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A multi-sector burglar alarm Looking for an up-to-date burglar alarm system that's big on features but low in price? This unit is easy to build & features keypad entry plus microprocessor control to provide a comprehensive array of features. By MIKE ZENERE Within the last two years, there has been a sharp increase in break-ins an d burglaries. While the obvious precautions are a start, th ey really only present a small challenge to a professional thief. An effective alarm unit, however, can be a real deterrent an d will greatly increase th e security of your h ome or business premises. There is now a bewil dering array of alarm systems available to the consumer, ranging from inexpensive units to thousand dollar systems th at h ave a host of features. The un it described in this article in cludes most of the features of the expensive systems but comes at an affordable price (just $195 for th e alarm panel). Main features Because it's based on a microprocessor, this unit includes facilities that are not fo und on other alarm panels in its price range. Table 1 lists the main functions provided by the unit. They include a 4-digit programmable on/off code; three user selectable sectors (ie, each sector can be switched on or off) ; a 24-hour sector input (eg, for m onitoring a smoke detector) ; pro- Table 1 : Main Features . • Three user selectable sectors with LED status indicators. • One 24-hou r sector (for monitoring sm oke alarms, etc) • Resi stive loop sensing; can be used with both normally open (NO) and normal ly closed (NC) switches. • Inbuilt si ren driver circuit. · • Battery back-up plus automatic battery check function . • Variable entry, exit and siren duration times. • Em its warn ing beeps during entry delay pe ri od to remi nd user that the alarm is active. • Automatic loop check of siren and strobe-light lines. · • Visual and aud ible warning of any faults. 56 SI LICO N CHIP • Microprocessor controlled with automatic watchdog ci rcuit to reset unit if prog ra!TI crashes. • Programmable 4-digit on/off code. • Automatic siren lock-out if false tripping continuously occurs. • Siren , strobe light, rel ay and LEDs can be manually tested via keypad. • Optional remote keypads with LED indicators. • All variables programmable from main keypad. • Relay contacts for external circuits. • Incident report facil ity: indicates which sectors have tripped and the number of occasions. • + 12V DC 1.5A output capabi lity for siren and strobe light operation; + 15V DC 400mA rail for sensors. grammable entry, exit and siren duration times; battery back-up; automatic battery test facility; automatic testing of the siren and strobe light lines; optional remote keypads; and the ability to manually test the siren, strobe light and on-board relay. Each ofth e three programmable sectors h as a status LED on both the main box and on the remote keypads. These status LEDs indicate which sectors have been activated. Also , if a sector has been activated but not secured (eg, if a door has been left open), the corresponding sector LEDs flash on and off at th e main box and remote keypads. Note that the sectors cannot be turned on or off once the alarm has been armed . They can only be altered after the alarm has first been disarmed by entering the 4-digit on/off code. In addition to the sector LEDs, the front panel also carries two small LEDs which alternately flash when power is applied, an on/off LED (to show wh ether or n ot the unit is activated), a memory LED which lights if the alarm sounds, a keypad and a 4-character alphanumeric display which flashes the message "UNIT OK" if everything is correct. The display is also used to indicate problems and to indicate settings (eg, the on/ off code and entry