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Analog & Digital Signals February 25, 2012

Posted by peterxu422 in Science, Technology.
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For as long as I can remember, I have heard the terms Analog and Digital signals. In this advanced digital era, the terms have become more ubiquitous than ever. Though I was familiar with their names, I have never quite understood what they actually were or their differences until recently.

An analog signal is a continuous signal that varies with time. Continuous simply means that it is not interrupted. For example, a traditional clock with hands is an analog source. The hands keep moving without interruption and so it shows you EVERY moment of time during the day. A digital signal on the other hand only shows you finite quantities that change with time. A digital clock is, obviously, a digital source. Most only display up to the minutes. As a result, the time does not change continuously, but in steps of minutes. A digital clock that changes from 10:00 to 10:01 only shows you a change in the minute. But what about the seconds in between, or the milliseconds in between, or the nanoseconds in between? An analog clock on the other hand, technically shows you all of these and more, even though our human eyes are unable to detect them.

Another example of an analog signal would be that produced by a microphone. When you speak, your vocal chords cause the surrounding air molecules to vibrate which produce sound. If you hold a microphone close to you and speak into it, the vibration of the air molecules causes a metallic coil inside the microphone to vibrate accordingly. When the coil vibrates, it creates an electrical current that resembles the sound. The current is a continuous varying signal and so it is an analog signal. In technical terms, the current becomes an analog of the sound. This current is then fed to an amplifier and reconverted back into vibration which produces a louder sound.

What has puzzled me most about analog and digital signals is how they can be converted back and forth. Digital signals as we all know are composed of units of information called bits, which are represented by 0’s and 1’s. How then, I wondered, could a simple set of 0’s and 1’s represent something as complicated as a sound signal?

The way it works is as follows. Most analog signals can be converted to electrical currents. These electrical currents change with time and their “strength,” or amplitude, constantly changes as well. If you divide up the signal into sections, at certain points, the current will have a certain amplitude. At one instant it might be 7 Amps, then later on the signal could decrease and become 2 Amps. These values can be represented as binary numbers (number consisting only of 0’s and 1’s). If you do this for many amplitudes, you can essentially represent the entire analog signal in binary. This is the conversion from analog to digital.

In the end, the digital signal needs to be converted back to analog to get the original signal back (remember the microphone?). So you may ask what’s the point of this anyway? Well, the benefit of digital is that it is very useful for transporting data. Analog signals are constantly changing and controlling their amplitudes is difficult. Also, transporting them over long distances makes it more susceptible to signal degradation and quality loss. But with digital, you only need to control two values, 0 and 1, which is basically a no pulse or pulse of current. Since it uses just these two values and nothing in between, it makes it less likely for the signal to degrade. If a pulse of current is sent (1) and during its transport it slightly decreases and becomes say 0.80, on the receiving end it gets rounded to the closest value and becomes a 1 again, thus preserving the signal. This is the reason why digital signals are of such clear and high quality.

Let There Be Light…and Data February 20, 2012

Posted by peterxu422 in Science.
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In my Optoelectronics class this semester, we study how principles in optics are applied to modern day communications technology. My professor pointed out that within a few years there may be a huge market for LED lights. LEDs may be a crucial component in allowing devices to send data between each other within sight.

Most data in this day and age is sent digitally. Digital data is represented by a series of 0’s and 1’s, which can physically represent no current (0) or a pulse of current (1). This is a very good system because a very complicated signal can be represented by just 2 values. Manipulating the order in which they appear determines what kind of signal you send.

Similarly, light can also be used as a binary system. Instead of using a current, it uses on/off light to represent 0’s and 1’s. Therefore, if you have a receiver that can detect these pulses of light, you can send data digitally using light. Imagine embedding these light sending/detecting technologies in mobile devices. It would completely change the way we send information to each other. Instead of sending data through Wifi, it would be through Lifi – Light Fidelity.

Some drawbacks you may notice are for example, that there may be very annoying flickering from the LEDs of devices as they send digital data through Lifi. But light detectors can be sensitive enough to detect slight variations in the brightness of light emitters. As opposed to turning the light completely off to represent a 0, it would just make it slightly less bright than the brightness setting for a 1. These variations would be so small that our human eyes would not be able to perceive them. Instead, what you would probably see is the LED turn on for the duration of the time it is sending the data. Another problem is that you have to be able to physically see the other device or else there is no possible way to send data using light. This is true, but it also offers certain levels of security protection that wifi does not offer. For example, if a hacker wanted to steal the data you were sending through Lifi, he/she would have to physically intercept the light beam somehow. Finally, you may say that if you can only send data, like a text message, to another device within viewing distance, you may as well just walk up to the person and tell them. But of course, this data sending is not limited to text messages by any means. For instance, you can send documents, photos, videos, and essentially any type of data you would send to a computer.

The promise of Lifi and LED communications technology are very great and, in my opinion, incredibly exciting. Watch an incredible TED talk below on Lifi and an awesome demonstration.

Harald Haas: Wireless data from every light bulb

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