This sensor circuit from a 1967 Ferranti documentation uses components from the era. The circuit can be used as a shield, although the integrated one used is unusual today.
We find this circuit in a 1970 publication. Transistors can be replaced by current equivalents and LDR is...
Featuring low output impedance and high input impedance, this configuration was found in a 1980s...
Found in a 1980s American documentation, this circuit can use a SCR and a general-purpose transistor....