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.
This circuit was obtained from an English magazine from 1985. The N414 is a complete, not easy to...
Found on Popular Electronics from 1969, this circuit can be implemented with components that are...
This circuit is from a book of transistors from 1954. The transistors are from the time and the...