This circuit was published in the July 1993 issue of Electronics Now magazine. It uses a sensor from the time and triggers a buzzer with a Sonalert-type oscillator.
The LDO series (Low Dropout) TPS80 from Texas Instruments (www.ti.com) can provide output voltages...
The presented circuit uses an operational one of the time. The circuit is from an 80's manual and...
The operation of this circuit is old, but the configuration can be elaborated based on modern...