This circuit was found in February 1976, Radio Electronics magazine. The components are from the time and are based on the 555. The power supply must be provided with the indicated voltages.
We found this circuit in a 1990 documentation. The operational amplifiers are type 741 and the LED is...
We found this circuit on an Elektor from the 90s. The frequency is given by capacitor C1. The...
Found in National Semiconductor publication from the 1980s. This gain-100 circuit can be...