Launching of an Arduino / Raspberry Pi Project!

Going back to the roots of this blog on this one!   When I am doing an electronics project my multi meter is constantly on my desk somewhere taking up part of my limited real estate.  So I put it away only to need it a few minutes later!  So the thought occurred to me...why not build a multimeter that is small enough to stay on my desk (or even behind it with only the test leads on the desk)?  And since it is now hidden behind my desk it will need to have a remote display...so how about having that display on the computer in front of me?

So is born this project:  Create a multimeter that can measure voltage (DC only, zero to 30), resistance (zero to 100k), and amperage (0 to 500ma, .5ma resolution).  My platform is going to be, you guessed it, an Arduino married to a Raspberry Pi:

The Raspberry Pi that I am going to use is the new Zero shown on the upper right.  I had planned on using the Onion Omega on the left but I want to do my User Interface app in Node.js and getting it setup on the Onion was a hassle.  The Arduino that I will use is the smallest in the family (of the versions on a PCB) and is the Micro Pro shown lower right.

My original plan was to use the below schematic as the electronics for my multimeter.  It is from this instructable, and as you can see, it is pretty complicated:

That complexity does buy a number of features that I don't need and some accuracy beyond my needs as well.  The majority of the time when I will need my new multimeter is for a simple continuity test, or to see if I have power and whether it is 3, 5, or 12v.   My needs are simple enough that I could probably do a tester just using an Arduino but that would not be as much fun as what I am planning.

Anyway...the electronics that I plan on implementing are less complicated than the above and will be based on this discontinued Sparkfun kit:

I am going to add a couple of switching transistors to get the number of probe connections down to three as max.  I guess the project will be wrapped up in a little 3D Printed case!