This circuit is used to detect PLL signals from the 4046 IC. The circuit is from an Electronics Now from October 1994. The indication is made through LEDs.
This TTL dice was found in an old American 1980s documentation, but can still be easily assembled....
This circuit for several frequencies was obtained in an American documentation from the 90s. The...
November 2016 - Vishay's new proximity sensors VCNL4100 for display presence and activation,...