Door voice/call-response unit for announcing presence of occupant to a visitor allows the visitor to leave a message or to talk to the occupant on the telephone

摘要

Single-chip micro-controller software continuously compares a frequency spectrum for all noises arising through a microphone (4) with a frequency spectrum for a ring stored once earlier. If this ring is recognized, a pin (12) draws up so that it corresponds to lifting off a door voice unit's live handset and produces a connection with the outer unit.