Using the LM3909 this circuit was found in the January 1992 issue of Radio Electronics magazine. Resistor R1 should be chosen according to the table given next to the diagram.
Found in a 90s American documentation, this circuit mimics the Enterprise warning signal from the...
The diagram shows a simple way to adjust a 7805 to have output voltages up to 12 V. The circuit is from...
The operational amplifier used in this configuration is of an uncommon type today. The circuit can be...