Digital transmission apparatus particularly adapted for security systems

Abstract

A digital transmission system comprises a transmitter and a receiver for use in a security system. An alarm code is set by means of switches in both the transmitter and receiver and is indicative of the address or location of a monitored location. The location as monitored contains a sensor which is in either an opened or a closed condition indicative of a secure or unsecure status. The transmitter operates to transmit a digital code for each change in the status of the loop. The code contains bits which define the alarm code or address, while additional bits define the loop status as opened or closed in conjunction with the condition of a battery which is used to power the transmitter. The receiver is adapted to receive the transmitted signal and is operative to compare the transmitted address with the code stored or programmed by the receiver switches. If a valid code is received within a predetermined interval, the receiver operates to decode the loop status by means of an updown counter. If the loop has been opened and closed the same number of times, the updown counter will indicate a secure position at the end of the day. The receiver also contains circuitry to monitor the battery status as transmitted within the code and to sound an alarm if the battery condition falls below an acceptable value. Due to the large number of possible code combinations and due to the modulation scheme employed, the system provides discrimination between other transmission systems operating within the area.