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I already ask this question in yahoo and in Microsoft........they say that : did I mean to say how to convert analog signals to digital signals.....and they suggest me the theory of AD converter So, here is my question : the electricity that we use in our daily life to operate computers, refrigerators, televisions etc = ANALOG SIGNAL ?......because I want to know how this electricity is converted into digital signals

1. if electricity = analog signal, then ok I already got the answer(AD converter)

  1. if electricity analog signal, then suggest me any book where from I learn this mechanism step by step to convert it to digital signals
  2. if electricity analog signal, can I convert this electricity directly to digital, without converting it first to analog signal
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  • \$\begingroup\$ The opposite question has already been asked, and the answers might help you out: electronics.stackexchange.com/questions/25075/… \$\endgroup\$ – The Photon Jun 13 '14 at 4:56
  • \$\begingroup\$ Everything is analogue (including digital) and both signals are electrical in nature. If I said the voltage is 10.3 volts then I am using base 10 and I can convert this to base 2 (binary) or any base I want to. \$\endgroup\$ – Andy aka Jun 13 '14 at 10:16
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Your question assumes that there are somehow two kinds of electricity, analog and digital. This is not the case. The difference between analog and digital is how we humans interpret an electrical signal. Electricity is electricity, it does not care how we interpret it.

For an analog signal we interpret its level value (voltage, or sometimes current) as conveying information with infinite resolution: in the ideal world 1.00000 Volt and 1.00001 Volt convey different information (the latter could mean for instance that the measured temperature is 0.1 degree higher).

For a digital signal we interpret its level as conveying just one bit of information. For instance, below 2.5V (but ideally 0V) it conveys a 0, above 2.5V (ideally 5V) it conveys a 1.

An analog signal can clearly convey much more information with just the level on one wire. A digital signal on the other hand has the very important property that a little noise on the line does not affect the information in an ideal signal: 0V (ideal 0 signal level) + 1V noise => 1V, which is still recognizable as a 0 level. This means that a digital signal can be transported, stored/retrieved and processed without loss of information.

It turns out that it is much easier and cheaper to create a digital circuit that handle/store/transmit let's say 20 bits (which together can represent ~ 1*10^6 different values) than to create an analog circuit that can do things with an analog signal with an accuracy of 1*10-6. Hence the trend to do everything digital.

That brings us back to your question of A/D conversion. Our real world is inherently analog, and so are (nearly?) all our sensors that interface with the real world. They produce an analog signal, which we would like to feed into our digital circuits. The circuit that does this is called an Analog-to-Digital-Converter. IIRC there are good explanations on SE of the working of an ADC.

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  • \$\begingroup\$ Am I miss-interpreting your statement about 20 bits representing 10^6 different values? 20 bits can actually represent 2^20 different values. \$\endgroup\$ – sherrellbc Jun 13 '14 at 17:29
  • \$\begingroup\$ And 2^20 is approximately .... \$\endgroup\$ – Wouter van Ooijen Jun 13 '14 at 18:27
  • \$\begingroup\$ Right, I know the numbers are approximately the same but it would be just the same to to say 2^20. At least it's more intuitive. \$\endgroup\$ – sherrellbc Jun 13 '14 at 19:08
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    \$\begingroup\$ Not in an analog context. I compare (the information content of) 20 bits to an analog signal that is accurate to 1x10-6 . \$\endgroup\$ – Wouter van Ooijen Jun 13 '14 at 21:08
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if the analog level is higher than some reference point (usually a proportion of the supply voltage of whatever processor/integrated circuit is using the digital signal), it is considered 'digital high', when the analog level gets too low, it is considered 'digital low'. It is merely comparison points, of what should be seen as high and low levels for a digital system. This could be implemented easily with Op-amps used as comparators, with voltage dividers from the supply rail as reference.

You can get low voltage digital systems, whose 'high' signal is not actually high enough for other systems to also say that it's 'high'. That is because they might have different comparison levels, or very different voltage supply levels.

