This interesting circuit in which the LED display is circular imitating a common clock appeared in the Radio Electronics magazine of May 1977. The power supply is included.
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...