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 circuit was found in a Radio Electronics magazine from August 1963. The transistors are...
This circuit consists of an oscillator that applies the signal to a transformer in order to obtain...
This is a voltmeter with high input resistance. The transistor is germanium. We found it in an...