Dual Channel Combination Lock

Encyclopedia of radio electronics and electrical engineering / Security devices and object signaling

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The proposed code lock has two independent outputs for controlling actuators. Each of them is activated by its "own" eight-digit code, which is set using two buttons.

The code lock is assembled on digital microcircuits of the CMOS structure and has low power consumption in standby mode, so it can be powered from an autonomous source, such as a battery. When you press any of the buttons while dialing the code, the device switches to active mode. The code is a combination of ones and zeros. Moreover, one button is used to set units, and the other - zeros. In standby mode, both outputs are logic low. To get a high level at the required output, which will turn on the actuator, you need to dial its code and press both buttons at the same time. As long as the buttons are held down, this output will be logic high. As soon as the buttons are released, the output goes low again.

To notify of an error when dialing a code, a low-power built-in sound signaling device is provided - this is the first level of signaling. It turns on when the code is entered incorrectly after pressing both buttons at the same time. After that, you have 15 seconds to retry dialing the code. If after this interval the correct code is not dialed, the device will give a signal to turn on the external security alarm and turn on the self-locking mode for ten minutes - this is the second level of alarm. After that, coding becomes impossible.

Fig. 1

Let us first consider the operation of the basic version of the lock, which has only one exit, its diagram is shown in Fig. 1. The dialed code is generated at the outputs of the shift registers DD3.1, DD3.2. On the edge of the pulse at the inputs C of these registers, the information from the input D is written to the first digit of the register and the information is shifted towards the most significant digit. The code is dialed with the buttons SB 1 and SB2, single vibrators on the elements DD1.2 and DD1.3 eliminate the possible bounce of their contacts. For a set of log. 1 press the button SB2, at the same time a low level is formed at the output of the element DD1.3, the transistor VT3 opens, the capacitor C6 is charged and a high logic level appears at the input D of the register DD3.1. After releasing the SA2 button, the DD1.3 element will switch to its original state, a high level will go to the inputs C of the DD3.1, DD3.2 registers and a log 3.1 will be written to the first bit of the DD5 register (pin 1), since the capacitor Sat will not have time to discharge through resistor R13 to a low voltage.

For the next set of log. 0, you must press the button SB1, while the output of the element DD1.2 will appear low. The transistor VT3 is closed and the capacitor C6 is discharged, so the input D of the register DD3.1 will be low. After releasing the button SB1 log. 0 will be written to the first bit of the DD3.1 register (pin 5), and the log that was there before. 1 will move to the second digit (pin 4). And so on, until all eight digits of the code are written, while the first digit dialed will be at output 4 of register DD3.2, and the last one at output 1 of register DD3.1. For the device according to the scheme in Fig. 1 code 10001101 is set. Only after it is set at the connection point of the cathodes of the VD10-VD17 diodes will a low level appear, which will go to one of the inputs (pin 6) of the DD2.2 element. But this element cannot switch, since at its second input (pin 5) there is a high level coming through the diodes VD3, VD5 from the outputs of the elements DD1.2 and DD1.3. And only when both buttons are pressed simultaneously, the high level will change to low and the DD2.2 element will switch - a high level signal will appear at the lock output, the VT4 transistor will open and the HL1 LED will light up. As long as both buttons are pressed, the lock code at the outputs of the registers does not change. After releasing the buttons, the information will shift and the code will automatically become incorrect, so there is no need for a special button to reset the dialed code.

It follows from the diagram that the log. About in the code at the output of the registers corresponds to the diode, and the log. 1 - inverter and then diode. Therefore, any desired code can be set by connecting either a diode or an inverter with a diode to the outputs of the registers.

Since in standby mode there is a high level at the outputs of the elements DD1.2, DD1.3, as well as on the cathodes of the diodes VD10-VD17, to prevent the flow of current through the resistors R7, R8, the elements DD2.1, C2, R3 and the transistor VT2 are introduced. Transistor VT2 in standby mode is closed, and capacitor C2 is discharged, so the inputs of the element DD2.1 are low, and its output is high, and the current does not flow through resistors R7 and R8. When you press any button, the transistor VT2 opens, the capacitor C2 is charged to the supply voltage and a low level is set at the output of the element DD2.1. This is how preparation for switching element DD2.2 is carried out. After the button presses stop, the capacitor C2 will begin to discharge through the resistor R3 and after a while the DD2.1 element will switch - a high level will be set at its output and the device will go into standby mode.

