This 555-based circuit was found in the August 1976 issue of Radio Electronics magazine. The tone frequencies are provided by the capacitors connected to the 555 IC.
The given number circuit is used to activate the relay by interrupting the light beam that hits...
In the figure we have a simple and efficient way to obtain rectangular signals from an astounding 555...
This circuit, for 78xx series integrated devices, is suggested by Motorola in its 1990 Linear...