Elenco Computer Inteface for Snap Circuits&reg Manuel d'utilisateur télécharger pdf (Page 55)

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Project #PC65

Siren PC

OBJECTIVE: To view the output of a fading siren circuit.

Build the circuit and try the settings shown. Flip on the slide switch

and press the press switch for a few seconds and release. View

the waveform as a siren starts up and then slowly fades away.

Settings

Note: Although the amplitude of the pulses appears to be varying

across the screen (the wider time scale shown below shows this

better), this is an illusion caused by the way Winscope measures

the signal. The amplitude of the pulses is not really varying.

Winscope makes measurements using a 44kHz sampling rate,

which is fast enough to measure the frequency of this signal

(varying from 1-5kHz). However these pulses have much of their

energy spread among higher frequencies that approach the

sampling rate (see the sample spectrum plots at right), where the

amplitude measurement becomes increasingly inaccurate.

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Elenco Computer Inteface for Snap Circuits&reg Manuel d'utilisateur Page 55