Using an integrated circuit that was available at the time, this circuit produces animal sounds such as mooing, rooster crowing, etc. The circuit is from a March 1997 Electronics Now magazine.
This circuit is from Popular Electronics of the 90's. It makes use of NO and NC sensors. The relay...
Based on TTL logic this circuit can vary both the frequency and the pulse width of a rectangular signal....
This circuit was found in an old English publication. The circuit makes use of general-purpose transistors....