A->D Converters do not tell you "digital high" or "digital low" they tell you in 'steps' how big the analog signal is detected - like 2V might be represented by the A->D Converter as '200', and 3V could be '300' etc. That is of course very dependant on the analog reference voltage, the converter IC, the resolution of the output (8, 10, 12 bits etc) which tells you the number of steps that the detected analog signal can be broken up into and read by something.

"Power" systems can be seen as "Analog" because they are varying in all their interesting properties - there is no one standard for 'powered' and 'not powered' haha!

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All the signals in nature are analog signals. It needs enormous storage capacity to store an analog signal completely. So instead of storing all the values, only samples of a signal are stored and these samples can have only predefined values. The value of samples are 'rounded' to nearest 'allowed' value. Such a representation of signal is called digital signal and these predefined set of 'allowed' values are represented by binary values (combination of 1's and 0's).

The electricity that we use in our daily life to operate computers, refrigerators, televisions is an analog signal. The output of a micro-phone is an analog signal. The ADC's are used to represent these signals with binary values.

Note: Since only samples are taken and values are represented with discrete levels, analog-to-digital conversion leads to loss of some finer details in the signal. But the conversion is usually done with such a precision that the loss of details is under allowed limits or beyond human perception limits.

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The ADC stuff is useful if you want to describe the signal you receive. If you know you are receiving a numerical signal, and expect it to be 0 or 1, you have much more efficient ways to know if your signal is 0 or 1.

You probably know the logical 1 is often 5V, and the 0 0V. Those values depends on the technology you use (most parts on high-end microprocessors now use 1.2V as 1, and 0V as 0), but I will always say "5V" in my answer, for readability.

Were does it comes from ? From transistors. Digital electronics uses transistors as commutators. Transistors either let the current pass, or block it. If you put 5V on the gate of your transistor, it let the current pass, if you put 0V, it blocks the current (some transistors works just the opposite way, some are just different, but it does not matter here). By using 5V in your whole circuit, you become able to switch transistors ON and OFF using other transistors.

So, why precisely 5V ? In fact, we don't really need 5V. 4.5V works fine too, 5.5V works fines too, but 10V will probably make your transistor burn, while 2V will make your transistor let some current pass, but resist to it. On the first case, you destroy your circuit, it is obvious it won't work. On the second case, you just can't predict if your output will allow to put the following transistor to either 0 or 1. This lead to logical issues, such as your processor making a subtraction instead of an addition.

To sum up, we need binary logic, and we make electronics behave as logical systems. We have just chosen some parts of the analog characteristics that allow us to do logic, and avoid to make transistors be between passing and blocking state, as it makes no sense in binary logic.

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I think the aspect that you trying to understand, and most people don't think about, is what is meant by "analog" or "Analogue"?

It really means "analogous" -> adjective (often analogous to) comparable in certain respects.

This means it is a representative in electrical terms (voltage, current) of a real world "signal". If you are designing a sound system you don't actually work with sound, you use a transducer (a microphone) to convert to an electrical signal, manipulate it in the electrical domain and then convert it back when you need to hear it this is done through another transducer (a speaker).

The distinction in the electrical domain is whether the signal is continuous or discrete. the former, confusingly is simply called "analog" in common usage, and the later is called digital, again in common usage.

There are systems, relatively rare now, that use pneumatics to control pneumatic systems, and in some cases those had discrete control ("digital") and continuous control. They are air controlling air, with no "analogous" step in between. Automobiles use mechanical systems to control mechanical systems (springs, shock absorbers etc.).

In some cases you can directly convert from the real world signal (sound, light etc.) directly in the digital domain (discrete electrical signalling). Simple examples might be a contact closure that is temperature sensitive to control a furnace (power on off), to more complex, like an image sensor that detects individual photons and counts them (at that level you could consider light to be in discrete units already - since the term is so loosely applied - you could consider it to be digital already).

Here is a write up on why the distinction between analog and digital is perhaps not significant is certain areas. It's just simply "what is the easiest representation that allows a problems to be solved"

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