| 摘要 |
An intercommunication system for transmitting signals through a door, and having piezo transducer devices mountable on each side of the door, a matrix of analog switches connecting the piezo transducer devices to the input and output of a bridge amplifier, and a TALK switching device which controls which piezo transducer device is connected to the bridge amplifier through the analog switches as a speaker or as a microphone.
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