This circuit was obtained in an Electronic Design from the 80's. It has the adjustment of the gain through a simple potentiometer. The power supply must be symmetrical.
In the figure we show how to activate a relay from the output of a common operational amplifier when...
Found in a publication from the 50's, this circuit uses a germanium transistor of the time. The...
November 2016 - Mouser Electronics already has the Arduino Shield 101 for IoT applications with...