This tool is used to test capacitors. It is really easy to make, as only additional hardware needed (besides the capacitor that will be tested) is 2x220ohm resistors. The basic scheme is this:
I also made a shield that makes things easier, but it is heavily improvised and is not a recommended way to make one.
I will not provide explanation on how to make this one, as its made very poorly. Here I used 222ohm 3W resistors because they have more rigid legs then 1/4W resistors do, they are used to connect to the Arduino pins, do not do this, rather use a male header with extra long pins. I added a button to only momentarily measure capacitance, there is no need for it to be done constantly, even when the capacitor is not inserted. (Full schematic posted below)
The data is fed to the computer over serial terminal:
Here we can also add a LCD display and a battery, put it in a case and make it portable. This project was done because most cheaper multimeters do not have this feature implemented, so this is a cheap and simple solution to the problem.