This simple logic level tester was found in Radio Electronics from the 90s. The inverters are of the 4009 type and the power comes from the circuit being analyzed.
The trigger element of this circuit is a neon lamp. The SCR admits an equivalent. We found it in...
This bistable with transconductance operational amplifier was found in early National...
This 1965 circuit consists of a small inverter for an ultraviolet lamp. The circuit is from a...