This circuit was found in a 1968 RCA documentation. The circuit can be designed with operational equivalents. Input signals can be up to 6 V in amplitude and the limitation is 78 dB.
This high-sensitivity circuit was found in a 1980s documentation. The source can be a 9 V battery...
This circuit was found in an American documentation from the 60's. The transistors are from the...
With an op amp with FET, this 1977 circuit uses an LDR as a sensor and drives a relay. The relay...