| 摘要 |
A musical door chime which includes a repertoire of musical tunes one of which is played when a door pushbutton, preferably the front door pushbutton, is actuated. The musical tune which is played may be selected by means of a keyboard connected to a microprocessor. Digitally encoded representations of the notes of each musical tune are stored in a memory. Each digitally encoded musical note is read from memory by the microprocessor and converted by the microprocessor into a squarewave having the frequency and the duration of the note. The microprocessor is connected to a note strike and decay circuit which is preferably connected in series with an active audio filter circuit for translating the squarewave into a sinusoidal output for energizing a loudspeaker so that relatively high quality audible tones are heard when the musical tune is played. Preferably, a two-note musical tune is played when a rear door pushbutton is actuated, and a fixed single musical note is played when a side door pushbutton is actuated. The musical door chime is preferably also combined with a visual display driven by the microprocessor for indicating the time of day. The time is preferably annunciated every quarter hour by means of musical notes. A multi-frequency tone is played for the hour strike. The keyboard serves various other control functions in addition to selecting the musical tune to be played.
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