and exit periods) w hen the unit is being programmed. Although its versatility might make the unit appear daunting, in practice it is very easy to set up and operate. All settings are entered via the keypad using the number keys, the (function) key and the # (enter) key. For example, to turn sector 1 on or off, you simply enter *1. Sectors 2 and 3 are turned on or off in exactly the same manner (ie, by entering *2 and *3, respectively) . Unlike the programmable sectors, the 24-hour sector cannot be turned off. Nor does it have exit or entry delay times. Instead, this sector is on permanently and is typically used to monitor fire/smoke detectors. Apart from that, each of the four sector circuits is identical and will accept both normally open (NO) and normally closed (NC) switches. Fig.1 shows how an end-of-line resistor is connected in conjunction with both types of detectors. The resistor stops a would-be thief from cutting or shorting out the input cables to the alarm. With this set up , almost any type of intrusion detector can be used. These include passive infrared (PIR) detectors, lightbeam relays, reed switches, pressure mats, window foil strips, and ultrasonic and microwave movement detectors. Because user requirements vary, the 4-digit on/off code and the entry, exit and siren duration times can be altered at any time. The latter settings range from O seconds to about 10 minutes and all settings are stored in an EEPROM. Each time variable is adjustable to the nearest second. Note that you must know the current 4-digit code in order to change any settings, for obvious security reasons. When the alarm starts counting down its entry delay period, the display panel and the remote keypads emit a beeping sound. This has two purposes. First, it reminds the user to switch off the alarm each time he enters the premises before the siren starts screaming. And second, it serves to warn off any intruder by indicating that the alarm siren is about to sound. The unit also incorporates an alarm lockout feature which monitors the number of times that the alarm sounds in one 12-hour period. This is useful if continuous false tripping occurs (eg, due to a faulty sensor) . When the alarm sounds for the first time, the microprocessor (MCU) starts an internal 12-hour timer and counts any further soundings of the alarm. If the total number of soundings in that * · · · ~TOBl Cl S£CTOR2 0 SECTOtl 3 The alarm circuitry is housed in a pre-punched steel case & all commands are entered via the keypad. A 4-character alphanumeric display is used to show the alarm status & to indicate test results & programmable settings. 12-hour period is equal to the set number, then no further alarms take place until the timer has timed out! Remote keypads Up to two remote keypads can be connected to the alarm panel and these would typically be mounted just inside a door. The remote keypads provide sector control and allow the alarm to be armed or disarmed in exactly the same manner as the keypad on the main unit. Unlike the main keypad, however, the remote keypads cannot be used to program in variables or to perform the various test functions. Seven small indicator LEDs are mounted on the remote keypads to indicate the status of the alarm - three at the top and four at the bottom. The top row carries two armed/disarmed indicator LEDs plus the memory LED, while the bottom row carries the three sector LEDs and a fault indicator LED. All keypad entries are accompanied by a beep to confirm that an entry has been made. Self-checking routines There are several se\f-testing routines and any failures are mainly indicated on the alphanumeric display. First, the battery is placed on test once a week and if it fails, the words SEPTEMBER1992 57 "CHEK" and "BATT" alternate on the