillation. Additional terminals are provided for triggering or

resetting if desired. In the time delay mode of operation, the time is

precisely controlled by one external

resistor and capacitor. For astable operation as an oscillator,

the free running frequency and duty cycle are accurately controlled withtwo external resistors and one capacitor. The

circuit may be triggered and reset on falling waveforms, and

the output circuit can source or sink up to 200mA or drive TTL circuits.

Features:

Direct replacement for SE555/NE555

Timing from microseconds through hours

Operates in both astable and monostable modes

Adjustable duty cycle

Output can source or sink 200 mA

Output and supply TTL compatible

Temperature stability better than 0.005% per C

Normally on and normally off output

Available in 8-pin MSOP package

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Pin Diagram:

MONOSTABLE OPERATIONIn this mode of operation, the timer functions as a one-shot. The external

capacitor is initially held discharged by a transistor inside the timer.

Upon application of a negative trigger pulse of less than 1/3 VCC to pin

2, the flip-flop is set which both releases the short circuit across the

capacitor and drives the output high. The voltage across the capacitor

then increases exponentially for a period of t = 1.1 RA C, at the end of

which time the voltage equals 2/3 VCC. The comparator then resets the

flip-flop which in turn discharges the capacitor and drives the output toits low state. Since the charge and the threshold level of the comparator

are both directly proportional to supply voltage, the timing interval is

independent of supply.

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Monostable Mode

Waveforms generated in this mode of

operation.

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MUSIC GENERATOR UM66 :

General Description:

UM66 is a pleasing music generator IC which works on a supply voltage

of 3V. the required 3V supply is given through a zener regulator. its out

put is taken from the pin no1 and is given to a push pull amplifier to

drive the low impedance lowd speker. A clss A amplifier before pushpull

amplifier can be used to decrese the noise and improve out put. UM66 is

a 3 pin IC pakage just looks like a BC 547 transistor.

Features:

62 Note ROM Memory

Voltage rating: 1.3V to 3.3 V

Power on reset

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Pin Diagram:

PIN DESCRIPTION:

Pin No Designation Description

1 Out put Emitter

2 +Vcc Base

3 -Vcc Collector

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Light Dependent Resistor :

A light dependent resistor or photo resistor is a resistorwhose resistance

decreases with increasing incident light intensity. It can also be

referenced as a photoconductor. A photoresistor is made of a high

resistance semiconductor. If light falling on the device is of high enough

frequency,photons absorbed by the semiconductor give bound electrons

enough energy to jump into the conduction band. The resulting free

electron conduct electricity, thereby lowering resistance.

Photoresistors come in many different types. Inexpensive cadmium

sulfide cells can be found in many consumer items such as camera light

meters, street lights, clock radios, alarms, and outdoor clocks.

http://en.wikipedia.org/wiki/Resistorhttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Photonhttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Conduction_bandhttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Cadmium_sulfidehttp://en.wikipedia.org/wiki/Cadmium_sulfidehttp://en.wikipedia.org/wiki/Alarmhttp://en.wikipedia.org/wiki/Resistorhttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Photonhttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Conduction_bandhttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Cadmium_sulfidehttp://en.wikipedia.org/wiki/Cadmium_sulfidehttp://en.wikipedia.org/wiki/Alarm

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PIN DIAGRAM OF TRANSISTORS:

BC548:

FEATURES

Low current (max. 100 mA)

Low voltage (max. 65 V).

APPLICATIONS

General purpose switching and amplification.

DESCRIPTIONNPN transistor in a TO-92; SOT54 plastic package.

PNP complements: BC558.

PIN DESCRIPTION1 emitter

2 base

3 collector

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WORKING:

Circuit Diagram:

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DESCRIPTION:

This circuit automatically turns on a night lamp when bedroom light is

switched off. The lamp remains on until the light sensor senses daylightin the morning. A super-bright white LED is used as the night lamp. It

gives bright and cool light in the room. When the sensor detects the

daylight in the morning, a melodious morning alarm sounds.

The circuit is powered from a 6V DC supply. The circuit utilises light-

dependant resistors (LDRs) for sensing darkness and light in the room.

The resistance of LDR is very high in darkness, which reduces to

minimum when LDR is fully illuminated. LDR1 detects darkness, while

LDR2 detects light in the morning. The circuit is designed around theopular timer IC NE555 (IC2), which is configured as a monostable. IC2

is activated by a low pulse applied to its trigger pin 2. Once triggered,

output pin 3 of IC2 goes high and remains in that position until IC2 is

triggered again at its pin 2. When LDR1 is illuminated with ambient light

in the room, its resistance remains low, which keeps trigger pin 2 of IC2

at a positive potential. As a result, output pin 3 of IC2 goes low and the

white LED remains off. As the illumination of LDR1s sensitive window

reduces, the resistance of the device increases. In total darkness, thespecified LDR has a resistance in excess of 280 kiloohms. When the

resistance of LDR1 increases, a short pulse is applied to trigger pin 2 of

IC2 via resistor R2 (150 kiloohms). This activates the monostable and its

output goes high, causing the white LED to glow. Low-value capacitor

C2 maintains the monostable for continuous operation, eliminating the

timer effect. By increasing the value of C2, the on time of the white

LED can be adjusted to a predetermined time. LDR2 and associated

components generate the morning alarm at dawn. LDR2 detects the

ambient light in the room at sunrise and its resistance gradually falls andtransistor T1 starts conducting. When T1 conducts, melody-generator IC

UM66 (IC3) gets supply voltage from the emitter of T1 and it starts

producing the melody. The musical tone generated by IC3 is amplified

by single-transistor amplifier T2. Resistor R7 limits the current to IC3

and zener diode ZD limits the voltage to a safer level of 3.3 volts.

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The circuit can be easily assembled on a general-purpose PCB. Enclose it

in a good-quality plastic case with provisions for LDR and LED. Use a

reflective holder for white LED to get a spotlight effect for reading.

Place LDRs away from the white LED, preferably on the backside of thecase, to avoid unnecessary illumination. The speaker should be small so

as to make the gadget compact.