This circuit for very low frequencies was found in an American documentation from the 90's. Transistors are for general use and the frequency depends on C1 and C2.
This circuit is from an old documentation. However, it can be mounted with modern equivalent...
In the figure we have the way to add hysteresis to an operational amplifier. The relationship...
This video game is another of the AY3 series with the AY3-3606 integrated circuit. The circuit was found...