|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Combination lock with numeric keypad. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Safety and security The proposed electronic combination lock is very simple, assembled from a small number of parts. It is highly reliable in operation, equipped with a numeric keypad for entering a code of eight digits, an alarm activation unit when a wrong code is entered, and is protected from errors when pressing several buttons at the same time. The device can be constantly turned on, as it is made on CMOS chips and consumes negligible current from the power source. Many different designs of electronic combination locks were described on the pages of the Radio magazine, for example, [1, 2]. However, interest in such devices is still great. Locks differ in complexity, secrecy, and the way the code is entered. Many of them are with one- or two-button control. Still, devices with a numeric keypad remain the most popular. They allow you to achieve great secrecy while maintaining ease of use. A diagram of such a combination lock is shown in fig. 1. On the counter-decoder DD2 and the controlled clock generator on the elements DD1.1 and DD1.2, a protection unit against simultaneous pressing of several buttons is made. The DD3.1 counter counts the number of entered digits, and the DD3.2 counter counts only those that match the code. The single vibrator on the elements DD1.3 and DD5.1 suppresses contact bounce when the buttons are pressed. On the DD4 multiplexer, a node for comparing the entered digit with the code is assembled. Element DD5.3 turns on the alarm device if the wrong code is entered. The R4C3VD1 circuit provides the initial installation of the device (resetting the counters of the DD3 chip).
In the initial state, the outputs of the counters DD3.1 and DD3.2 have a low voltage, the clock generator on the elements DD1.1 and DD1.2 generates pulses that arrive at the counting input of the counter-decoder DD2, at the outputs of which a single signal appears in series. At the address inputs of the multiplexer DD4 - low voltage, which corresponds to the connection of its output to the input D0. When a button is pressed, for example "3", at the moment a single signal appears at the corresponding output of the counter-decoder, a single vibrator is started on the elements DD1.3 and DD5.1. At the output of DD5.1 - a low-level voltage that prohibits the operation of the clock generator. If the number "3" is correct, a single signal present at the input of the multiplexer is transmitted to its output, allowing the increment of the value of the counter DD3.2 by one. The change in the state of the counter will occur on the decline of the pulse at the output of the single vibrator. Counter DD3.1 will also increase its value by one. If the dialed digit is incorrect, only the state of the counter DD3.1 will change. As long as a single signal is present at the output of the one-shot, pressing other buttons or chattering the contacts of the one already pressed will not cause a change in the state of the device. Entering the next digit will connect the D1 input of the multiplexer, etc. If the code is entered correctly, after dialing the eighth digit, a single signal appears at the output 8 of the counter DD3.2, allowing the operation of the lock actuator; at the output of the element DD5.3 there is a zero signal that prohibits the operation of the signaling device. When dialing the wrong code, the number in the counter DD3.2 will be less than in the counter DD3.1. This will cause a high level voltage to appear at the output of the DD5.3 element and turn on the alarm. When you press any button, the capacitor C3 is discharged through the diode VD1 and the output circuits of the element DD5.2. After that, for some time (with the specified values of the resistor R4 and capacitor C3 - about 4 s), the voltage across the capacitor C3 reaches the threshold level for resetting counters DD3.1 and DD3.2. This is necessary so that in case of an error in entering the code, you can repeat the dialing after a while. The time delay creates additional difficulties for the attacker, since it takes a lot of time to try to guess the code. Pressing the button should be short, less than the duration of the pulse generated by the single vibrator on the elements DD1.3, DD5.1. Otherwise, if the key remains pressed, the one-shot will start again and the same number will be entered again. For an attacker, this will also become an additional barrier. Installing the code comes down to soldering the jumpers between the outputs of the counter-decoder and the inputs of the multiplexer (code 14236757 is indicated on the diagram). The number of possible combinations is 10 8 , which is higher compared to, for example, [1]. If necessary, the number of digits in the code can be reduced to four by connecting the lower (according to the diagram) input of the DD5.3 element to output 4 of the DD3.2 counter, and the upper input to output 4 of the DD3.1 counter, previously disconnected from the circuits used earlier. Unused inputs of the DD4 chip should be connected to a common wire. Naturally, the secrecy of the castle in this case will be lower. The alarm device must be switched on by a high-level voltage and work after bringing the electronic part of the lock to its original state. Resetting the device to its original state can be performed with a separate button placed along with the others. To do this, it is necessary to exclude the elements R4, C3 and VD1 by connecting a 100 kΩ resistor between the connection point of pins 7 and 15 of the DD3 chip and the common wire and an additional button between this point and the power wire. The reliability of the device will increase slightly if any silicon diodes (for example, KD5.2A) are connected as anodes to the buttons between each button and the connection point of the resistor R521 with the lower (according to the diagram) input of the DDXNUMX element. It is desirable that the signaling device, when turned on, blocks the further operation of the lock, for example, turns off the power to the electronic part. If this is not provided, you can modify the lock according to fig. 2, having previously disconnected output 5 DD1.2 from the rest of the circuits. After turning on the signaling device, the operation of the clock generator will be blocked, which will complicate further attempts at code selection.
The electronic part of the code lock is made on a printed circuit board made of one-sided foil fiberglass. The keypad must be in close proximity to the printed circuit board to avoid noise induced in the long connection cable. Its design can be arbitrary. For example, it is acceptable to use a keypad from a keypad phone (in this case, you need to change the connection of its keys). The device is powered from a stabilized power supply with a voltage of 9 ... 15 V. Since the device consumes a rather small current in idle mode, it is possible to introduce a backup power source in case of a power outage. Device chips can be replaced with similar 564 or K176 series. In place of VD1, any silicon pulse diodes are applicable, for example, D220, KD503A. Resistors and capacitors can be of any type, suitable in size. In the immediate vicinity of the microcircuits, ceramic blocking capacitors with a total capacity of 0,047 ... 0,5 μF (not shown in the diagram) must be connected to their power circuits. The described code lock, assembled without errors, starts working immediately. It is only required, if necessary, to set the necessary time delays: by selecting resistor R2 - to eliminate contact bounce after pressing the button and resistor R4 - to bring the device to its original state. In the author's version, the electronic part of the code lock is mounted in a case from a SPECTR-305 push-button telephone set. Power is supplied from a source with a quenching capacitor. The mechanical part is an electromagnet from the RKM-1 relay (passport RS4.500.841), which unlocks the lock (similar to that described in [1]). For a more accurate operation of the device, it is recommended to connect a resistor with a resistance of 2 ... 5 kOhm in series with the capacitor C10. Literature
Author: S.Kuleshov, Kurgan
Machine for thinning flowers in gardens
02.05.2024 Advanced Infrared Microscope
02.05.2024 Air trap for insects
01.05.2024
▪ Stratasys Objet Eden3V 260D printer for dentists ▪ B&K PRECISION 1541D Dual Channel Oscilloscope ▪ Transcend CFexpress 820 Type B Memory Cards ▪ The thermal imager will expose the scammer ▪ CC3200+CC2650 Wireless Gateway Connects BLE Sensors to the Internet
▪ section of the site Videotechnique. Article selection ▪ article graphite. Tips for the home master ▪ article What rule did Peter I establish for speakers in the Senate? Detailed answer ▪ article Electrician of lighting and power networks. Standard instruction on labor protection
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page