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 twilight switch or pass switch was obtained from a 1967 Philips documentation. The circuit...
This high-Q low-pass filter was found in the October 1990 issue of Radio Electronics magazine. The...
This circuit was obtained in an American documentation from the 80's. The transistors can be...