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Burglar alarm keypad & combination lock This keypad combination lock can be used to arm/ disarm your house or car alarm, or to activate a solenoid-operated door strike. It will also trigger the alarm when it detects seven consecutive incorrect entries, to defeat unauthorised tampering. By GREG SWAIN Although burglar alarms are a good idea, they can also be very inconvenient to operate. In particular, you always have to be sur8 to leave or re-enter the house during the fixed exit and entry delay periods to avoid falsely triggering the alarm. Another drawback is having to fumble around for the alarm key each time you want to switch the alarm on or off (ever accidentally set off your alarm and 28 SILICON CHIP couldn't find the key?]. Now you can have all the advantages of a home burglar alarm without the disadvantages . This easy-to-build Burglar Alarm Keypad is designed to mount near your front door and lets you turn the alarm on or off by pressing a few buttons. With this device, there's no need to make a mad dash for the front door as soon as the alarm is armed. Although designed for the MultiSector Burglar Alarm described in the June 1990 issue of SILICON CHIP, the Burglar Alarm Keypad will suit just about any house alarm circuit. It uses easy-to-get parts and is a snack to build and get going. Typically, the keypad would be mounted just inside your front door but it could also be mounted in a weatherproof case just outside the door. In the latter case, you could get rid of the exit and entry delay periods altogether and just wire the alarm for instant triggering. Other possible applications of the device include switching mains power to a computer or some other appliance to prevent unauthorised use, switching a telephone line, arming/disarming an ignition killer circuit in a car and controlling power doors on garages. 22k ------------....------- ------0+12VDC INPUT 14 01 7 4 CK 03 04 10 2 g CK IC2d 4093 IC1 4017 01 12 01 CE 3 00 RST CE 15 8 13 02 BC548 ':' .,. .,. +V MONO B ALARM TRIGGER IC3a 04 EO c +v 16 1D CE 02 03 WIRE LINK PRE SET S (758 #) 011 16 ,, LATCH 330k +V VIEWED FROM BELOW BURGLAR ALARM KEYPAD Fig.t: initially, decade counter ICt is reset & QO is high. If the correct code keys (758#) are pressed, the counter is clocked and the Qt, Q2, Q3 & Q4 outputs switch high in sequence. The high on Q4 then turns on transistor Qt for monostable operation or toggles counter IC3b for latched operation. IC3a counts the number of incorrect entries. Operation To activate the lock, you just press four keys on the keypad in the correct sequence. When this happens, the circuit switches a relay whose contacts are wired across the ARM/DISARM switch of the burglar alarm. However, if you strike an incorrect key during the code entry, the circuit automatically resets and you have to start again. A LED indicator at the bottom of the keypad lights whenever the circuit is armed (ie, when the relay contacts close). This LED could also be mounted at some remote location or it could be left out altogether if you don't want it. You select your own 4-digit code when building the unit, by installing wire links on the PC board. You also have the option of wiring the circuit to provide latched or monostable relay operation. This involves installing a single resistor in one of two positions. In the latched mode, the relay changes state each time the correct 4-digit code is entered. If you want to turn a burglar alarm on and off, this is the mode to use. Alternatively, in the monostable mode, the relay contacts close for only a short period to activate a door strike or whatever. put open circuit to set off the alarm. y OU can ignore the ALARM TRIGGER output if you don't wish to make use of this feature . It can be regarded as a useful optional extra in security applications. Coding How it works As can be seen from the photographs, there are 12 keys on the keypad: the digits 0-9, plus * and # keys. Any four of these keys can be used for coding while pressing any of the remaining keys will clear (or reset) the circuit. In practice, you would normally decide to use one key only to reset the circuit if you run into any problems during code entry. For example, you might decide to always use * as the reset key and choose the code 09#5. Alternatively, you could choose an all digit code (eg, 7581). Because they can be included as part of the code, the * and # keys dramatically increase the odds against someone guessing the correct code. And what are those odds? Well, assuming the person knows that he must enter a 4-digit code, the odds are greater than one in 20,000. Even if he knows that the same number cannot be used consecutively (which it can't), the odds are still approximately one in 16,000. What's more, if the circuit detects seven incorrect key entries, it switches its ALARM TRIGGER out- The circuit is simple yet ingenious - see Fig,1. There are just three low-cost CMOS ICs, two transistors, a relay, a small keypad and a few other minor components . Let's see how it works. IC1 is a 4017 decade counter with 10 decoded outputs. Its Q0-Q3 outputs are connected to lines 1, 2, 3 & 4 via isolating diodes D1-D4. Each of these lines in turn connects to one side of a single key while the remaining keys all go to the Clear [C) line. The other sides of the keys are commoned and connected to the clock (CK) input of IC1. Fig.1 shows the circuit configuration for a code of 758#. That's because line 1 is connected to key 7, line 2 to key 5, line 3 to key 8 and line 4 to#. The code can be changed simply by connecting different keys to each of these lines. Initially, IC1 is reset which means that Q0 is high and its other outputs are all low. Now let's assume that the correct code is entered. When key 7 is pressed, a positive going clock pulse is applied to pin 14 of ICl via D4 and the closed key contacts. This clocks the ]UL Y 1990 29 PARTS LIST FROM ALARM KEYPAD _.....:----0----<>-----<>--->---0 1 TO SECTOR INPUT 1 1 HO AHO NC SWITCHES Fig.2: here's how the ALARM TRIGGER output is connected to the alarm sensor wiring loop. Note that some circuits will require a different value of load resistor. In that case, just substitute the required value for the 10kQ resistor shown. 