This circuit was found in an English publication from the 70s, an article that teaches how to calculate instruments. The circuit is still current and can be built with an analog indicator of 100 uA.
This optically coupled circuit was found in the February 1968 Radio Electronics magazine. The...
This is the receiver for the CB17133E. Its main feature is that it uses only transistors. The...
This circuit, from the 1990 Motorola Dataar Databook, can use any LM139 series comparator. The circuit...