Elenco Upgrade Kit SC500 to SC750 - Manual (Page 143)

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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.