This circuit was obtained in a Hands-On Electronics from the 90's. The circuit turns on one LED at the end of the timer, erasing the other. The timing can be increased by changing C1.
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...