HOW TO CONVERT 9V TO 3.3 V

In most of the practical applications we need to power our devices which requires smaller voltages. For example to power UM 66 we require 3V and if we apply 5 V or 9V through battery then UM 66 gets damaged. This is just the example of one type of component which requires small voltage. there are various devices available in the market. so to power these devices we require ZENER DIODE . The circuit diagram of the ZENER DIODE as a voltage regulator is shown below.

TO KNOW HOW TO CALCULATE RESISTANCE USED AND MORE ABOUT ZENER DIODE READ ZENER DIODE AS A VOLTAGE REGULATOR 

PEROVKSITE A NEW MATERIAL IN DESIGNING SOLAR CELLS

Researchers at NANYANG technical university , Singapore have successfully developed a new material that can be used to make cheap solar cells. one can estimate the drop in price of solar cells by the fact that the manufacturing cost of perovksite is five times less than the current solar cell materials. the material is so useful in the fact that it can successfully convert the light into electricity by day and emits light at night. now a days solar cells are widely used in power generation replacing the other ways of power generation. with the development of such a wonderful material the solar power would be available at low price.

why RS232 have a (distinct) logic? Why won't it communicate a 5V(TTL high)?

 "RS232 voltage level is different from TTL level.The RS-232 standard defines the voltage levels that correspond to logical one and logical zero levels. Valid signals are plus or minus 3 to 25 volts. minus 3 to plus 3 voltage range is undefined.The range near zero volts is not a valid RS-232 level; logic one is defined as a negative voltage, the signal condition is called marking, and has the functional significance of OFF. Logic zero is positive, the signal condition is spacing, and has the function ON.
The most commonly used RS-232 level converter is MAX232. This IC includes charge pump which can generate RS232 voltage levels (-10V and +10V) from 5V power supply which is required to convert a TTL signal in to RS232 level. The TTL signal is very small in comparison to RS232 level thus we can not directly connect a TTL device with RS232 device as it may damage the TTL device with high level voltage of RS232."

VESTIGIAL SIDE BAND

Vestigial side-band (VSB) is a type of amplitude modulation (AM) technique (sometimes called VSB-AM) that encodes data by varying the amplitude of a single carrier frequency. Portions of one of the redundant side-bands are removed to form a vestigial side-band signal; so it is called Vestigial Wideband Modulation and the portion is called Vestige.

Instead of transmitting only one side-band as SSB, VSB modulation transmits a partially suppressed side-band and a vestige of the other side-band.

The following are the drawbacks of SSB signal generation:

1. Generation of an SSB signal is difficult.

2. Selective filtering is to be done to get the original signal back.

3. Phase shifter should be exactly tuned to 90⁰.

To overcome these drawbacks, VSB modulation is used. It can be viewed as a compromise between SSB and DSB-SC.

PASSIVE INFRARED SENSOR

PiR sensor stands for passive infrared motion sensor. It is based on pyro electric effect that is, it converts heat into electrical energy. It detects the motion of human body and any other living thing which generates the heat. This property of pir is used for detecting the living body and interfacing this module with the micro-controller. The pir sensor has 3.3V output when it senses any body and 0V when there is no motion nearby. It has a good range of 2-7 meters depending on the module and the temperature conditions.

Why a 104(0.1uF) cap to be connected in parallel with DC motors when connected to a uC via any line driver?

When a DC motor runs, the commutator touches the brushes momentarily very frequently which generates a high frequency noise in motor supply. The .1uF capacitor will show a low impedance for this noise and will bypass the this noise. If we do not use this capacitor the noise will travel in DC power supply of uC(micro controller) or any IC and the uC or IC will not function properly and in case of micro controller, restart may occur.

How can AC current pass through the capacitor? There is no connection between charge plates and dielectric. Is it done due to breakdown? How is this possible?"

Alternating charged current arrives at one terminal on the cap. The load to ground is connected at the other terminal of the cap. Actually 'alternating' can be a confusing electrical term to some folks. Think of the charged current as a wave that delivers this positive current from the bottom to the top of the wave and retreats or falls off at the bottom of the other side of the wave. 
This condition is caused from the rotating action of the rotor turning inside the stator fields in a generator. The ground through the load is attracted to the positively charged electrons at the barrier of the cap at the top of the wave from the generator. 
Now, Think charge separation on the ground side. As the electrons become excited on the ground side of the cap at the barrier across from the positive charge (attraction), a vacancy of non-charged electrons has occurred downstream at ground. When the positive charge and current falls at the bottom of the wave from the generator side, the excited electrons at the barrier of the cap on the ground side are now positive (charge separation) and move to power the load and fill the vacancy to ground. This is also the reason for the delay of current and charge moving through a cap to ground. A larger barrier equals a longer delay . Nothing but magnetic field attraction between electrons has happened at the cap barrier. 
This is why a DC current cannot move through a cap. It has no wave. If we pulse the DC, we can get it to move through the cap, but at a lower efficiency than AC.