Electronic code lock. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Electronic code lock. 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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The lock is designed to protect residential and service premises from unauthorized access. Its feature is the unusual input of code numbers (by repeated pressing of the buttons), which increases the "secrecy" of the lock.

The lock is easy to operate, does not require adjustment, and is not critical to the parameters of the power source. In standby mode, it consumes very little power. The lock is protected from unauthorized access by the use of pulse counters (10 combinations) and the introduction of a timer that limits the code dialing time.

The lock scheme is shown in the figure. According to the functional purpose, the device can be conditionally divided into four parts. The first is a code set block (elements DD1, DD3-DD6, DD7.1); the second - elements for resetting counters and a timer (DD2.1-DD2.3, DA1); the third part is the executive (elements DA2, VT2, VS1, K1) and the fourth is the power supply.

Electronic code lock

With a short press of the SB5 button, the counters DD3-DD6 are set to zero and the timer DA1 starts. Subsequent presses of this button do not affect the operation of the timer, but allow you to reset the readings in case of an error in dialing. The code must be set in time t=1,1xR11xC1, where R11 is the resistance of the resistor in megaohms, C11 is the capacitance of the capacitor in microfarads, t is the time in seconds. The resistance of resistors R11, R12 can be in the range of 10 ... 100 kOhm. After a time t at the output of the timer DA1 (pin 3) there is a low level and the counters are set to their initial state.

Code programming is carried out by soldering the corresponding jumpers. The code is dialed by pressing the corresponding button (SB1-SB4) a specified number of times. Let's assume that the lock code is set to 1952 (shown in the diagram). Then the first button should be pressed 1 time, the second - 9, the third - 5, the fourth - 2 times. The buttons are connected to the counters through the triggers of the DD1 chip, which allow you to eliminate contact bounce.

If the dialed code matches the code specified by the jumpers, a low level occurs at the output of the DD7.1 element and the timer DA2 starts, which determines the duration of the lock opening. The delay of the lock in the open state is especially convenient if the type-setting field and the actuator are at some distance from each other. When the timer starts, a high level occurs at pin 3 of DA2. The signal is amplified by the current emitter follower VT2 and through the resistor R15 is fed to the control electrode of the thyristor VS1. The thyristor opens, relay K1 is activated, starting the actuator (electromagnet, etc.). At the end of the pulse generated by DA2, a low level occurs at the output of the timer and the thyristor closes, turning off the actuator.

The timer DA2 can be excluded (respectively, it is necessary to exclude the elements C3, C4, R12), and the left output of the resistor R13 according to the diagram can be connected to the output of the element DD7.2. In this case, the lock opening time is defined as t minus the code dialing time.

The power supply is built according to the standard scheme. Diode VD1 separates the power circuits of microcircuits and relay K1, which is powered by pulsating current. This is necessary so that the thyristor VS1 closes when the control signal stops. The use of CMOS microcircuits allows you to power the device with a voltage of 5 to 15 V (selecting the Zener diode VD3 accordingly).

The device uses K176 series microcircuits. Instead of IE8 counters, you can use IE9 counters, but then the number of code combinations will slightly decrease. Resistors - any, capacitors - KD, KM, K10-17, etc., oxide - K50-29 or similar. Thyristor VS1 - KU221 with any letter index.

Author: S.Bashirov, Izhevsk

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