This switching circuit for analog signals is from a 90’s Electronic Engineering. The components admit equivalents.
This conventional astable multivibrator circuit with operational amplifier can be found elsewhere on...
The LDO series (Low Dropout) TPS80 from Texas Instruments (www.ti.com) can provide output voltages...
This circuit was found in a Hands On Electronics from the 80's. The circuit emits an audible alert...