Electronic door lock combination - requires single key entry to terminate code and generated alarm signal with incorrect code

摘要

The combination lock system uses a keyboard and encoder but has the additional feature that the code entry must be followed with a further single key entry, the 'OPEN' code, and that an incorrect entry generates an alarm signal and disables the electronics for a specified period. The entire circuit fits into a wall switch recess. The keyboard (T) has an additional 'OPEN' key (O) which provides one input to two NAND-gates. The second input to the NAND-gates is the output from the key decoder integrated circuit. If this output is positive it will enable the first NAND-gate which triggers a monostable. The action energises the door relays. If it is negative, it will produce a negative going pulse from the second NAND-gate (G2), to trigger the second monostable (M2), resulting in an alarm signal (E).