If an incorrect code is entered and both buttons are pressed, one input (pin 2) of the DD1.1 element will be low, since the DD2.2 element will not switch. The second input (pin 1) of the DD1.1 element will also be low, so its output is low. Transistor VT1 will open, followed by VT5, and the supply voltage will be supplied to the acoustic emitter HA1 with a built-in generator. An audible signal informs that the code is entered incorrectly. At the same time, capacitor C7 is charged through diode VD8, and capacitor C18 is charged through resistor R9. After 15 s, the voltage on the capacitor C9 reaches the switching threshold of the element DD2.4 and the high logic level at the "Alarm" output will change to low - the HL2 LED will light up and the external burglar alarm will start working, activated by a low logic level. A high level from the capacitor C9 will go to the input R of the register DD3.1, and the code set becomes impossible until the capacitors C8 and C9 are discharged through the resistors R17 and R18. With the ratings indicated in the diagram, this will take about ten minutes. If the code is entered correctly, the transistor VT1 remains closed and the external alarm will not turn on. Capacitors C1, C3 are introduced to protect against interference in the power circuit, they should be located, if possible, closer to the power outputs of the microcircuits.

Fig. 2

By making small changes to the circuit, it is possible to independently control the two outputs. These changes are shown in Fig. 2. Logical element 2OR-NOT DD2.2 (see Fig. 1) is replaced by two elements ZIL-NOT DD5.1 ​​and DD5.2 (Fig. 2). The cathode of the VD10 diode is not connected to the cathodes of the VD11-VD17 diodes, but is connected to the input (pin 2) of the DD5.1 ​​element, and the output 1 (pin 5) of the DD3.1 element through the VD18 diode is connected to the input of the DD5.2 element. Now the old code 10001101 can be used to control "Output 1" of the lock, and the code 10001100 - "Output 2", otherwise the operation of the device remains the same.

Fig. 3

The presence of two outputs significantly expands the capabilities of the device. With their help, you can control two independent mechanisms, for example, electromagnets or electric motors to open a door lock, or reverse one mechanism. And finally, two exits make it possible to fundamentally complicate the code, increasing its secrecy. An option to refine the circuit with a sixteen-bit code and one output is shown in Fig. 3. The algorithm for opening the lock is as follows: dialing the first part of the code (eight digits), pressing both buttons (the VT6 transistor will open and charge the capacitor SU, and a high level will go to the first input of the DD4.3 element), dialing the second part of the code, pressing both buttons. A high logic level will go to the second input of the DD4.3 element, it will switch, and a high level will also appear at the output of the DD4.4 element. After some time (about 10 s), the capacitor SU will be discharged through the resistor R23, and the device will return to its original state. The number of digits in each part of the code can be reduced to the desired one by appropriately simplifying the circuit.

A few words about the possible location of the buttons. Since there are only two of them, there is no need for visual control when entering the code. This allows you to place them in "secret" places, for example, under the driver's seat in a car, under a table top, in a wall niche, etc.

The device is assembled on a breadboard using wired wiring. Power supply is carried out from a battery with a voltage of 9 V - 6F22 or from the vehicle's on-board network. Resistors MLT, S2-23 are used, the resistor R17 is composed of two 2 MΩ each connected in series Oxide capacitors - imported or K50-35. the rest - KYU-17. Transistors KTZYu2B and KT3107B are interchangeable, respectively, with transistors of the KT315 and KT361 series with any letter indices, diodes KD521A - with KD103B. KD522B, an acoustic emitter with a built-in generator, you can use any one with an operating voltage of 12 V. LED HL1 - any green glow. HL2 - red, preferably with increased brightness.

Establishment comes down to setting the time intervals for blocking and delaying the activation of an external alarm at will. You just need to keep in mind that they are interconnected and the resistance of the resistor R18 should be approximately ten times less than the resistance of the resistor R17, and the capacitance of the capacitor C9 is ten times less than the capacitance of the capacitor C8. A selection of these resistors and capacitors can change the specified time intervals over a wide range.

Author: V. Strukov, Voronezh; Publication: radioradar.net

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