This circuit with germanium transistors was found in a publication by Gernsback from 1960. The circuit is low power, a few tens of milliwatts.
This circuit was found in documentation from the 90s. The components used are not common today. The...
This circuit was suggested by National Semiconductor in one of its manuals. The LM108 integrated...
This circuit was found in a 1987 magazine. It measures the pulse rate produced by a cardiac...