This low frequency oscillator circuit was found in an Electronic Design from the 90s. The transistors are common types, and the frequency is given by the crystal.
This circuit was originally created to monitor signals from a remote-control transmitter for the...
In this circuit the CA3140, an operational amplifier, is used as a comparator with the zener diode...
This circuit was found in old documentation. The frequency depends on R1 and C1. For the...