Книга: Introduction to Microprocessors and Microcontrollers

Data transmission

The most basic way of sending information from one place to another is simply to connect a wire to both ends of the system and apply a voltage to one end. By making the voltage vary, we can send different levels and even speech or music. These are called analogue signals and have many drawbacks.

The main one is the effect of noise. As the signal travels along a wire it gets weaker and it has noise induced into it by random electromagnetic signals and vibration of the molecules of the conductor. The overall effect is that the signal becomes degraded and weaker.

The ‘weaker’ bit is no problem, we can soon amplify it back to its original size but the noise is a different matter. The electrical noise has become embedded into the signal and has permanently distorted it. Amplifying it will amplify the noise and the signal equally.

We have no problem with digital signals since we know that they will all be rectangular in shape and so the amplifier can be used to regenerate the shape of the signal and hence strip out the effects of the noise. If we are faced with sending something inherently analogue, like speech or music, our first job is to convert it to a digital form.

Оглавление книги