Found in Popular Electronics from the 90s, this circuit detects modulated infrared radiation and serves as a test for remote controls. Infrared sensors equivalent to the one indicated can be used.
This circuit was found in an 80's Electronic Design. It amplifies TTL fast signals for a coaxial...
This circuit maintains on a flashing LED at a frequency determined by the capacitor. The...
Found in 1965 Radio Shack documentation, this circuit has a crystal phone output in the 14.8 kHz...