This circuit is suggested by Motorola in its 1990 Linear Databook. The integrated circuit is no longer common in the market.
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....