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.
I found this circuit in an English magazine from July 1982. The circuit is still viable as all...
By adding a transistor to the output and some polarization features we can obtain a higher output...
This circuit converts negative logic signals to positive logic signals. We found it in 1969...