This circuit was obtained in an Electronic Engineering of the 90s. The operational amplifiers and the sensor are from that time. The circuit has symmetrical power supply.
This circuit, which in our times would be called a shield, can also be used with other loads. The...
This circuit is from an old American documentation from the 70s. Transistor 2N3904 can be replaced by...
This application of the 555 was found in the November 1992 Radio Electronics magazine. The...