Found in Precision Monolithics documentation from the 90's, this circuit equalizes octave signals determined by the capacitor values according to the table next to the diagram.
The frequency of this circuit is approximately 1 Hz. Whenever the output is at low level, the LED...
This circuit can be used in a digital measuring or shield interface. The circuit is from old...
In the figure we show how to implement a TTL photo-trigger with the 7413. This circuit can be used...