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A PC-Controlled Burglar Alarm System Fancy a full-featured alarm control panel with dialler capabilities? This one is PCprogrammed and controlled and can handle up to eight zones. The PC only needs to be powered up for arming and disarming, or you can use an optional keypad. Pt.1: By TRENT JACKSON 26  Silicon Chip B URGLAR ALARM SYSTEMS are hardly new but this DIY PC-controlled unit is something different. It’s an extremely versatile unit but despite that, it’s not expensive. In fact, the most expensive component used is the case but there’s nothing special about the unit specified. If you already have a suitable case, or can make one using materials to hand, you’ll save yourself about $30.00. A feature of this unit is that you siliconchip.com.au control two separate door strikes. Defined privileges can be used so that only certain individuals can arm and/or disarm certain zones. This effectively restricts access to certain parts of the building to certain people. As such, this system is ideally suited to the small business looking for a serious alarm system at a budget price. Of course, that’s not to say that it isn’t suitable for domestic use as well. It’s just that the wide range of access control that’s built into the system makes it very attractive to the commercial end of the market. PC options don’t need a keypad to arm and disarm it – that’s done using a PC. And if you’re wondering about a power blackout preventing you from powering up your PC to disarm the system, don’t be too concerned – a hard-wired “key” (which plugs into a D9 connector on the front panel) can be used to disarm the entire system if there’s a blackout or computer malfunction. Alternatively, for those that want a traditional keypad, a suitable unit will siliconchip.com.au be presented in Pt.2 next month. The keypad is entirely optional, however, and you still must use a PC to initially program the unit (ie, for setup). Eight zones Most low-cost alarms only cater for five or six zones but this unit can handle up to eight! Each of these zones can be independently armed or disarmed and monitored by the Windows-based software. In addition, the unit can You don’t need to have your PC permanently powered up and connected to the system in order for the alarm to function – at least, not unless you require the software-based dialler function. Of course, if the computer is left running, the monitor can be switched off (eg, overnight) and that’s good practice in most cases. As mentioned, the alarm is programmed via the software interface and all entry and exit delay times (from 1-255 seconds) are fully definable for each zone. The siren times are also definable and are also set from 1-255 seconds. This is well within the NSW legal limit of 300s (five minutes) but it’s a good idea to check the noise pollution regulations in your state before setting the siren duration. The system automatically rearms after the siren duration has expired and will immediately retrigger if further sensors are tripped. However, you can set the maximum number of trips for any one zone from 1-5, so that a faulty sensor will eventually be locked out. You can also set the maximum number of trips for all sectors combined, in this case to any number from 1-10 (more on this next month). As is common with all units of this type, the system has full battery backup (via a rechargeable SLA battery). If there is a blackout, this should be sufficient to keep the system operating for 1-2 hours, assuming a modest amount of peripheral components hanging off it – ie, PIRs and any other sensors requiring power. Access control The software access control is what sets this unit apart from conventional alarm control panels. It allows for up to four “Owners”, eight “Admins” and February 2006  27 Fig.1: the block diagram for the PC-Controlled Alarm. A PIC microcontroller arms and disarms the zones, scans the sensors and controls the alarm outputs and door-strikes. It also relays logging information back to the PC. 16 “Users”, each group having different privileges. Owners have the power to do whatever they like with the system, while Admins have the power to create and delete users and have almost full control over the system. Users have defined degrees of access only. The software is easy to use and you’ll pick it up in seconds – see “Driving The Software” in Pt.2 next month for further information. Another key feature is the logging side of things. Picture this: you run a small company with several employees working different shifts. Maybe you have a punch card or similar