Found in Popular Electronics from the 90's, this tuned to infrared modulated receiver uses a PLL. The circuit has a signal strength indicator.
This circuit is a driver for R-2R network of AD converters. We found it in manufacturer...
This circuit was found in an American publication from the 60's. The transistor is made of...
This circuit produces an audio tone on the speaker or magnetic capsule. Rx must be such that added...