This alarm goes off if someone leaves a door open. We found it in the Encyclopedia of Electronic Circuits Volume 5 from 1995. The circuit uses components that are still common today.
This amplified circuit was found in a magazine for radio amateurs 73 of the 90s. The circuit uses an...
We found this circuit in a 1980s publication on espionage. The transistors support modern...
This 6-transistor receiver was manufactured in Japan in the 60s. The circuit is superheterodyne and has a 6V...