This 1970 Electronic Design circuit uses a varactor or varicap. The circuit divides the frequency of a 150 MHz signal by 2. Similar versions appear on this site.
This is yet another simple LED driving game circuit that appears in several other versions on this site....
We found this circuit in a manual of optoelectronics from Texas Instruments. In it photodiodes or...
This interesting circuit is from a 1988 documentation. It is a matrix of diodes that converts...