| 摘要 |
A signal sensing circuit (10) receives an electrical signal on an input (18, 20) to connect power to a controlled device in the presence of an electrical signal and disconnect power in the absense of the electrical signal. The electrical signal is capacitively coupled (28) to an amplifier (30) and low pass filter (32) for amplifying the signal and filtering out high frequency components of the signal thereby eliminating the false triggering by transient noise on the inputs. The signal is rectified (34) and compared (38) to a predetermined set point. When the signal exceeds the set point, a timer (44) is triggered. The timer (44) produces a control signal when triggered for a predetermined time, and can be retriggered by subsequent control signals which resets the predetermined time. The presence of the control signal actuates a switch (48) to supply power to the control device, such as an amplifier.
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