This circuit was found in an American documentation of the 90s. Optical resources with the LDR as a lens can help in obtaining directivity and sensitivity.
We found this circuit in an American 80's documentation. The circuit can be adapted to function as a...
This 80's circuit, suggested in Texas Insrtruments documentation, uses a Hall effect sensor. The...
This interesting benchtop circuit was found in the May 1977 issue of Radio Electronics magazine. The...