Control circuit for alarm system - has two time delays controlling initiation and termination of alarm signal

摘要

The electronic control circuit which is unlatched by a change in logic level of an input instruction signal includes a clock (3) providing a continuous pulse train, and a counter (9) receiving the clock pulses. A first NAND-gate (12) receives at its input (14) the instruction logic level signal, while its output (15) is connected to the counter (9) in order to start the counter when the level changes. A second NAND-gate (16) has one input (17) connected to the instruction signal, and the other input (18) connected to the counter output. A bistable circuit (20) is connected to the output of this gate in order to undergo a change of position when the second gate changes. A monostable circuit (28) having a predetermined recovery time is connected to the output of the second NAND-gate and to the bistable circuit.