This gas sensor circuit was found in July 1976 Radio Electronics magazine. The TGS sensor was a common type at the time. Note the power supply to the circuit.
This second-order filter was found in a documentation from the 90's. It can be implemented with...
To implement this function, we need a relay with double contacts, as shown in the figure. With a...
In this circuit the relay triggers on when light falls onto the sensor, a common LDR. Power supply...