Electronic combination lock with key. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Electronic combination lock with key. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Safety and security

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A lot of electronic combination locks are described in amateur radio literature. But most of them have a push-button dialer, and sooner or later the code becomes known to outsiders for one reason or another. As a result, it has to be changed periodically. In the proposed article, a lock is considered, the key to which is a metal plate with holes.

The key is a metal plate (Fig. 1) with eight holes drilled into it. They are located in two rows and correspond to the binary code installed in the lock. If the code bit is "1", then the hole will be in the top row, and if "0" - in the bottom. Like a mechanical key, the key is inserted into the reader's hole. A binary code is read from the key, similarly to a punched card, compared with the given one, and if it matches, a relay is turned on, through the contacts of which power is supplied to the lock electromagnet.

Electronic combination lock with key

The appearance of the reader is shown in fig. 2.

Electronic combination lock with key

It is made in the form of a hole for a key and consists of several parts (Fig. 3): plates for photodiodes 2; plates for emitting IR diodes 5; gasket 4, the thickness of which should be slightly greater than the thickness of the key so that the key can fit tightly into the well; diaphragm 3 and fixing bolts 1.

Electronic combination lock with key

The scheme of the device is shown in fig. one.

(click to enlarge)

In the through holes of plates 2 and 5, optocouplers of IR diodes VN, BI2 and photodiodes BL1, BL2, respectively, are fixed perpendicular to the holes in the key. They serve to read information. The optocoupler from BI3 and BL3 fixes the final position of the key.

When the key is inserted into the keyhole, it blocks the optocouplers VI-BL1 and BI2-BL2. As the key moves, when a hole passes through the optical axis of the optocoupler, the radiation from the IR diode through the hole in the key enters the photodiode. Depending on the state of the bit ("0" or "1"), one of the photodiodes lights up. BL1 corresponds to one, and BL2 to zero. If BL1 is illuminated, then a high level appears at the output of the element DD1.1, which is fed to the input D of the shift register DD3.1 and through DD2.1 and DD2.2 to the clock inputs C of the registers DD3.1 and DD3.2. The received bit "1" is written to register DD3, and the code is shifted.

A similar process occurs when writing bit "0" to the register. When BL2 is illuminated, a high level appears at the output of DD1.2. At the output of DD1.1 at this moment there is a low level, which is written to the register DD3.

The code written in the registers DD3.1, DD3.2 is compared by the XOR elements (DD4, DD5) with the code typed using jumpers on the X1 connector. If the code completely matches, all outputs of the DD4 and DD5 microcircuit elements will be set to a low level. At the same time, the inputs 13 and 12 of the DD2.3 element are also low.

After all eight holes pass the read optocouplers, the front end of the key will reach the BI3-BL3 optocoupler and block it. A low level will appear at the output of the DD1.3 element, which will go to the input of DD2.3 (pin 11). A high level will appear at the output of the DD2.3 element, which will open the transistor VT1. Relay K1 will turn on and its contacts will apply voltage to the winding of the electromagnet Y1.

The device can use chips of the K176, K561, K564 series. Relay K1 - RKC3 (passport RS4.501.200) with a winding resistance of 175 ohms. Another type of relay can be used, the contacts of which are designed for the operating current of the electromagnet Y1. Electromagnet Y1 must be rated for alternating current if it is supposed to be powered directly from a 220 V network. Transformer T1 can be used ready-made. The secondary winding must provide a voltage of 36 V at a current of 0,3 A and have a tap from the middle of the winding.

Detail drawings for the reader are shown in fig. 5 - 8 (details 2 - 5 respectively).

Electronic combination lock with key

Plates 2 and 5 are made of textolite 15 mm thick, gasket 4 is made of duralumin or steel 2,5 mm thick, diaphragm 3 is made of tin 0,5 mm thick. The dimensions indicated on the drawings should be followed only if you use the program to make the key. Otherwise, the dimensions of the parts may be different.

After assembly with bolts 1 (see Fig. 3), parts 2, 3, 4, 5 are clamped so that they move relative to each other with little friction. Then, looking at the clearance through the holes for photodiodes, the key is inserted and by moving the parts, the axes of the holes in the key, aperture 3 and the axes of the photodiodes and IR diodes in plates 2 and 5 are aligned. After that, the parts are finally clamped. Photodiodes are installed in plate 2, and IR diodes are installed in plate 5 at a distance of approximately 7 mm from the diaphragm.

A simple program shown in the table will help you make a key template. It is written in QBasic.

Electronic combination lock with key

After starting the program asks to enter the decimal value of the code in the range from 1 to 254 inclusive. Enter a value, for example, 200. After pressing the program prints on the printer the key template and the pin numbers of the X1 connector, which must be connected with jumpers. The template printed in this way is cut out and glued onto a metal blank. The "+" sign marks the centers of the holes. The letter X marks the hole that should be at the bottom of the key when it is inserted into the well. It is convenient to pass a metal ring with ordinary keys through it.

The shift signal arrives at the input C of the DD3.1 register with a very small delay relative to the arrival of the signal at the input D, which can lead to fuzzy operation of the key. To increase this delay between the output of the DD2.1 element and the common wire, it is useful to include a capacitor with a capacity of several hundred picofarads. Inverter DD2.2 in this case is best used with hysteresis (DD1.4).

Author: S. Rychikhin, Pervouralsk, Sverdlovsk region

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