This circuit is from Motorola's Linear Interface ICs from 1993. The MC1723 is the equivalent of the well-known 723. The transistor supports equivalents.
The frequency of the sound emitted by this circuit depends on the light intensity on the sensor....
This circuit is from a thyristor manual from On Semiconductor. It makes use of a PUT and a SCR...
This circuit uses only one NC75Z04 port from ON Semiconductor, but it can be implemented with...