system or perhaps you rely on complete faith. In either case, this system allows for such monitoring. Employees enter the building at the start their shift and key in their PIN. The software places a date and time stamp next to their name within the log. You can then review 28  Silicon Chip this log on a regular basis to ensure that things are as they should be. But wait – couldn’t someone just enter their PIN and then go to the pub for a couple of hours? Well, that’s not possible due to the fact that you can set the system up to automatically rearm itself again, so that the PIN has to be re-entered at regular intervals The software-driven dialler feature works in a similar fashion to Leon William’s PIC-based dialler published in SILICON CHIP in April 2003. It uses your PC’s modem to dial a preset number and generate a tone across the line. Hard-wired key As previously mentioned, the “hard wired key” is used to disarm the system if a PC is unavailable (eg, during a blackout). It’s really very simple and consists of nothing more than a D9 connector and backshell, with just a few wire links used inside to set an inverted 4-bit code. Only 4-bit – hang on, isn’t that going to be easy to crack? Well no, because the key needs to be inserted (and removed) a preset number of times, as defined within the software. So, for example, you could wire the key for a code of 7 and specify that it has to be inserted and removed four times to turn the alarm off. If there is too much time taken between inserting and removing the key (or if it is done too quickly), the system fails to disarm. In practice, you need to leave about one second between each insertion and removal. Note that the hard-wired key can only be used to disarm the system and is intended for emergency use only. It cannot be used to arm the alarm. The D9 socket used on the front of the unit also has the RS232 connections for the PC on it as well (these RS232 connections are wired in parallel with a screw terminal block on the main PC board). This means that you could siliconchip.com.au also use a notebook computer to disarm the system in the event of a power failure or other malfunction. Alternatively, you may decide that it better suits your needs to actually use this socket for controlling the system at all times, rather than wiring the PC to the internal RS232 terminals. Two holes in the back of the unit allow for cable entry and exit, including the cables to the sensors, the external siren and the PC’s RS232 interface. The hard-wired serial cable is terminated in a D9 connector at the PC end. Sensors Almost any sensor with NO (normally open) or NC (normally closed) contacts can be used with the system. However, you must configure the setup for each sensor (NO or NC) in the Windows-based software. Basically, you can allocate NO or NC sensors for each zone but you can’t mix NO and NC sensors on the same zone. When activated (ie, when a sensor trips and the unit is armed), the alarm sets off a piezo siren located inside the case (and capable of producing around 119dB of sound). In addition, an external siren and/or strobe can be connected to the unit. An internal tamper switch will also immediately trigger the alarm if the lid of the case is removed while any of the zones are armed. In addition, there are two alarm outputs (Alarm OutA and Alarm OutB) which can be connected to The SILICON CHIP SMS Controller. These outputs are active high – ie, they switch high when any zone is triggered. LED indicators As shown in the photos, the unit is based on two PC board assemblies – ie, a main control board and a display board. The display board mounts on the front of the unit and carries 18 indicator LEDs. Eight of these LEDs are used to show which zones are armed, while another eight indicate the status of each zone – ie, whether it has been triggered or not. The remaining two LEDs function as power on/off and data transmit/ receive (Tx/Rx) indicators. The main control board carries a PIC16F877A microcontroller, along with a simple but effective power supply which delivers +5V and +12V rails. siliconchip.com.au Main Features HARDWARE FEATURES SOFTWARE FEATURES • • Eight independent zones. • Each zone can be configured to handle NO (normally open) or NC (normally closed) sensors. Windows-based interface – works with Windows 9x, Me, 2000 & XP. • Independent entry and exit delays for zones (1-255 seconds). • Battery backup plus tamper switch. • Programmable dialler feature (via a PC and modem). • Internal siren plus output for external siren. Automatic rearming features. • Two door strike and two alarm