Audio Spectrum Analyzer free download

File name Audio Spectrum Analyzer(En).pdf

Circuit Design Project Page 1 PART I: INTRODUCE BLOCK DIAGRAM AND OPERATION THEORY I. Basic block diagram of audio spectrum analyzer: 1. Block diagram: Input Filter 1 VU-LED Circuit Filter 2 Display (n circuits) Filter n Basic block diagram of audio spectrum analyzer 2. Operation theory: Input signal comes into each filters. Filters are band pass filters. They only pass signals belonged to fixed frequency range and remove others. We can use transistor and discrete capacitors and resistors to make active filters or we can use OP-AMP and other passive device. The more filters, the higher frequency resolution of spectrum analyzer, shown as the higher quality of the circuit. VU-LED Circuit employed to display signal level behind filters. This kind of display circuit can be discrete devices or specific ICs. The more outputs, the higher resolution of amplitude. In the above diagram, we know that each filter needs and VU-LED circuit for display, the more filters (the higher frequency resolution of the circuit), the more VU-LED circuits. This matter will make the circuit complex for wiring. To overcome this weak point, we will consider following improvement in those block diagrams: Circuit Design Project Page 2 II. Block diagram of audio spectrum analyser uses multiplex display: 1. Block diagram: Input Filter 1 Switching circuit VU-LED Circuit Filter 2 Display matrix . Filter n Oscillator Counter& decoder Driver Block diagram of audio spectrum analyser uses multiplex display 2. Operation theory: The advantage of this diagram is only one VU-LED circuit employed, regardless the number of filters, the number of wiring to display circuit is also more simple because display matrix is the combination of rows & columns. The number of columns is adapted to the number of filters, and the number of rows is the number of VU-LED outputs. This diagram also includes n filters, outputs of the filters are connected to switching circuit, at one time, switch passes signal from only one filter. Switch is controlled by counter & decoder, clocking signal from oscillator comes to conter & decoder, the number of outputs of counter & decoder is n. Ouputs of counter &decoder are also connected to driving circuit to scan columns. If the frequency of clock is fast enogh then our eyes are cheated to have the feeling that all columns are bright simultaneously but actually, at one time, only one column is bright. Circuit Design Project Page 3 PART II: FILTERS I. Introduce filters: Generally, in electronic equipment, if they need to reject or pass any frequencies they often use freqency filters. At first, it's mainly contructed by inductor L and capacitor C. Nowaday, OP AMP with small dimension, many characteristic, low cost, simple in design calculation so it's prefered to make active filter RC. There are many kinds of filters such as Butterworth and Chebyshev. Before consider filters, we must consider filter orders. The order of a filter idenfifies its cuttoff sl