This circuit was found in the September 1989 issue of Radio Electronics magazine. The circuit uses components that support modern equivalents such as the operational amplifier.
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....