outputs. • • • Programmed and armed/disarmed via a PC. • • Hard-wired key to disarm unit if there is a power failure. Data logging with save, open and print facilities. • • Optional keypad to arm and disarm unit. Software shows how to configure hard-wired key to match code. • Software is easy to drive. This supply also provides a constant 13.6V 20mA (approx.) trickle current to charge the backup battery. The main board also carries the RS232 interface (which connects to the PC), along with screw terminal connector’s for all the off-board wiring to the sensors, external siren, door strikes and alarm outputs. In addition, there are a number of header sockets to handle the connections between the main board and the display board, and to provide the Alarm OutA and Alarm OutB outputs. Circuit details Fig.1 shows a block diagram of the unit. As previously mentioned, it’s based on a pre-programmed PIC16F877A microcontroller. In operation, the PIC micro accepts instructions from the Windows-based Ability to create three types of groups (owners, admins and users), each with different access privileges. software to arm and disarm zones and constantly scans for triggered sensors. It also drives the siren, LED indicator and alarm outputs, and there’s provision to control two door strike mechanisms. Finally, the PIC also relays information back to the PC for monitoring and logging purposes. Fig.3 shows the full circuit details (minus the power supply). Port lines RB0-RB7 of microcontroller IC1 monitor the sensor inputs via 2.2kW input protection resistors. These lines all have 100kW pull-up resistors to ensure they don’t float. Further protection is provided by inbuilt voltage clamps inside the PIC micro, so no damage will result if you do accidentally hook up 12V to these inputs. You may need to reset the system if this happens, though. Fig.2: this is the main GUI (graphical user interface) for the Windows-based software. The software is easy to drive and you can customise the setup to suit your particular application (full details next month). February 2006  29 30  Silicon Chip siliconchip.com.au Fig.3: the PIC microcontroller forms the heart of the circuit. It monitors all the inputs, arms and disarms the various zones and drives the status and alarm LEDs via IC3 & IC4. It also drives the siren and door-strike outputs via Darlington transistors Q1-Q4. Fig.4: the power supply uses a bridge rectifier (D1-D4) and 3-terminal regulators REG1 and REG2 to derive +12V and +5V supply rails. A 12V SLA battery provides the battery backup and this is charged via D6 and a 180W 5W resistor. This involves disconnecting both the plugpack and the battery, and then waiting for 30 seconds or so before reapplying power. Four BD681 Darlington transistors (Q1-Q4) control the door strikes and sirens via ports RD2 & RD3 and RC4 & RC5, respectively. These each have diodes connected between their collectors and the +12V rail, to protect the transistors from back-EMF spikes – eg, when a door strike turns off. A word of caution regarding the door strikes – the 12V rail is good for about 1A but only briefly! A door strike will draw around 700mA or so when activated, so don’t try to operate both door strikes at the same time. Microswitch S1 and its associated 100kW pull-up resistor on RD4 provide the anti-tamper feature. This line is normally held high when the lid is secured to the unit. However, if the lid is removed, this switch closes and pulls RD4 low. If any zone is armed, this automatically arms all other zones and sounds both the internal and external sirens. If this happens, all zones must then be disarmed and only “admins” and “owners” can do this (unless a “user” has full access). Clock signals for the PIC are provided by crystal X1 (4MHz). The two 22pF capacitors hanging off it ensure siliconchip.com.au correct loading for the crystal, so that it starts reliably. Two 4040 binary counters, IC3 & IC4, are used to drive the indicator LEDs on the display board. These counters are clocked by the RA0 and RA3 outputs, while RA1 and RA4 provide the reset signals (note: RA4 requires a 100kW pull-up resistor due to the fact that this pin can sink current but cannot source it). IC3 drives the Status LEDs (green), while IC4 drives the Armed LEDs (red). The two counter circuits work in exactly the same way, so we’ll just concentrate on the way in which IC3 operates. First, note that transistor Q5 is controlled via RA2 on the PIC. This is the enable line and Q5 turns on (via a 1.2kW resistor) when RA2 goes high. Initially, RA0 briefly swings high to reset the counter, after which (depending