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Build a keypad combination lock This keypad combination lock can be used to arm/disarm a house or car alarm, or to activate a solenoid-operated door strike. It accepts codes up to 12 digits long and is easy to program. Design by JEFF MONEGAL Keypad combination locks are a great idea in security applications, since they are far more convenient to use than keys. What’s more, the code can be quickly and easily changed at the user’s whim to restrict people who previously had access or just to maintain security. By contrast, keys can be easily copied or lost, while locks are expensive and time-consuming to change. The Keypad Combination Lock described here can be used in a range of security applications. These include: (1) turning bur­glar alarms on and off; (2) activating solenoid-operated locking mechanisms in security doors and 16  Silicon Chip gates; (3) controlling ignition killers and fuel cutout systems in cars and boats; and (4) oper­ating power doors on garages. When used with a home burglar alarm, the keypad would typi­cally be mounted just inside the front door. Alternatively, the keypad could be mounted in a weatherproof case just outside the door. That way, you could reduce the entry and exit delays to a bare minimum or simply wire the alarm for instant triggering. Main features Unlike previous circuits, this unit is based on a dedicated kepad com- bination lock IC and this has greatly simplified the circuitry. Called the UA3730, this 18-pin CMOS device contains all the necessary logic circuitry to monitor the keypad matrix, plus the necessary output logic for latched and momentary opera­tion. In addition, the chip includes onboard memory which is used to store the code. Up to 12 numbers can be stored in memory (for 1012 possible combinations) but this will depend on the level of security required. Unlike previous systems, the code can be quickly changed (provided you have access to the PC board), since there are no wire links to solder in or DIP switch­es to set. In most cases, a simple 4-digit code will give you adequate security while retaining the benefits of a number that’s easy to remember. This number of digits provides odds of greater than 10,000 to one against someone guessing the correct code. Of course, you can use more than four digits for even greater secur­ity (although it’s never D6 1N4004 IN +12V C3 1000 D1 IC2 78L05 GND OUT C4 10 D3 I G R6 1k A R8 14 10k B 8 7 5 R3 1k 16 IC1 UA3730 11 10 17 B E C K R4 1k B 1 2 3 C2 10 D5 1N4004 SIREN E Q2 BD140 C R4 1k B ALARM ON/OFF E 18 4 B O 13 S MEMORY SET LK1 K A Q3 BC548 15 6 P  LED2 C E PLASTIC SIDE C PIEZO BUZZER C5 0.1 9 3x1N4148 D2 KEYPAD 1 1 2 3 2 4 5 6 3 7 8 9 4 * 0 # 5 6 7 E R7 4.7k Q1 BD140 C R1 12k R5 1k A C1 270pF LOCK SOLENOID D4 1N4004  LED1 K VIEWED FROM BELOW KEYPAD COMBINATION LOCK Fig.1: the circuit is based on IC1 which is a UA3730 keypad combination lock IC. This device scans the keypad and, when the correct code is entered, the Alarm On/Off output toggles and the Lock Solenoid output goes high for two seconds. The piezo buzzer echoes the key presses. a good idea to use your telephone number). The keypad used is a standard 3 x 4 unit as used in some telephone diallers. It includes the digits 0-9 plus “✳” and “#” keys. Only the digits (0-9) can be used as part of the code but you can use the same digit more than once. Three outputs are provided by the Keypad Combination Lock: (1) Lock Solenoid (momentary); (2) Alarm On/ Off (latched); and (3) Siren. The unit is easy to operate – all you have to do is enter the correct code and press the “#” key. A small piezo transducer “beeps” briefly (for 0.2s) each time a key is pressed. Because it can only register one key at a time, you can’t fool the unit by simultaneously pressing all the keys at once. In addition, the IC includes a time-out feature so that you only have one minute to complete the code entry after the first key is pressed. If you take longer than one minute, the IC resets and you have to start all over again. When the correct code is entered, the Door Lock output goes high for two seconds (to open the door) and lights a red indica­tor LED. By contrast, the Alarm On/Off output alternately toggles between high (+12V) and open circuit (O/C); ie, it changes state each time the correct code is entered. The Alarm On/Off output can be used for switching burglar alarms or other equipment on and off, either directly or via a relay. Wrong code If the wrong code is entered, the transducer beeps once but only on the first two attempts. After the third incorrect at­tempt, the Siren output goes low for 60 seconds to sound an external siren or trigger a central alarm system. During this period, the transducer beeps once every second and the circuit lights an orange indicator LED. The circuit subsequently automatically resets at the end of the 1-minute alarm period. Alternatively, the circuit can be reset at any time during the alarm period by entering the correct code. Note that the use of any output is entirely optional. You