Car radio with electronic theft protection

摘要

The radio has an arrangement for electrically detecting removal of the radio from its installation location. This prevents the operation of the radio for as long as the theft prevention device remains active after the removal of the radio. The arrangement for detecting the removal of the radio has a monitoring circuit which continuously monitors the presence of a connection between the radio and at least one loud speaker. The theft prevention device is activated directly when this connection is interrupted. The monitoring circuit preferably has an arrangement for applying a constant current to the connection between the radio and the loud speaker. It may also have a comparator stage for testing a voltage drop at the connection created by the constant current. When a predetermined voltage threshold is exceeded by the comparator tested voltage, a break in the connection is detected.