MAKE YOUR FIRST LIGHT DETECTOR

LIGHT DETECTOR Circuit

This circuit detects light falling on the Photo-cell (Light Dependent Resistor) to turn on the 555 and create a tone that is delivered to the speaker. Pin 4 must be held below 0.7v to turn the 555 off. Any voltage above 0.7v will activate the circuit. The adjustable sensitivity control is needed to set the level at which the circuit is activated.  When the sensitivity pot is turned so that it has the lowest resistance (as shown in red), a large amount of light must be detected by the LDR for its resistance to be low. This produces a voltage-divider made up of the LDR and 4k7 resistor. As the resistance of the LDR decreases, the voltage across the 4k7 increases and the circuit is activated. 

When the sensitivity control is taken to the 0v rail, its resistance increases and this effectively adds resistance to the 4k7. The lower-part of the voltage-divider now has a larger resistance and this is in series with the LDR. Less light is needed on the LDR for it to raise the voltage on pin 4 to turn the 555 on. 

 
SOURCE : http://www.555-timer-circuits.com/light-detector.html

MAKE YOUR FIRST AUTOMATIC CURTAIN CLOSER

AUTOMATIC CURTAIN CLOSER Circuit

This circuit uses a mixture of transistors, an IC and a relay and is used to automatically open and close a pair of curtains. Using switch S3 also allows manual control, allowing curtains to be left only partially open or closed. The circuit controls a motor that is attached to a simple pulley mechanism, to move the curtains. 

Automatic Operation
The circuit can be broken into three main parts; a bi-stable latch, a timer and a reversing circuit. Toggle switch S3 determines manual or automatic mode. The circuit as shown above is drawn in the automatic position and operation is as follows. The bi-stable is built around Q1 and Q2 and associated circuitry and controls relay A/2. S1 is used to open the curtains and S2 to close the curtains. At power on, a brief positive pulse is applied to the base of Q2 via C2. Q2 will be on, and activate relay A/2.
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MAKE YOUR OWN AMPLIFIER AT HOME

The 555 can be used as an amplifier. It operates very similar to pulse-width modulation. The component values cause the 555 to oscillate at approx 66kHz and the speaker does not respond to this high frequency.  Instead it responds to the average CD value of the modulated output and demonstrates the concept of pulse-width modulation. The chip gets very hot and is only for brief demonstrations. 

source : www.555-timer-circuits.com/

MAKE YOUR OWN MOBILE CHARGER

MAKE YOUR OWN MOBILE CHARGER

While travelling charging of mobile battery is great problem because power supply source is not generally accessible. Here is a simple project using very common electronics components for charging mobile battery using AA cells.

Circuit descriptions of mobile cellphone charger

The main part of the circuit mobile cellphone charger is timer IC NE555, used to charge and monitor the voltage level. IC₁ get control voltage to pin 5 by zener diode ZD₁­. Threshold pin 6 and trigger pin 2 is supplied with a voltage set by VR₁ and VR₂ respectively. The trigger pin 2 of IC₁ is below 1/3V_CC when discharge battery is connected to the circuit as a result flip-flop of IC₁ is switched on to take output pin 3 high. The process is reversed when battery is fully charged of charged battery is connected. Here transistor T₁ used to enhance the charging current from output pin 3 of IC₁. Adjust potentiometer VR₁ and VR₂ as per require.

LED status for different charging conditions

Load across the output	Output frequency (at pin 3)	LED1
No battery connected	765 kHz	On
Charging battery	4.5 Hz	Blink
Fully charged battery	0	Off

 PARTS LIST

Resistors (all ¼-watt, ± 5% Carbon)

R₁ = 390 Ω

R₂ = 680 Ω

R₃ = 39 Ω/1W

R₄ = 27 KΩ

R₅ = 47 KΩ

R₆ = 3.3 KΩ

R₇ = 100 Ω/1W

VR₁, VR₂ = 20 KΩ

Capacitors

C₁ = 0.001 µF (ceramic disc)

C₂ = 0.01 µF (ceramic disc)

C₃ = 4.7 µF/25V (Electrolytic )

Semiconductors

IC₁ = NE555 timer IC

T₁ = SL100 or any Medium power general purpose NPN transistor like: 2N4922 , 2N4921,2N4238, FCX1053A

ZD₁ = 5.6 V/1W

LED₁

Miscellaneous

SW₁ = On/off switch

1.5V*8 AA cell

..Read more http://electronicsproject.org/mobile-cellphone-charger/