might elect to Features Of The Keypad Combination Lock • • • • Based on a dedicated combination lock IC. • • • LED indicators for Lock Solenoid and Siren outputs. • Programmed code can be maintained in the event of power failure using three dry cells to provide battery backup. Accepts codes up to 12 digits long for 1012 possible combina­tions. Code is stored by the IC and is programmed from the keypad. Three outputs: (1) Lock Solenoid (momentary); (2) Alarm On/Off (latched); and Siren (1-minute alarm). Siren output activated if three incorrect codes entered in sequence. Piezo buzzer echoes key press­es; beeps once every second for duration of Siren output. September 1995  17 +12V GND SIREN DOOR LOCK D6 0.1 LED2 Q2 D5 1k 1k 10uF LK1 S P PIEZO BUZZER Q3 IC1 UA3730 12k 270pF 10uF 1k Q1 D4 1000uF IC2 4.7k 1k 1k 1 D1 D2 D3 10k ALARM ON/OFF LED1 2 3 7 4 5 16 TO CORRESPONDING NUMBERS ON KEYPAD 7 6 5 4 3 2 1 TO CORRESPONDING NUMBERS ON PCB BACK OF KEYPAD Fig.2: install the parts on the PC board as shown in this layout diagram. The two LEDs can either be mounted on the PC board, or they can be installed along with the keypad on the front panel of a case or switch plate. use only the Lock Solenoid output, for example, and leave the Alarm On/Off and Siren outputs disconnected. Supply requirements Because it is a CMOS device, the UA3730 has a typical quiescent current of just 5µA. This makes it suitable for battery backup using dry cells, since these will last for the length of their shelf-life. In fact, battery backup 18  Silicon Chip Take particular care when wiring the keypad, as some of the leads of the 7-way cable from the PC board have to be crossed over as shown here. Just be sure to connect the wiring exactly as shown in Fig.2. for the IC is desir­able since the memory is volatile. This means that the programmed code is lost if the power is interrupted, with the unit reverting to its default code of 0#. The circuit itself is powered from a 12V DC source, with the current requirements dictated by the external load. A typical door lock solenoid will require a supply capable of delivering about 400mA but many applications will require only 100mA or less. Battery backup is not a feature of the original circuit but it can be easily added, as we shall see later on. Note that the suggested circuit using dry cells is only suitable for main­taining the programmed code in the IC until regular power is re­stored. Circuit details Refer now to Fig.1 for the circuit details. Apart from the IC and the keypad, there are just two transistors, a 3-terminal regulator, a piezo transducer and a few minor parts. R1 and C1 are the timing components for IC1’s on-board oscillator. In operation, IC1 scans the keyboard matrix and decodes the key presses. The internal logic of the IC then de­ cides whether or not the correct code has been entered and wheth­er or not it has been entered in the required 1-minute period. Pins 17, 16 & 15 are the device outputs. Normally, pin 17 of IC1 is high and so PNP transistor Q1 is off. However, each time the correct code is entered, pin 17 goes low for two seconds and so Q1 briefly turns on and supplies current to the door lock solenoid. It also supplies current to LED 1 via a 1kΩ limiting resistor. At the same time, pin 16 changes state. If it was high before the code was entered, it switches low and Q2 turns on. Conversely, if it was low, it switches high and Q2 turns off; ie, pin 16 behaves as a latching output. The third output, pin 15, is normally high but switches low for one minute if three incorrect codes are entered in a row. This lights LED 2 and also drives an external siren circuit via diode D5 and current limiting resistor R4. At the end of the 1-minute period, IC1 resets and pin 15 switches high again. Pin 14 is the piezo driver output. Each time a key is pressed, this output generates a 3kHz signal for 0.2s which drives Q3. Q3 in turn drives the piezo transducer (B1) with this 3kHz pulse signal. R7 is necessary to provide a DC current path for the transistor. In addition, pin 14 generates a 0.2s burst at 3kHz each time an incorrect code is entered. It also generates a 3kHz burst every second for a period of one minute if three incorrect codes are entered (ie, while pin 15 is low). Pin 13 is used to control the pro- This view shows the programming jumper in the store (S) position. It must be placed in the program (P) position when a new code is to be programmed into the UA3730 IC. gramming function of IC1. Normally, this pin is left floating but is grounded (by install­ing link LK1) to program in a new code. The programming link is then removed again after the new code has been entered. This task has been made easy by installing a pair of adjacent 2-way pin headers on the PC board. A jumper is then used to short out two of the pins in one position to provide the programming link. The other position is simply used to store the jumper when programming has been completed. The Lock Solenoid output of the circuit can be used to drive a 12V door strike such as the unit shown here (available from locksmiths). Power for the circuit comes from an external 12V supply (battery or DC plugpack) and is applied to 3-terminal regulator IC2 via reverse polarity protection diode D6. The 5V regulated output from IC2 is then applied to pin 9 of IC1. Ca­pacitors C3, C4 & C5 decouple the input and output terminals of the regulator respectively. Note that transistors Q1 & Q2 are powered directly from the +12V rail. Construction All the parts except the buzzer and the keypad are mounted on a PC board measuring 105 x 60mm. This board carries a screen printed overlay so that you can see at a glance where each part fits. Fig.2 shows the assembly details. No particular order need be followed when installing the parts on the PC board but take care to ensure that all polarised parts are correctly oriented. In particular, note that the two BD140 transistors are installed with their metal faces towards the LEDs. There are four wire links on the board. Install these at the locations shown and install the two 2-way pin headers at the LK1 position. Separate pin headers are also installed for the buzzer terminals. Resistors R2 and R3 are shown as 2.2kΩ types on the PC board screened overlay but we recommend that you reduce them to 1kΩ, in line with the circuit diagram. Depending on the application, the two LEDs can either be installed directly on the PC board, as shown in Fig.2, or con­nected to the board via flying leads. Make sure that the LEDs are correctly oriented – the anode lead is usually (but not always) the longer of the two. It is a good idea to check PARTS LIST 1 PC board, 105 x 60mm, copyright Oatley Electronics 1 keypad 1 12V piezo transducer 1 plastic cable tie 1 200mm-length 7-way ribbon cable 1 18-pin IC socket 3 2-way pin headers 1 jumper (for pin headers) 1 80mm-length of tinned copper wire (for links) Semiconductors 1 UA3730 CMOS electronic lock (IC1) 1 78L05 3-terminal regulator (IC2) 2 BD140 PNP transistors (Q1,Q2) 1 BC548 NPN transistor (Q3) 1 5mm red LED (LED1) 1 5mm orange (LED2) 3 1N4148 signal diodes (D1-D3) 3 1N4004 silicon diodes (D4-D6) Capacitors 1 1000µF 16VW electrolytic 2 10µF 16VW electrolytic 1 0.1µF monolithic 1 270pF ceramic Resistors 1 12kΩ 1 10kΩ 1 4.7kΩ 5 1kΩ WHERE TO BUY A KIT A kit of parts comprising the PC board, all on-board parts, the keypad and the piezo transducer is available from Oatley Electronics for $20 plus $4 p&p. A suitable plastic case (see photo) costs an extra $4. Contact Oatley Electron­ ics, PO Box 89, Oatley, NSW 2223. Phone (02) 579 4985 or fax (02) 570 7910. Note: copyright the PC board associated with this design is retained by Oatley Electronics this point with your multimeter before the LEDs are installed. The red LED is used for LED 1 (alarm on/off), while the orange LED is used for LED 2 (ie, siren indication). The IC is best left until last. It is installed in an IC socket and must be oriented so that its pin 1 is adjacent to R1 (12kΩ). September 1995  19 Adding Battery Backup & Alarm On/Off Indication +12V R3 1k TO PIN16 IC1 E B Q2 BD140 C Programming 1k LED3 12V RELAY D9 1N4004  Fig.3: this diagram shows how to add LED indication and a relay to the Alarm On/Off output. If you don’t need the relay, just leave it (and D9) out. +12V D6 1N4004 IN C3 1000 IC2 78L05 GND 2x1N4004 D7 OUT C4 10 D8 C5 0.1 TO PIN9 IC1 4.5V Fig.4: here’s how to add battery backup to the circuit. Note that this circuit is only intended to maintain the code in the UA3730 IC in the event of a power failure. Once the board assembly is completed, it can be wired to the keypad via a 7-way ribbon cable. A cable length of 150mm should be sufficient for most applications. You will need to take extreme care when making the connections to the keypad, since some of the leads must be crossed over to reach their correct terminals. Just ignore the screened “1” on the PC board and connect the leads as shown in Fig.3. A plastic cable tie is used to anchor the keypad cable to the PC board, to stop the leads from coming adrift. Finally, the piezo transducer can be wired into circuit. Be sure to connect the red lead to the positive terminal. The Keypad Combi­nation Lock is now ready for testing. Testing All you have to do here is connect a 12V DC power supply to the unit and try it out. Wait a few seconds after switch on for the circuit to reset correctly – the piezo transducer will beep when all is ready. Now press 0# and check that LED 1 lights for two seconds and then goes out again. If it does, then all is 20  Silicon Chip If you strike problems, first check that the keypad is wired correctly, as it’s easy to make a mistake here. This done, check that all polarised parts are correctly oriented and that the correct part has been used at each location. well and you can check the other two outputs. To do this, use a multimeter (set to a low DC range) to monitor the Alarm On/Off output and check that this output tog­gles each time the correct code is entered. This done, check that the transducer beeps once every second and that LED 2 lights for a period of one minute when three incorrect