This circuit of a Popular Electronics from the 90s makes use of components of the time. The circuit has sampling and retention capabilities and a conversion rate of 1V / kHz.
This 80's circuit, suggested in Texas Insrtruments documentation, uses a Hall effect sensor. The...
This circuit, from a publication of the 1970s, can compare the intensity of two light sources,...
This circuit uses a photocell as sensor and a sensitive relay according the power supply voltage....