This circuit is from a National Semiconductor manual from the 1980s. The integrated circuit is rare today and next to the diagram we have the formula for calculating the components.
This Rytron transmitter was published in a 1953 book. The circuit can be implemented with a BC558...
Foto-Darlington for applications such as light sensor. In normal applications only the collector and...
This circuit was found in a 90s Popular Electronics. It generates tones given by the oscillators and...