Octopus Tester.

This circuit dates back to at least 1935 and is a simple cheap adapter that converts just about any oscilloscope into a component tester. It causes a component's current vs. voltage characteristics to be displayed on an oscilloscope's screen. The name "Octopus" is attributed to a Marine Corporal who reinvented it in 1968 while working working on Tactical Navigation Systems at NAS Newriver, NC. He called it "The Octopus" "...because the first one was so messy with wires sticking out all over the place,..."

I made mine using an old 6v heater transformer, I was surprised just how  well it works. I can see it being one of the most useful bits of test gear in my shack.

Here are some photos of the traces on the scope.

this one shows a 4.7uf capacitor which gives an oval shape, depending on the size of the cap it could be a circle, the one here shows a 1uf cap .  This line shows a 1k resistor

and this one a 10k resistor.

A vertical line shows a dead short, there are other shapes for diodes, zenors and it is a great transistor checker. Also makes it easy to ckeck FET’s and Mosfets.