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 simple circuit controls the signal amplitude through a photoresistor optical coupler. The...
In the figure we have the way to obtain the Exclusive-OR function with 1 transistor. The circuit...
This circuit uses as an indicator a common micrometer type VU with 200 uA of full-scale current. The...