Alarm

PIC CONTROLLED INTRUDER ALARM
JOHN BECKER
A sophisticated multi-zone intruder detection system that offers deluxe monitoring facilities.
Alarm Outputs Four audio/visual alarm control outputs are provided, three via pins RE0-RE2, and one via RB5. When activated, these pins go high and are specifically intended for driving an internal buzzer (RE0), external strobe (RE1), external bell (RE2) andany device of the user’s choice (RB5). As will be discussed in relation to Fig.3, the outputs can activate these devices (depending on their type) either directly, or via power transistors TR1 to TR4. In any alarm condition, the bell, strobe (if fitted) and buzzer are all activated. The bell remains active for a period preset (and automatically stored) by the user through the software, with amaximum duration of 20 minutes. The software prevents the bell from restarting again, irrespective of further unauthorised zone entries (but see Panic Switches later). Once activated, the alarm system can (normally – also see later) only be reset by keying in the correct PIN code. Display A liquid crystal display (l.c.d.) module, X2, is controlled via pins RA0-RA5 operated in output mode. Pin RA4 isan opencollector output and is biased high to the +5V power line via resistor R2. The l.c.d. displays a variety of messages in respect of the several control and status modes that can be selected via the pushbutton keypad(s). It is used in conventional 4-bit control mode and its contrast is adjustable via preset VR1. Keypad(s) The main control of the system is accessed via a standard 16-keyalphanumeric “data entry” keypad, S1, through which a unique 4-digit alphanumeric personal identity (PIN) code has to be keyed. There are 28560 permutations (134 – 1). The status of the keypad’s pushbutton keys is monitored via port pins RC4-RC7 used in output mode, and RB0-RB3 used in input mode. Port B’s internal “light pullups” are activated in the software and additional biasing resistors for RB0-RB3are not needed. Facilities for the use of an optional second 16-key keypad, S2, are provided, for reasons discussed later. Four of its pins share pins RC4-RC7 with keypad S1. The others are monitored by pins RD4-RD7 used in input mode, with logic-high biasing provided by resistors R3 to R6.

Constructional Project

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Editor Mike suggested that the author might be interested in designing aPIC controlled intruder alarm, the suggestion was accepted in the knowledge that to do the job properly would make a worthwhile challenge. The author has designed alarms before but none having the sophistication that appeared possible through using a PIC microcontroller. It seemed that an ideal system should have the features itemised in Panel 1. It is believed that all the requirements listed inthe Panel have been met in this design. How they are implemented will be discussed as we progress.
HEN

Everything else follows on from this logical argument but, as is illustrated through Panel 1, there are many factors that make a considerable difference between a 1-gate circuit that simply detects an open-closed condition and a system that provides a great many other security aidingfacilities as well (there are around 1900 program commands in the controlling software for this design).

CIRCUIT DIAGRAM

The main circuit diagram for the PIC Controlled Intruder Alarm is shown in Fig.1. The principal functions are as follows: Main Zones PIC16F877 microcontroller IC1 is in charge of the entire system. Via port pins RD0-RD3 and RC0-RC3, which are used in input mode, the PIC canmonitor between one and eight sensor zones, plus an extra “Panic” zone via RB4. The quantity is selected by the user and can be changed at any time. Zone detection will be discussed shortly.

Designing an intruder alarm system is based on the simple Boolean logic concept that a sensor’s switch contacts can be either open or closed. If the contacts are found to be in the opposite condition to that in...