Simple Code Lock circuit

The circuit described here is of an electronic combination lock for daily use. It responds only to the right sequence of four digits that are keyed in remotely. If a wrong key is touched, it resets the lock. The lock code can be set by connecting the line wires to the pads a, b, c, and d in the figure. For example, if the code is 1756, connect line 1 to a, line 7 to b, line 5 to c, line 6 to d and rest of the lines2, 3, 4, 8, and 9to the reset pad as shown by dotted lines in the figure.
Simple Code Lock circuit - schematic

The circuit is built around two cd4013 dual-d flip-flop ics. The clock pins of the four flip-flops are connected to a, b, c, and d pads. The correct code sequence for energisation of relay rl1 is realised by clocking points a, b, c, and d in that order. T

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