System for selectively transmitting messages to passers-by

摘要

A system having several transmitters at fixed locations, such as in a supermarket, and a mobile receiver installed in each push-cart. Whenever a push-cart comes within the range of a transmitter, an exclusive link is set up therebetween for relaying to the receiver an audio message prerecorded in the transmitter for the push-cart user to hear. The receivers beam each "listening" control signals within a predetermined range, in response to which a transmitter within the range of one such receiver relays back a "sending" control signal and sends its prerecorded message which the receiver tunes into. The control signals are single-frequency signals modulating infrared carriers. The message signals are recorded preferably in analog solid-state memories and frequency-modulating radio or infrared carriers in different embodiments. Other uses include public galleries and museums, where one such receiver may be carried by the user instead of installing in a cart.