This traditional configuration with the 555 was obtained in an 80s Hands-On Electronics. The relay is of the sensitive type according to the supply voltage.
This circuit, found in documentation from the 1980s, uses an operational amplifier from that time....
This low frequency sinusoidal oscillator was obtained in documentation from the 1970s. Operational...
This circuit was found in a 1980s documentation. It is intended for remote vibration monitoring...