display. Second, the processor constantly looks for loops in both the siren and strobe light lines and if one or both of these fail, "CHEK SIREN" or "CHEK LITE" is displayed. The remote keypads also inform the user of any faults by flashing a red LED and by making an intermittent beep, once every five seconds. As an added precaution, the board also has a "watchdog" circuit that will reboot the unit if it crashes. All variables are stored in an EEPROM, so that the unit can continue from where it left off. This ensures that the siren doesn't run continuously. Although this circuit has been added as a precaution, the chances of this happening are next to zero as all the address and data lines are internal to the MCU. Battery back-up The alarm panel is backed up by a 12V 2.6Ah battery in case of mains failure. If the mains does fail, the processor senses this and uses two methods to conserve power. First, power to the rem{lte keypads is shut off and all commands must now be entered via the main keypad. Second, approximately 15 seconds after the last keystroke, the display blanks out apart from the two flashing status LEDs. If the user subsequently hits a key after the display goes out, a further 15 seconds of viewing is available. How it works The alarm panel is made up of two PC boards: (1) a main processor board; and (2) a display board. These two boards are connected together via a 16-way data cable terminated at either end with IDC connectors. The remote keypad is built onto a separate PC board and housed in a small plastic case. In addition to the microcontroller, the processor board (see Fig.2) contains a host of smaller circuits which are vital to the running of the alarm. These include the watchdog circuit, an alarm driver, the sector inputs, line loop detectors , relay contact outputs, a battery charge and testing unit, and the transmit and receive components for the remote keypads. At the heart of the alarm panel is the 68 705P3 microcontroller. This device is a complete computer on a chip and controls the entire alarm panel. All of its 20 I/O (input/output) 58 SILICON CHIP 07 INPUT: GND ·>-------------' la) NC SWITCH INPUT u - - - - t > - - - - - - - , 10k GNDu-----t-----~ lb) ND SWITCH 10k GNDO-----t>--------' (c) NO+NC SWITCHES Fig.1: the circuit employs resistive loop sensing so that the sectors can accept both normally open (NO) & normally closed (NC) sensor switches. pins have been used and the program takes up almost all of the internal EPROM. Because the data bus is hidden from the user, port A is used to communicate with the outside world. It is used both to talk to the display board and, when programmed as an input, to receive data from the keypad and sector inputs. Timing for the system is derived from the 50Hz AC input (via bridge rectifier BR1) and this is used as an accurate interrupt for the processor every 20ms. During this time, the display board is updated, the clock is incremented and the system communicates with the remote keypads. Power·supply Power for the unit is provided by a 16VAC plugpack from which all other voltages are derived. The AC voltage is rectified by BR1 and filtered by Cl to produce about Z0VDC. The battery is a 12V 2.6Ah type and is trickle charged via R3, with ZD4 and D17 clamping the voltage to about 13.8V to prevent overcharging. Rl and RZ are used to reduce the power dissipation across REG1 , which provides a +5V rail for the ICs and their associated circuits. The Z0VDC is also fed via RB to REGZ , a 15V regulator used to run the passive infrared detectors and remote keypads. Should the mains fail, DZ and D3 conduct and feed 12V from the battery to both REG1 and the output of REGZ, thus maintaining the system. D16 protects REGZ from reverse voltage during battery operation. Fuses Fl and FZ are included in the 12V outputs to protect the system from overload, while fuse F3 limits the 15V output to approximately 400mA. This . is enough to handle two remote keypads and about seven passive infrared detectors. As mentioned previously, the MCU will shut down power to the remote keypads to conserve battery life if the mains fails. This is accomplished in the following way. When the mains fails, pin 19 (PB7) on the MCU goes low and switches off Ql 1. Ql 1 in turn switches off Q12 and this then switches off the power to the remote keypad circuit. Battery charge & test circuit During normal operation, Ql is turned on and charges the battery via R3. However, once a week the battery is placed on test for a period of one minute and, at the end of this time, its voltage is checked. Let's see how this is accomplished. First, pin 13 (PB1) of the MCU goes low, thus turning offQ3 which in turn switches off Ql. With Ql off, no charging current is applied to the battery. At the same time, Dl becomes reverse biased which means that QZ turns on and so current now flows through R4 and QZ to ground. After about one minute, the voltage across the battery is checked and read by the processor. If the voltage is slightly higher than 9V, ZD3 conducts and current now flows through RZ0 and the base-emitter junction of Q4. Q4 thus turns on and produces a logic "0" on pin 2 of IC3 (a 74HC541 octal Tri-state buffer) which tells the processor that the voltage is OK. Fig.2.(right): the processor board carries the 68705P3 microcontroller (IC1), which forms the heart of the circuit. The processor board also carries the watchdog circuit (IC2e & IC2f); the sector inputs (IC4a-lC4d); the siren driver (IC2a-IC2d & Q10); a battery charge & test circuit ( Q1-Q3); & the transmit & receive components for the remote keypads (Q7 & Q8). J1 8 r-~r-....---~-----,----....-----....---..---.-.,--------..---~ vcc ~GNO R17 68k 20 TB1 SEC 1 vcc +5V i I t----+------+---i--------------"1'1 K86 I r-------+---~--------------"OK85 ov~ j'----------+--------------'OK84 I .,. I I R48 10k I SEC PA7 11 12 IC3 PA6 74HC541 PA 13 5 PA4 14 3 2 PA3 PA2 PA1 .,. R~3 1Qk PAO PA7 PA6 PA5 ! PA4 01J PA1 15 +5V 6 +5V 17 18 C16 PA3 PA2 PAO SEC I 4 4 (24HR) PC2 PC1 OV<Y::i_ I .,. j I SEC PCO V+ R43 10k 6 J I 10 +15Vo!-+15V +12V~+12V 28 201 4.7V +12vo)2..12v 01 5 1N4004 I I +5V-'--+--~ TB2 v------oc1 ~--------------,l----4------- 8 LIGHT·U' I 5 XTAL PA7 27 ~C2 ovo½._ I .,. I I SIREN .,. I 10 18 ' - - - - - - - - - - - - - - - - - - - - - '-"! P86 R64 10k IC1 68705P1 R65 4.7k 17 P85,l-''--- - - - - ' +15V I R62 PITT~1~9-~1NO~k~--~8~ITT1 '-1=PN100 +5V R11 100k I I I I _r-1ov .,. +5V I - - - - < IX I PB3 15 PB1 PM 13 16 016 1N4004 I I I I I +5V +5V I R30 10k I I I V+ +12V 1 r-----e----1-------__:,l-----41'--.,__ __._...r,;_:F'.r>-- +12V P3 12V 2.6AH 1 111 SIDE ECB I pi ~ _...-PLASTIC VIEWED FROM BELOW T ...I... c0E ZD4~ 13V~ BURGLARALARM-PROCESSORBOARD SEPTEM8ER 1992 59 J1 vcc +5V 8 GND~ c1I 1 - C2 +5V + 1r C4 C6 01! 011 LE06 CJ 011 1 -! 9 20 PA7 g PA7 PAS B PA6 PA6 7 PA4 6 PA4 5 PA3 PA3 4 PA2 PA5 15 17 STAT CS 12 13 KB3 14 IC1 KB2 74HC574 KB1 15 LED7 PAO CS PA4 ffi CEZ WR .,. .,. +5V PC2 PC1 PCO 6 CUE GND 10 4 .,. .,. PCO KB6 KBO 11 20 2pA7 ON 3 A6 4 MEM PA5 5 PA4 6 PA3 SEC1 7 2 PA 74~i~74 B PA1 SEC2 g PAO KB4 2 KB5 KB4 CS 01-+ PC1 KB6 cTii DISP1 HPOL2416 1 .,. CUE BL PAS 17 PA4 14 PA3 13 PA2 12 PA1 .,. J PA1 2 PAO PA1 18 voo PA6 16 KBO 16 PA2 + C7 LE01 19 KB1 lB 17 KB3 0 0 80 © 0 KEYPAD1 0 0 4 0 0 ® 60 16 ~- 8EEP1 10 .,.. BURGLAR ALARM - DISPLAY BOARD Fig.3: the display board circuit includes the keypad, an HPDL-2416 4-character alphanumeric display and a 93C46 EEPROM (IC3) which stores the time variables & the current alarm status. IC1 & IC2 are 8-bit latches. IC1 provides the interface between the keyboard