Audible alarm apparatus particularly adaptable for use with fire and theft security systems

摘要

The alarms circuit provides a first signal indicative of a fire alarm and a second signal indicative of another intrusion such as a burglary. The circuit includes a high frequency RC oscillator which undesireably possesses a duty cycle different from fifty percent. The oscillator output is divided by a bistable multivibrator to produce at an output, a divided signal having a fifty percent duty cycle for application to a loud speaker to energize the same efficiently due to the proper duty cycle. In a burglary mode, the oscillator frequency is modulated by a sawtooth developed by a second bistable multivibrator to provide a wailing tone signal indicative of a burglary. This signal is also divided to produce a proper duty cycle signal for application to the loud speaker.