codes are entered. Changing The Code The default code for the unit is “0” and this is entered by pressing “0” on the keypad and then pressing the “#” key. To change the code: (1) Place the jumper in the “P” (program) position of LK1. (2) Enter the desired code (up to 12 digits). (3) Press the “✳” key. (4) Transfer the jumper to the “S” (store) position of LK1 (this is necessary, otherwise the unit can be quickly reprogrammed from the keypad). To program the unit, first install the jumper between the two pin header terminals labelled “P” at the LK1 position (ie, between the two righthand terminals) – see Fig.2. Pin 13 of IC1 is now grounded. Now enter in the required code (up to 12 digits), press the “✳” key and transfer the jumper to the store (S) position. Your new code is now programmed into the lock. Check that the unit will recognise this code by keying it in and pressing the “#” key. Options (1) Alarm On/Off Indicator: Most burglar alarms sound a small buzzer during the exit and entry periods, so a LED indicator was considered unnecessary for the Alarm On/Off output. If you do need a LED indicator on this output, then it can be easily added as shown in Fig.3. Fig.3 also shows how this output could be used to drive a relay. Note that a diode must be connected across the relay coil to protect Q2 from voltage spikes when the relay turns off. (2) Battery Backup: A 4.5V battery pack (eg, three 1.5V dry cells) and a couple of 1N4004 diodes are all that are required to maintain the code programmed into IC1 if the power fails. Fig.4 shows how this is done. The circuit works like this: normally, the cathode of D7 is at 4.5V and so D8 will be reverse biased and no current flows from the batteries. However, if the power fails, D8 becomes for­ward biased and the backup batteries take over and supply IC1. D7 can be easily added to the existing PC board by substi­tuting it for the wire link immediately below the 1000µF capaci­tor (C3). Be sure to install it with its cathode lead to the right. D8 can be wired in series with the positive supply lead from the batteries and its cathode connected to D7’s cathode. (3) Door Sensor: Although not shown on the circuit of Fig.1, pin 12 is designated as the on/off sensor input. This pin is normally left floating but if YOU CAN AFFORD AN INTERNATIONAL SATELLITE TV SYSTEM SATELLITE ENTHUSIASTS STARTER KIT The two LED indicators can be affixed to the plastic case using epoxy resin, as shown here. Similarly, the keypad is attached by first drilling clearance holes for its four corner posts and then using epoxy resin to glue these corner posts to the inside of the case. it is shorted to the commoned anodes of D1-D3, the siren output goes low for one minute (ie, the effect is the same as if three incorrect codes are entered in sequence). Despite not being shown on the circuit, provision for this feature has been made on the PC board. All you have to do is wire the two unused pads to a normally open switch (eg, a reed switch or an under-carpet pressure mat), or even several switches wired in parallel. These switches could be used to detect other doors or windows being forced. YOUR OWN INTERNATIONAL SYSTEM FROM ONLY: FREE RECEPTION FROM Installation The exact method of installation will depend on the appli­cation but make sure that the electronic circuitry is secure so that the keypad cannot be circumvented. In most cases, the keypad can be mounted on a blank mains wall plate and this can be installed with the PC board behind it in a wall cavity. This means that the two indicator LEDs would also have to be mounted on the wall plate (eg, directly beneath the keypad) and connected to the PC board via flying leads. The LEDs can be secured using epoxy resin. Another option is to mount the keypad and circuitry in a plastic utility case and this method would be suitable for low-security applications. Power for the circuit can be derived either from a DC plug­ pack supply or from an existing alarm power supply, preferably with battery backup. Note that Mounting the circuit in a plastic case is OK if the alarm system has a battery for low-security applications. Alternatively, backup, then the optional batyou can mount the keypad on a blank mains tery backup circuit depicted in wall plate and hide the PC board close by in Fig.3 is unnecessary. SC the wall cavity. Asiasat II, Gorizont, Palapa, Panamsat, Intelsat HERE'S WHAT YOU GET: ● ● ● ● ● ● 400 channel dual input receiver preprogrammed for all viewable satellites 1.8m solid ground mount dish 20°K LNBF 25m coaxial cable easy set up instructions regular customer newsletters BEWARE OF IMITATORS Direct Importer: AV-COMM PTY. LTD. PO BOX 225, Balgowlah NSW 2093 Tel: (02) 9949 7417 / 9948 2667 Fax: (02) 9949 7095 VISIT OUR INTERNET SITE http://www.avcomm.com.au YES GARRY, please send me more information on international band satellite systems. Name: __________________________________ Address: ________________________________ ____________________P'code: __________ Phone: (_______) ________________________ ACN 002 174 478 September 1995  21