Simple Code Lock

The above cycle is therefore repeated only when S7 at the Q1 output is pressed in time. When all keys have been pressed in time and in the correct order, Q7 goes 5 high for about 4 seconds to enable driving the unlock circuitry, e. g. a relay driver for an j automatic door opener. At the i heart of the circuit is the `Type 4022 octal counter. In th
Simple Code Lock - schematic

e non- active state, Cz is charged via R5, so that the reset (R) input of the counter is kept logic high. This causes output Qc to be actuated, while all other outputs are logic low. When S1 is pressed, T1 is switched on via debouncing network Rz ”C1, and IC1 receives a clock pulse. Also, Cz is discharged via R4-D1, ending the reset state of the counter and enabling it to I advance. The 5 code for the lock shown in the T circuit diagram is 1704570: this is but an example, however, and i the combination code is readily Y altered by swapping connections between the counter out- puts and the switches. This means that the number of combinations is 109 instead of 107. The quiescent current consumption of the code lock ` negligible at 0. 5 JA, so that the operation is feasible. The circuit works well from any supply between 6 and 15V

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