With this circuit of a Popular Electronics from the 90's it is possible to test a diode with the oscilloscope visualizing its characteristic curve. The transformer can have currents starting from 100 mA.
This circuit has a logarithmic response as a function of the light falling on the sensor. The...
This circuit was found in documentation from the 70s. The transistors are from that time, but the...
The idea is simple: using a flashlight to cut your TV commercials triggers a relay that turns off...