on the status of the zones) it is clocked by RA1. During this time, Q5 is off and so LEDs11-18 are also all off. Now let’s assume that Zones 1 & 4 have been triggered. Zone 1 has a bit value of “1” while zone 4 has a value of “8”. This means that in order for their corresponding LEDs to be lit, nine clock pulses must be applied to IC3’s clock input, so that outputs O0 and O3 go high. IC1’s RA2 output then goes high and turns on transistor Q5 to light LEDs11 & 14. This arrangement eliminates the need for multiplexing and reduces the amount of wiring required. The associated 330W resistors set the LED currents to a safe level. Alarm & RS232 outputs Ports RE0 & RD1 provide the two alarm outputs and these go high when ever an alarm condition occurs. These outputs can thus be used to trigger an external circuit that requires an active high (eg, the SMS Controller). RC0-RC3 are used for the hard-wired key socket. Normally, these inputs are tied high using 4 x 100kW pull-up resistors. Inserting the key in the D9 key socket then pulls one or more of A “hard-wired key” (actually a D9 connector wired with a 4-bit code) can be used to disarm the alarm if there is a power blackout. February 2006  31 Fig.5: install the parts on the main PC board as shown here but don’t plug in PIC microcontroller IC1 until after the test procedure described in Pt.2. Take care with component orientation. these inputs low, depending on the 4-bit code wired into the key. As mentioned above, this socket is also wired to the RS232 Tx and Rx lines (in parallel with an on-board screw terminal block). Data communication – either via the serial port or key socket – is achieved via ports RC6 & RC7. These communicate with the PC via a MAX232 serial data buffer (IC2). LED10 provides Tx/ Rx indication and is driven by port RE1 via a 330W resistor. In operation, LED10 normally flash­ es at varying speeds, regardless as to whether a PC is connected or not. In fact, there’s a very good chance that the circuit is working correctly if this LED is showing activity. Power supply Fig.4 shows the power supply circuit. It’s based on 3-terminal regulators REG1 and REG2 which provide the required +12V and +5V rails. Power is derived initially from a standard 16VAC plugpack rated at 1.25A. This is fed to bridge rectifier 32  Silicon Chip D1-D4, the output of which is then filtered using a 2200mF electrolytic capacitor and fed to REG1 via diode D5. In addition, the filtered supply rail from the bridge rectifier is fed via D6 and a 180W 5W resistor to a regulator circuit based on zener diode ZD1 and diode D7. This gives a nominal +13.6V rail to recharge the SLA battery at a current of about 20mA. The 12V rail from REG1 is used to power all of the peripheral devices that are connected to the alarm panel – eg, PIRs, sirens, strobes and door strikes. The output from REG1 is also fed to REG2 and its 5V output powers the PIC microcontroller and other logic circuitry. LED1 and its associated 2.2kW current-limiting resistor provide power indication. Diode D5 is there to ensure that this LED can only be powered from the mains-derived supply and not by the battery. This serves as a useful indicator that mains power is present. Diodes D8 & D9 ensure that the battery only supplies power to the circuit in the event of a mains power failure. Here’s how it works: normally, the cathode side of D8 sits at +12V due to the output from REG1. D9’s anode will at most have 13.2V applied to it under load and so no current flows through D8 & D9 while ever mains power is applied. However, when the mains power is disconnected, D8 & D9 become forward biased and the battery supplies a nominal +12V rail to power the peripherals and REG2. Building it Building this unit is dead simple. Fig.5 shows the parts layout on the main PC board (code 03102061), while Fig.6 shows the display board assembly (code 03102062). Before actually mounting any parts, check the two PC boards carefully for etching defects. It’s rare that you will find any problems but it doesn’t hurt to make sure. Also, be sure that the cutouts have been made in the corners of the main control board. These cutouts are necessary for the siliconchip.com.au Table 1: Capacitor Codes Value μF Code EIA Code IEC Code 100nF 0.1µF   104 100nF 22pF   NA    22   22p board to clear the plastic pillars inside the specified case. That done, you can begin the assembly by installing the parts on the main PC board. Install the wire links first, followed by the resistors and MKT capacitors – just check the code tables to decipher their values. It’s also a good idea to check the resistor