rows and the MCU, while IC2 drives LEDs 1-5. thus enabled again and generates another reset pulse for the MCU. Siren driver On the other hand, if the battery voltage is low, then "CHEK BATT" is displayed, while any remote keypads connected show a fault condition and beep every five seconds. The battery is then placed on charge again for one hour and at the end of this time the test is repeated . This process continues until the battery voltage reaches an acceptable level. Watchdog circuit The watchdog circuit consists of an astable oscillator made up of C9, R16 and inverter IC2e, plus an isolation circuit consisting of CB, R14, R15, D9 and IC2f. At power up, voltage divider R14 and R15 ensures that the input to IC2f is low and so its pin 12 output is high. This reverse biases D9 and allows pin 11 of IC2e to be pulled high via C9. 60 SILICON CHIP ICZe's output will thus be low and this low is used to reset the MCU. Pin 10 ofICZe remains low until the oscillator changes state some 400ms later (as set by C9 and R16). When pin 10 of ICZe goes high, the processor comes out of reset and begins normal execution. During normal operation, an interrupt occurs every Z0ms and this causes pin 9 (PC1) of the MCU to pulse high, then low. This pulse is passed through CB and causes pin 12 of ICZf to pulse low. Pin 11 of ICZe thus remains low (since C9 never has sufficient time to discharge) and so pin 10 of IC2e remains high for as long as this pulsing process continues. However, if the program crashes, the pulses from pin 9 of the MCU cease and pin 12 ofIC2fremains high. The as table oscillator based on IC2e is The siren driver consists of two oscillators, one modulating the other to obtain the desired effect. The first oscillator is based on IC2a and has tw o feedback circuits, one via R37 and the other via D13 and R38 in series. These feedback components give an output waveform with a low duty cycle and a frequency of just a few Hertz. This waveform is then fed to an RC coupling network based on R39 and C21 and the resulting sawtooth waveform then fed to oscillator stage ICZb via R40. As a result, IC2b produces an output signal that changes in frequency to give a siren effect. During normal operation, the siren will be off. That's because pin 12 (PB0) of the MCU is held low and thus pin 3 . of IC2b is also held low (via Dl0), thereby disabling the oscillator. DlO provides isolation between the two circuits, while ZD2 ensures that the voltage applied to pin 12 of the MCU cannot exceed 4. 7V. When the alarm is to be sounded, pin 12 of the MCU goes high and reverse biases D10. IC2b now oscillates and drives power transistor Q10 via parallel buffer stages IC2c and IC2d. Q10 then drives the siren. Interrupt circuit The MCU runs an interrupt routine 50 times a second to produce the necessary timing for its internal counters. This interrupt is derived from the 50Hz AC signal. The waveform is taken from one side of bridge rectifier BRl and is current limited by Rl3. Diodes D5-8 clip the peak to peak voltage to a safe level, while C6 provides DC blocking. C7 is there to filter unwanted spikes. The resultant waveform is applied to the interrupt input of the MCU (pin 2) and produces an accurate and reliable signal to keep the system in sync. Transmit/receive circuits The transmit and receive circuits are used to communicate with the remote keypads (if any are connected to the system). They use only a few parts, since most of the work is done by the software. When a logic "1" is to be sent, PB3 (pin 15) on the main MCU goes low and turns off Q7. Current now flows through R29 and along the Tx line to the remote keypads. Conversely, when a logic "0" is to be sent, PB3 goes high and turns on Q7 which pulls the Tx line low. Input stages A 12V 2.6Ah SLA battery