EMBEDDED SYSTEMS RELATED TOPICS



**POWERING THE HARDWARE



First of all what is a power?

ans:power is the rate that energy is expended or work is performed.

This means that in the alternating current(AC) and direct current(DC) circuits, the power associated with each element on the board equals the current through the element and voltage across the element(P=VI).



You all know that every electronic circuit requires power.Lets know about what an embedded system requires.



Accurate power and energy calculations must be done for all elements on an embedded board to determine the power consumption requirements of that particular board.This is because each element can only handle certain type of power, so AC-DC converters,DC-AC,direct AC-AC converters, and so on may be required.

Also, each element has a limited amount of power that it requires to function,that it can handle, or that it dissipates.These calculations determine the type of voltage source that can be used on a board and how powerful the voltage source needs to be.



In embedded systems,both AC and DC voltage sources are used because each current generation technique has its pros and corns.AC is easier to generate in large amounts using generators driven by turbines turned by everything form wind to water. Producing large amounts of DC from electrochemical cells(batteries) is not as practical.Also, because transmitting current over long transmission lines results in a significant loss of energy due to the resistance of the wire, most modern electric company facilities transmit electricity to outlets in AC current, since AC can be transformed to lower or higher voltages much more easily than DC.With AC a device called a transformer, located at the service provider, is used to efficiently transmit current over longer distances with lower losses.

The transformer is a device that transfers electrical energy from one circuit to another and can make changes to the current and voltage during the transfer.

The service provider transmits lower levels of current at a higher voltage rate from the power plant, and then a transformer at the customer site decreases the voltages to value required. On the flip side, at very high voltages, wires offer less resistance to Dc than AC, thus making DC more efficient to transmit than AC over very large distances.



Some embedded boards integrate or plug into power supplies. Power supplies can be either AC or DC. To use an AC power supply to supply power to components using only DC, AC-DC converters can be used to convert AC to lower DC voltages required by the various components on an embedded board, which typically require 3.3, 5,0r 12 volts.

Other embedded boards or components on a board such as non volatile memory rely on batteries as voltage sources, which can be more practical to provide power because of their size.

Battery-powered boards don't rely on a power plant for energy, and they allow portability of embedded devices that don't need to be plugged into an outlet. Also because batteries supply DC current, as is needed with boards that rely on a power supply and outlet supplying AC. Batteries, however, have a limited life and must be either recharged or replaced.




Analog vs Digital Signals



A digital system processes only digital data, which is data represented by only 0's and 1's. On most boards, two voltages represent "0" and "1", since all data is represented as some combination of 1's and 0's. No voltage (0 volts) is referred to as ground, VSS , or low and 3,5, or 12 volts are commonly referred to as VCC, VDD, or high. All signals within the system are one of the two voltages or are transitioning to one of the two voltages.

Systems can define "0" as LOW and "1" as HIGH, on some range of o-1 as LOW and 4-5 volts as HIGH for instance.Other signals can base the definition of a "1" or "0" on edges (low to high) or (high to low). Because most of the components on an embedded board, such as processors, inherently process the 1's and 0's of digital signals, a lot of embbeded hardware is digital by nature. However an embedded can still process analog signals, which are continuous-that is not only 1's and 0's but values in between as well. Obviously, a mechanism is needed on a board to covert analog signals to digital signals. An analog signal is digitalized  by sampling process, and the resulting digtal data can be translated back into a voltage "wave" that mirrors the original analog waveform.



One of the most serious problems in both the analog and digital signal realm involves noise distorting incoming signals, thus corrupting and affecting the accuracy of the data. Noise is generally any unwanted signal alteration from an input source, any part of input signal generated from the sensor other than a sensor, or even the noise generated from the sensor itself. Noise is a common problem with analog signals. Digital signal on the other hand, are at greater risk if the signals are not generated ocally to the embedded processor, so any digital signals coming coming across a longer transmission medium are more susceptible to noise problems.



Analog noise can come from a wide variety of sources- radio signals, lightning, power line, the microprocessor, or the analog sensing electronics themselves. The same is true for digital noise, which can come from mechanical contacts used as computer inputs, dirty slip rings that transmit power/data, limits in accuracy/dependability of input source, and so forth.