1 4 4 4 4 PC board , code ZA-1450, 105 x 50mm (copyright DSE) PC board, code ZA-1451 , 85 x 50mm (copyright DSE} keypad , DSE Cat. K-8403 12V SPOT relay, DSE Cat. S-7120 6-way PC terminal block 6mm spacers 6BA x 1 2mm machine screws 6BA nuts 3mm nuts (for use as keypad spacers) Semiconductors counter which clears QO (ie, switches it low) and sets Ql high. Pressing key 5 now applies a further clock pulse to pin 14, this time from Ql via D3. This clears Ql and sets QZ high. Similarly, Q3 switches high when key 8 is pressed, while Q4 switches high (and Q3 clears) when # is pressed. Thus, Q4 switches high each time the correct 4-digit code is entered. However, if an incorrect key is pressed at any time (ie, any key connected to the clear line), pin 1 of Schmitt NAND gate ICZa will be pulled low by the 22krl resistor on pin 14 of ICl. This switches pin 3 of ICZa high and resets ICl, which means that you have to start all over again. When Q4 of ICl switches high (when the correct code is entered), Below: the parts are all assembled on two PC boards which are connected by short wire links. The keypad board is then folded over & mounted on the back of the main circuit board. it clocks IC3b which is one half of a dual BCD counter. This sets QO (pin 11) of IC3b high. If the circuit is wired for latched operation, this high turns on transistor Ql which then switches on the relay and the LED indicator (LED 1). The high on Q4 also charges the O. lµF capacitor on pins 5 & 6 of ICZb via a 330krl resistor. After a brief delay (33ms with the values shown), pin 4 of ICZb switches low and resets ICl via ICZa (ie, QO high and all other outputs low). The O. lµF capacitor (Cl) then discharges via the 330krl resistor (Rl) into Q4 to remove the reset signal from ICl after about 33ms. This resetting procedure has no effect on IC3b as it responds only to positive-going clock signals. Its QO output can only be cleared by entering in the correct code again. When that happens, Q4 of ICl switches high again and IC3b switches its QO output low. Thus, QO of IC3b changes state each time the correct code is 1 4017 decade counter (IC1) 1 4093 quad Schmitt NANO gate (IC2) 4518 dual BCD counter (IC3) 2 BC548 NPN transistors (01,02) 4 1 N4148 diodes (D1 -D4) 1 1 N4002 diode (D5) 1 5mm red LED (LED 1) Capacitors 2 0. 1 µF monolithic 1 1 µF (C 1 , monostable operation only) Resistors (0.25W , 5%) 1 1 Mrl (R 1 , monostable operation only) 2 330krl 1 1 Okfl 3 22k0 1 1.5krl entered, to switch the relay either on or off. For monostable operation, output Q4 of ICl drives transistor Ql directly via its zzkn base current limiting resistor. As we 've already seen, Q4 goes high each time the For Features and Perl ormance ... YOUR COMPLETE ALARM SUPPLIER DOMESTIC RADIO REMOTE CONTROL SYSTEM. This unique system comes in 2 models - a single channel and a dual channel. the single channel can be used to trigger the alarm's 24 hour/panic sector. 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A [] □ EJ [:] □ □ [] [:] 7 • .. • [:][:JC:JG Fig.3: for latched operation, connect the 22kn resistor adjacent to Qt to point L; for monostable operation, connect the resistor to point M and change Rt & Cl. The diagram shows how the wire link presets are installed for a code of 095# but you should devise your own code. correct code is entered. This switches transistor Ql on to close the relay contacts for the period set by the RlCl time constant (note: these values are increased for monostable operation}. Incorrect entries IC3a counts the number of consecutive incorrect entries when the circuit is armed (ie, when QO of IC3b is high}. Each time an incorrect number is pressed, pin 1 of IC2a is pulled low and pin 3 switches high to generate a reset pulse for ICl. This reset pulse also clocks IC3a (pin 1}. After eight reset pulses (one pulse from entering the correct _,_,.,.,, ...__ _ 'C · .. ) \ combination plus seven pulses from incorrect entries}, Q3 of IC3a switches high and IC2c turns off transistor Q2. It also pulls the clock enable (pin 2) low to disable the counter, so that the Q3 output (pin 6} stays high. Transistor QZ functions in the same way as a set of normally closed sensor contacts. When it turns off on the seventh incorrect entry, it immediately triggers the external alarm circuit. Fig.2 shows how the ALARM TRIGGER output is wired to form part of the resistive wiring loop to the alarm sector input. The circuit is simply substituted for the 10k0 load resistor that's normally included in the loop to the MultiSector Burglar Alarm. (Note: some alarm circuits may require a different value load resistor. In this case, the required value should be substituted for the 10k0 resistor shown}. IC3a is reset when the correct code is entered to disarm the circuit (and switch off the alarm}. As