Repetitive alarm trigger circuit - uses capacitor charging and discharging through different resistors to control repetitive timing

摘要

The repetitive alarm trigger circuit is designed for the protection against breakin of premises. The alarm circuit is triggered by the closure of a contact which puts into operation a first timing interval between two alarms. At the same time a second alarm duration timing interval is actuated. The first time interval is obtained from the change time of a first capacitor change through a first resistance. The second time interval is obtained from the discharge time of this first capacitor through a second resistance. The first resistance forms parts of a change circuit consisting of a first transistor which closes the circuit when the transistor is conducting. The second resistor forms part of a circuit which is closed during the alarm period.