provides back-up for the alarm in the event of a mains failure. To conserve the battery in this situation, the circuit automatically shuts offthe power to the remote keypads & turns off the alphanumeric display after a 15-second delay. The display can be re-activated at any time by pressing a key. If the input now goes open circuit, pin 8 of IC4d will rise towards Vee, while pin 9 will rise to about 2/3Vcc. This now represents a logic "1" on both inputs of the XOR gate and so its pin 10 output goes low (ie, an intrusion has been detected). On the other hand , if the input is short circuited, pin 9 will be pulled low while pin 8 will fall to 1/3Vcc. As before, this causes the pin 10 output to go low. The outputs of the four input sectors are all fed to IC3 and, at the appropriate time, latched through to the MCU. The input stages are used to link the MCU to the outside world. All four sectors are capable of connecting to both normally open and normally closed switches at the same time. This . Loop detectors The loop detectors are used to sense is made possible by the 10kQ end of line resistor associated with each sec- whether or not the fuses, siren lines and strobe light lines are all intact. tor input. Because all input stages are This feature enables the alarm to warn the same , we'll just consider input 1. the user that all is not right. Under The heart of the circuit is a 4070 normal conditions , with the unit in quad exclusive OR (XOR) gate (IC4). the standby mode , the driver transisUnder normal conditions, with the tor for the strobe light (Q9) will be off, line terminated by the 10kQ resistor, the junction ofR59 and R60 is held at thus presenting an open circuit to any 1/2Vcc. Thus, pins 8 and 9 ofIC4d are voltage that appears on its collector. If both the fuse and the line are held at 1/3Vcc and 2/3Vcc respecintact, then 12V (applied via the light tively, and so the output of the gate (pin 10) is high. C29 and C30 filter out filament) will be present at the junction ofR23 and R24 , and so Q5 will be any noise that may appear on the line. off. However, if the line or the fuse goes open circuit, then Q5 turns on and applies a logic 1 to PB6 (pin 6) of the MCU which then signals a fault. Display board The display board is used to show the status of the alarm unit at a single glance. It uses four ICs, three of which appear as latches to the MCU. Two of these (IC1 and IC2) are in fact 8-bit latches, while the third is a Hewlett Packard 4-character alphanumeric display (HPDL-2416) which is used to indicate time variables and any faults with the system. This device contains a 4-word ASCII memory, a 64-word character generator, four 17-segment drivers and the clocking circuitry. There are 10 lines of interest: PA0PA6, CS and two address lines (Al and A2) . .IC1 provides the interface between the keyboard rows and the MCU, and also selects the appropriate digit on the display using lines AO and Al. The ASCII code is presented to the data lines and then clocked in by taking CS low. The remaining chip on the display board is a 93C46 EEPROM (IC3) which holds all of the important data and is SEPTEMBER1992 61 PARTS LIST PP1 - 16VAC 1.5A plugpack W1 - red battery lead, 160mm W2 - black battery lead, 160mm L - link wire, 170mm Batt1 - 12V 2.6Ah SLA battery Screws (Type 1) - M3 x 6mm pan head Pozidriv x 3 Screws (Type 2) - M3 x 12mm countersunk Pozidriv x 4 Screws (Type 3) - M4 x 12mm pan head Pozidriv x 2 Nuts - M3 x 7 Washers - M3 shakeproof x 7 Standoffs - 4 x 6mm untapped GR1 - C.5mm rubber grommet Box1 - steel pre-punched alarm case with adhesive label RC1 - ribbon cable, 16-way x 200mm PVCD1 ,PVCD2 - 4.88mm terminal cover PROCESSOR BOARD PCB1 - BURGPROC.PCB Sckt1 - 28-pin IC socket J1 - 16-way IDC DIP FC1 ,FC2,FC3,FC4,FC5,FC6 M205 fuse clips Fuse 1,2 - M205 1.5A Fuse 3 - M205 400mA RLY1 - reed relay, PCB mount TB1 - 12-way screw terminal block TB2 - 2-way screw terminal block TB3 - 4-way screw terminal block HS1 ,HS2 - heatsink, 30 x 25 x 13mm HS3 - heatsink, 20 x 18 x 9mm P1 ,P2,P3,P4 - PC pins CR1 ,CR2 - 4.8mm female crimp receptacle Semiconductors 01 OA91 02,03,015,016,017 - 1N4004 or equiv. 