Re: DAC and ADC
ADC: Analog to Digital Converter, its a circuit (device) used to convert analog signals to digital ones with a given percision, eg. A 4 bit ADC will convert from 0 - 5 Volts analog to a digital number ranging from 0000 to 1111 depending on your configuration.
DAC: The Opposite, it will convert a digital signal to an analog signal, eg. If I want voltage between 0 and 12 V from a 4 bit ADC, I may configure 1111 to be 12 V, 0000 to be 0 V. You can make one like this using Op-Amps.
Why: ADC's and DAC's are used much in control and data aquisition applications. The problem is, we use DIGITAL computers, we want to deal with ANALOG signals, we need to convert the ANALOG signal to DIGITAL so that the computer can deal with it and process it. The most frequent use is you listening to MP3s and the studios processing digital music, how can they do that? The sound you hear through the speakre is analog, and you need to process it. The analog processing circuits are expensive and are not easy to change, so we use the computer or any digital system, whose processing parameters are easly changed and very flexible. Now, after the processing, we need to listen to it, we don't listen to pulses (try the listening to pulses using the MATLAB, but take care not to destroy your sound card or ears), we only analog signals make sense to us, so we need to convert them back to analog signals.
Hope this one helped, if there is any problem with it or any other thing please let me know