This circuit was obtained in a documentation from the National Bureau of Standards of 1968. The circuit is of low current and the output can be changed to voltages between 2 and 30 V.
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....