This circuit was found in an article in Electronics Now magazine from March 1997. The transistors are general purpose, and the indicator is a 1 mA full scale analog type.
This circuit with only one transistor was found in Japanese documentation from the 1960s. The...
This circuit uses a common multimeter on the voltage scale. The calibration of the scale should be...
This interface shield circuit is from the 1983 Intersil Databook. The components used are uncommon...