values using a digital multimeter as they are installed. Once those parts are in, you can install the diodes, zener diode ZD1 and the electrolytic capacitors. These parts are all polarised, so take care with their orientation. Crystal X1 can go in next. It’s installed flat against the PC board with its leads bent at right angles so that they go through the relevant holes in the PC board. A U-shaped wire loop is then fitted over the crystal and is also soldered to its case. This not only secures the crystal in place but also connects its metal case to earth. IC sockets are used for the two ICs and these can be installed next. Be sure to install them the correct way around (ie, with the notched ends as indicated), to guide you when it comes to plugging in the ICs later on. IC2 can be plugged in at this stage but leave IC1 out for now – it’s installed later, after the power supply has been checked out. Be sure to install IC2 the right way around. Fig.6: the display board assembly. Note that connector CON4 is mounted on the track (copper) side of the PC board, while the LEDs have their leads soldered after the board has been mounted on the front panel – see text. Table 2: Resistor Colour Codes o o o o o o siliconchip.com.au No. 14 16 2 16 1 Value 100kW 2.2kW 1.2kW 330W 180W 4-Band Code (1%) brown black yellow brown red red red brown brown red red brown orange orange brown brown brown grey brown brown 5-Band Code (1%) brown black black orange brown red red black brown brown brown red black brown brown orange orange black black brown brown grey black black brown February 2006  33 Par t s Lis t 1 main PC board, code 03102061, 151 x 115mm 1 display PC board, code 03101062, 123 x 188mm 1 D9 female connector 1 D9 male connector 1 D9 backshell 3 16-pin DIL IC sockets 1 40-pin DIL IC socket 2 TO-220 mini heatsinks (6073B type) 1 100mm length of tinned copper wire (for links) 1 1m length 10-way rainbow cable 6 small cable ties (100mm) 2 large cable ties (300mm) 1 internal siren (optional), Jaycar Cat. LA-5255 or equivalent 1 16VAC 1.25A plugpack 1 12V 1.3Ah SLA battery 1 microswitch with extended actuator, Jaycar Cat. SM-1039 or equivalent 1 IP65 ABS case, 240 x 158 x 90mm (Jaycar Cat. HB-6134 or equivalent) 1 front panel label to suit 1 4MHz crystal (X1) 4 12mm tapped standoffs 16 M3 x 6mm screws 2 M3 x 20mm screws 16 M3 nuts 4 M3 shakeproof washers 2 PC stakes Connectors 1 10-way SIL locking pin header, 2.54mm, straight entry 2 10-way SIL locking pin headers, 2.54mm, right-angle entry 2 10-way header plugs, 2.54mm 1 4-way SIL locking pin header, 2.54mm, straight entry Now for the two 3-terminal regulators. These must first be secured to mini-U heatsinks using M3 x 6mm screws, nuts and shakeproof washers. Tighten the nuts firmly, then install the two regulators as shown in Fig.5 and the photo (don’t get them mixed up!), making sure that their heatsinks are well clear of diodes D10 & D11. Note that the two regulators face in opposite directions to each other. Next, install two PC stakes for the battery “+” and “-” connections. These are located just below the 180W 5W 34  Silicon Chip 1 4-way SIL locking pin header, 2.54mm, right-angle entry 2 4-way header plugs, 2.54mm 3 2-way SIL locking pin headers, 2.54mm, straight entry 3 2-way SIL locking pin headers, 2.54mm, right-angle entry 6 2-way header plugs (2.54mm) 13 PC-mount 3-way screw terminal blocks (5mm pitch) Semiconductors 1 PIC16F877A microcontroller programmed with PCCBA.hex (IC1) 1 MAX232 serial transceiver (IC2) 2 CD4040B binary counters (IC3, IC4) 4 BD681 NPN Darlington transistors (Q1-Q4) 2 BC548 NPN transistors (Q5,Q6) 15 1N4004 diodes (D1-D15) 1 13V 1W zener diode (ZD1) 10 5mm red LEDs (LED2-10) 8 5mm green LEDs (LED1 & LED11-18) 1 7812 12V regulator (REG1) 1 7805 5V regulator (REG2) Capacitors 1 2200mF 25V electrolytic 1 1000mF 16V electrolytic 5 100mF 16V electrolytic 4 10mF 16V electrolytic 6 100nF MKT metallised polyester 2 22pF ceramic Resistors (0.25W, 1%) 14 100kW 17 330W 16 2.2kW 1 180W 5W 2 1.2kW resistor, to the left of ZD1 and to the right of D7, respectively. The main board assembly can now be completed by installing the various screw terminal blocks and PC headers. Important: the screw terminal blocks must be mounted with their wire access sides facing inwards. If you mount them the other way around, you will not be able to connect the leads when the board goes in the case. Display board Now for the display board assem- Table 3: Wiring Connectors Connector Leads Length CON1 - CON1 10-way 31cm CON2 - CON2 2-way 35cm CON3 - CON3 2-way 38cm CON4 - CON4 4-way 28cm bly – see Fig.6. Once