04,05,D6 ,07,D8,D9,D1 0,D11, D12,D13,D14 - 1N914 or 1N4148 BR1 - WO-2 bridge rectifier ZD1 ,ZD2 - 4.7V zener diode ZD5,ZD6 - 6.8V zener diode ZD3 - 9.1 V zener diode ZD4 - 13V zener diode Xtal1 - 4MHz IC1 - 68705P3 microcontroller IC2 - 74C14 hex Schmitt trigger IC3 - 74HC541 octal tri-state buffer IC4 - 4070 quad XOR gate REG1 - 7805 voltage regulator REG2 - 7815 voltage regulator 01,05,06 - PN200 PNP transistor 62 SILICON CHIP 02 - B0139 NPN transistor 03,04,07,08,011 - PN100 NPN transistor Q.9,O10 - B0681 NPN transistor 012 - B0140 PNP transistor LED1 - 3mm red LED Capacitors C1 - 2200µF 25VW electro C2 - 10µF 10VW electro C3 - 220µF 10VW electro C4,C7,C8,C10,C11,C12,C13, C14,C15,C16,C17,C18,C19, C31,C32 - 0.1 µF monolithic C5 - 27pF ceramic C6 - 0.22µF mono C9,C20,C21,C23,C24,C25,C26, C27,C28,C29,C30 - 1µF tantalum or LL electrolytic C22 - .0015µF greencap Resistors (0.25W, 5%) R1 -33Q, 2W R2-15Q, 1W R3-270Q R4-100Q, 2W R5,R33,R34,R26,R65 - 4.7kQ R6,R7,R9,R10,R14,R17,R18, R19,R20,R21,R22,R23,R25, R27,R31,R32,R38,R63 - 68kQ R8-3.9Q R11,R16-100kQ R12-180kQ R13,R29,R30,R43,R48,R53,R58, R62,R64 -1 0kQ R15 ,R24,R28 - 47kQ R35-1kQ R36-1 .5kn R37,R40 - 470kQ R39-220kQ R41 -820kQ R42,R46,R47,R51,R52,R56,R57, R61 - 150kQ R44,R45,R49,R50,R54,R55,R59, R60- 75kQ DISPLAY BOARD PCB1 - BURGDISP.PCB Beep1 - Sonitron SMA 14 Keypad1 - 12-way keypad J1 - 16-way IDC DIP L - link wire 300mm Screws - M3 x 12mm countersunk Pozidriv x 7 Nuts- M3 x 7 Washers - M3 shakeproof x 7 Standoffs - 6mm untapped x 7 Semiconductors LED1 ,LED3,LED4,LED5 - 5mm orange LED LED2 - 5mm red LED LED6 - 3mm green LED LED? - 3mm red LED IC1 ,IC2 - 74HC574 8-bit latch IC3 - 93C46 EEPROM DISP1 - HPDL 2416 4-character alphanumeric display Capacitors C1 ,C2,C3 -1µF 10VW electrolytic C4,C5,C6,C7 - 0.1 µF monolithic Resistors (0.25W, 5%) R1 ,R2,R3,R4,R5,R6,R7 - 1kn REMOTE KEYPAD Beep1 - Sonitron SMA 14 or equivalent beeper. PCB1 - BURGKEY.PCB Keypad1 - 12-way keypad TB1 - 4-way insulated screw terminal block SCKT1 - 28-pin IC socket BOX1 - plastic case (DSE Cat. H2857) Screws - M3 x 6mm countersunk Pozidriv x 4 Screws - M3 x 6mm pan head Pozidriv x 4 Washers - M3 shakeproof washers x4 Standoffs - 12mm untapped standoffs x 4 P1 ,P2,P3,P4,P5,P6,P7 - PC pins Heatshrink tubing - 70mm, thin RC - 7-way ribbon cable x 80mm Semiconductors 01 - 1N4004 D2,03-1N914 or 1N4148 IC1 - 68705P3 microcontroller Xtal1 -4MHz 01,02 - PN100 NPN transistor LED1 - 3mm green LED LED2,LED4,LED5,LED6 - 3mm yellow LED LED3,LED7 - 3mm red LED Capacitors C 1 - 220µF 16VW electrolytic C2 - 10µF 10VW electrolytic C3,C6 - 0.1 µF monolithic C4 - 27pF ceramic C5 - 1µF tantalum Resistors (0.25W, 5%) R1,R2-10kQ R3,R6- 4.7kQ R4,R5,R7,R8,R9 - 68kQ R10,R11,R12,R13,R14,R15, R16-1kQ attached to the common data bus. The 93C46 is capable of storing 32 16-bit words , which is more than enough for the alarm. When data is to be read or written to the 93C46, the CS line is taken high and this is done by addressing IC1 on the display board. When selected, data is fed serially to the EEPROM via lines PA3, PA4 and PA5 of the processor. As well as storing the time variables, the EEPROM is used to hold the current status of the alarm unit which will enable it to continue from where it left off in the event of a reset. As an example, let's suppose you activate the unit with sectors 1 and 2 on and the alarm panel subsequently loses mains power. This will cause a reset and the processor