soon as the correct code is entered, QO of IC3b goes low and IC2d pulls IC3a's reset terminal (pin 7) high. This switches Q3 of IC3a low and turns on transistor Q2 via IC2c to simulate closed sensor contacts. IC3a is held in the reset state for as long as the circuit is disarmed. Construction All the parts are mounted on two small PC boards coded ZA-1450 and ZA-1451. The ZA-1450 board holds all the active circuitry while the ZA-1451 board holds only the keypad and the LED indicator. Fig.3 shows the assembly details for the two boards. The parts can be mounted in any order but we suggest that you leave the relay and output terminal block until last. Make sure that the ICs, transistors and diodes are all installed with the correct polarity. Pin 1 of each IC is adjacent to a notch in one end of the plastic body. Note particularly that D3 faces in the opposite direction to D1, D4 & D2. Note also that D5 is a 1N4002 type. Where to buy the kit The completed assembly can be installed in a weatherproof case or mounted on a electrical switch plate. The LED indicator beneath the kepad lights when the circuit is armed. 32 SILICON CHIP This project was developed by Dick Smith Electronics and is available from all DSE stores or by mail order from PO Box 321 , North Ryde , NSW 2113 . You can also order by phone on (02) 888 2 105 or, if you are outside the Sydney area, on (008) 22 6610 . The kit consists of two etched PC boards plus all the necessary components (including the keypad). Alternative-values for R1 & C1 are supplied so that the kit can be built for either latched operation or monostable operation (one second relay pull-in time). The price is as follows: Burglar Alarm Keypad (Cat. K-8 403) ..... .. .. .... ... .. .. .. .. ..... ... .. . $29.95 Postal orders should add another $4.50 for p&p. Please quote the catalog number when ordering. Note: copyright of the PCB artworks associated with this project are retained by Dick Smith Electronics. This circuit hoard has been assembled to give latched operation from an entry code of 095#. Note that the coding lines are not in sequence but run C3421 (see Fig.3). There are two options when it comes to installing the 2 2kQ resistor adjacent to Ql. Connect this resistor to point L for latched relay operation or to point M for monostable operation. The values shown on Fig.3 for Rl & Cl are suitable for latched operation but this time constant will have to be increased for monostable operation. It's simply a matter of choosing a suitable time constant to give the required relay turn-on period. For example, if Rl = lMQ and Cl = lµF, the time constant (and hence the relay turn-on time) would be 1 second. Other possible values are 2.2MQ & 33µF (72 seconds); lMQ & 22µF (22 seconds); and 330kQ & 22µF (7 seconds). The keypad is mounted on its board using four 3mm nuts (one on each mounting post) as spacers. Check that all the pinouts from the keypad protrude through the holes in the board, then secure the keypad by using your soldering iron to "burr over" the plastic mounting posts. The keypad terminals can then all be soldered and the LED installed. Watch the polarity of the LED the flat side of the plastic body is adjacent to the cathode (K) lead. Install the LED so that its top is level with the tops of the keys. Coding links The coding links (wire link presets) are best installed before the two PC boards are hooked to- The keypad hoard is mounted on the back of the main circuit board on 6mm spacers and secured with machine screws & nuts. Four 3mm nuts are also used as spacers when mounting the keypad on its board. gether. These are installed down the lefthand side of the ZA-1450 board. You can use any 4-key code you like (including * and #) and you can use the same key twice but not consecutively. For example, you can program in the code 1525 but not 1552. To program in the code, connect the four selected key outputs to the 1, 2, 3 & 4 lines. The outputs of the remaining eight keys are then all connected to the C (clear) line. Fig.3 shows how the circuit is connected for a code of 095#. That's because key O is connected to line 1, key 9 to line 2, key 5 to line 3, and key # to line 4. Note that the coding lines run 1, 2, 4, 3, C (from left to right). The two boards can now be connected together using 15 25mm-long insulated wire links. Finally, fold the keypad board over and mount it on the back of the circuit board using 6mm spacers and 6BA machine screws and nuts. Testing To test the unit, connect up a 12V power supply and press a clear key (any key that's not part of the code). Now enter in the correct code and check that the relay operates and that the LED comes on. The relay should latch on if you have installed the 22kO resistor in the latch (L) position or pull in for the preset time if you have chosen the monostable (M) position. Now check that the relay turns off again when you re-enter the code (latched mode only). This done, rearm the circuit (ie, LED indicator on) and use your multimeter to monitor pin 10 of IC2c while you press a clear key seven times. Pin 10 should start off high but should switch low on the seventh press of the key. Depending on your application, the completed unit can be mounted in a plastic zippy box or you might like to consider mounting it on a standard electrical switch plate. In either case, you would have to make a neat cutout to suit the keypad and drill a hole to accept the LED. The switch plate idea is the one to go for if you intend mounting the unit inside your house. ~ JULY 1990 33