The security system application and program offers a simple demonstration of the BASIC Serial Interface. By adding only a few door and window switches, a transistor, a siren, (see schematic) and a few lines of BASIC program (see program listing) the interface can become a multi-function security system.
Normally closed door and window switches can be attached to the interface “in” ports as shown in the schematic(all unused ports should be grounded). In this configuration with all the switches closed the “in” port is held “low”. When any switch opens the port goes “high”. The program recognizes this as an alarm condition for the zone associated with that port. If the program “detects” a high on “in” port number 1 it will delay sounding the alarm for a user defined length of time. This is done to allow the owner time to enter the secured area and reset the alarm before the siren is activated. If a “high” condition is detected on any of the other ports, 2 to 7, an alarm will be sounded immediately.
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