will download from the EEPROM, thereby placing th e alarm panel in the ON mode with sectors 1 and 2 active. Five 5mm LEDS are used to indicate the status of the unit (power, memory and sectors), while two 3mm LEDs (LEDs 6 & 7) flash alternately to indicate that the system is up and running. LED 1 (orange) on the front panel (top left) is on when the unit is activated while LED 2 (red) tells the user if the siren has sounded. LEDs 3, 4 & 5 (orange) are the sector LEDs and are alight if the sector is activated. The five 5mm LEDs are driven by latch IC2 which in turn is controlled by the MCU on the processor board. The MCU presents the new data to the inputs of IC2 and then takes the PC1 (clock) line low to latch in the new LED states. The two 3mm LEDs are driven from pin 17 ofIC1. Remote keypads At the heart of each remote keypad , is another 68705P3 microcontroller see Fig.4. This uses a different program to that of the main control unit but still runs on an interrupt of 20ms. The MCU takes care of the incoming and outgoing data streams, decodes the 12-way keypad, and controls the LEDs and beeper status. The software that controls communications between the alarm panel and up to two remote keypads has been written so as to allow uninterrupted operation of the processors at both ends. In other words, the keypad will still be decoded while a transmit or receive operation is in progress. The remote keypad circuit has been designed to store up to four pushed □1 1N4004 TB1 +12V n-----+-_t--_ __....., C2 10 + CJ .,. 1ovw.:r o.1J +5V OV~ +5V 7 3 6 TIMER VCC VPP 24 PA4t-.,._'VW~i,-t--.ir+---=-H PA3 23 ON -:-PB6 4 EXTAL +5V PB5 IC1 68705P3 C4 27pf+ PB4 P83 R9 68k 20 21 22 0 0 0) 0 0 © 0 G) © 0 © © P4 PB2 PAO KEYPAD1 P6 MEMORY 17 SECTOR 2 15 SECTOR 3 14 ENTER LED7 PA2 PB1 13 BEEP1 8 PCO g PC1 PC2 PC3 10 11 01! SECTOR 1 16 PA1 PBO P5 C6 18 RES GN □ 1 2 .,. .,. 12 28 C5 + ~K 1J P7 '"~'"' ' C0E VIEWED FROM BELOW GNO BURGLAR ALARM - REMOTE KEYPAD Fig.4: the remote keypad circuit is also based on a 68705P3 microcontroller (IC1). This unit decodes the 12-way keypad & takes care of the incoming & outgoing data streams on the Tx & Rx lines. It also controls the LED indicators. keys. Thus, if the 4-digit combination is quickly keyed in, each of the keys is placed in the transmit queue and waits to be transmitted. Under normal conditions, the processor constantly scans the keyboard and tests the Rx (receive) input to see if the start bit of an incoming message has appeared. The alarm panel MCU transmits an 8-bit word every 400ms. This 8-bit word contains such things as LED status, fault conditions and the beeper on/off soft switch. To commence the transmission, a start bit (logic 0) is sent which lasts for 20ms. The remote keypad detects this on its Rx input within 100µs of the line going low. The remote keypad MCU now adjusts its own internal driven interrupt so that it is 180° out of phase with the alarm panel's interrupt. This allows it to sample the next eight bits ofincom- ing data right in the middle of each bit, thus ensuring that each word is decoded properly. As soon as the eighth bit is received by the remote keypad, the two processors reverse roles (ie, the transmitting end becomes the receiving end and vice versa). If any key has been hit in the meantime, a 4-bit data stream is now sent from the remote keypad's MCU via its Tx circuit, back to the alarm panel where the data is decoded. The Tx circuits used in these keypads are capable of transmitting data over a distance of150 metres which should suffice for most applications. That's all we have space for this month. We'll continue next month with the construction and give full details on operating the unit. Complete kits plus accessories will be available from the author. SC SEPTEMBER 1992 63