Once you are building electronics projects, the ability to take a look at what is going on in the real world is invaluable for troubleshooting. For this you really need an oscilloscope which are usually quite expensive. I found this kit that gives a low cost way of entering the world of electronics instrumentation.
I bought the version with the surface mount chips presoldered as they are tiny and I was careful to sort the components before starting.
I used my component tester to make sure that I was using the right components. Here it is working connected to the test signal.
You can power it from a small 9V battery making it very portable. While it only works up to 200kHz and the screen in tiny at 2.4 inches, that is plenty good enough for most projects and you can’t beat being able to see what is happening when you are building a project or writing some software that interacts with the real world.