This configuration similar to many of this site was found in 1965 General Electric documentation. Modern equivalent transistors can be used. LEDs can be used.
This circuit for old photo enlargers was found in a 1970s RCA manual. The components are from the...
With an ultra-low consumption, this circuit can be powered by solar cells. The circuit is from a...
This is one of the many applications of the 555. We found it in the November 1992 Radio...