With this circuit it is possible to visualize the characteristic curve of a component on an oscilloscope. The circuit is from a Popular Electronics from the 90s.
The function generator XR2206 is not very easy to obtain, but if you get one you can assemble this...
This 1990 circuit can also be used with fixed sound systems. What it does is trigger a set of LEDs...
In the figure we have a sensor circuit that makes use of common transistors and a photo diode as...