again, start with the links and resistors, then install the capacitors, transistors, IC sockets and PC headers. The two ICs can then be plugged into their sockets, taking care to ensure that they are oriented correctly. Note that the pin headers on this board are all right-angle types and that CON4 is mounted on the copper (track) side of the board (see photo). Next, fit 12mm standoffs to the four corner positions, securing them with M3 x 6mm screws. That done, the LEDs can all go in but don’t solder their leads just yet. Instead, install them as indicated in Fig.6 (take care with their orientation), then carefully secure the board to the lid of the case using another four M3 x 6mm screws. Make sure none of the LEDs fall out while you are doing this. Finally, the LEDs can be pushed into their matching front panel holes and their leads soldered. Of course, the above procedure assumes that you are building the unit from a kit and the case comes predrilled. If not, you will have to drill the front panel and make the cutout for the keyswitch yourself. The best way to do that it to use the front panel as a template to mark out the hole positions (it can be downloaded from the SILICON CHIP website – www. siliconchip.com.au). Similarly, you will have to drill four holes in the base of the case to take the cable ties that are used to secure the battery, along with mounting holes for the internal siren (if used). Additional holes also have to be drilled in the side of the case (to let the siren sound out), Finally, two large holes are drilled in the base (to the right of the battery) for the external wiring. Final assembly The accompanying photos show how it all goes together. The first step is to secure the battery in position using siliconchip.com.au This is the fully-assembled display board. Note that this prototype version differs slightly from the final version shown in Fig.6. two 300mm-long cable ties. Make sure these are nice and tight – you don’t want the battery to come adrift. That done, you can secure the siren using M3 x 6mm screws and nuts and then install the tamper switch. As shown in the photos, the tamper switch is mounted on the lefthand side of the case, above the PC board. It’s positioned about 7mm below the lip and is secured using two M3 x 20mm screws and nuts. Once it’s in position, bend its actuator arm upwards in an arc, so that the arm is held down when the lid is fitted (ie, to hold the switch open). The PC board is secured to the base using two screws that go into integral pillars at either corner on the bottom. Another two screws which overlap the top edge of the board go into integral pillars in the centre of the case. The construction can now be completed by installing the wiring. This mainly involves fitting plug headers to lengths of multi-way (rainbow) cable to connect the two boards together – ie, for headers CON1-CON4. Table 3 shows the details for these cables. siliconchip.com.au Be sure to connect the leads to the plug headers correctly. It’s just a matter of connecting each lead to its matching pin on each header (ie, pin 1 to pin 1, pin 2 to pin 2, etc. In addition, you have to install the wiring between the D9 female socket and the keyswitch header, after which you can secure the socket to the front panel. You also have to install the wiring to the tamper switch, the internal siren and the battery. Note that there are three terminals on the tamper switch: COM, NO and NC. You have to connect the two leads from the terminal block to the COM and NC terminals, so that the switch goes open circuit when the actuator arm is held down by the lid. Use a red lead for the battery positive connection and a black lead for the negative connection. These two leads are soldered at one end to the PC stakes on the main PC board and are fitted with spade clips at the other end to match the battery terminals. It’s a good idea to cover the connections to the PC stakes with heatshrink tubing. This not only insulates them The microswitch is mounted about 7mm below the lip of the case. Bend its actuating arm upwards as shown, so that the switch is held open when the lid is in place. but also stops the wires from flexing and breaking at the solder connections. Finally, use cable ties to bind the wiring together, as shown in the lead photo. This not only keeps it tidy but also ensures that it folds back neatly into the case when the lid is closed. Next month That’s all we have space for this month. In Pt.2, we’ll give the test procedure, detail the software and describe the hard-wired key­switch and SC the optional keypad unit. February 2006  35