Often when the words Homebrew Rigs are mentioned immediately the conjured view is one or two transistors, no dial readout and looks like chewing gum and bailing wire.
Actually, there are homebrewer's who build very polished and professional looking rigs that look like they were manufactured on a production line.
Many homebrew rigs are feature rich and include things like S Meters. Some are actual analog S Meters and some have taken the Arduino beyond LED ON, LED OFF and sport a Digital S Meter.
A good starting place for adding either type of meter is with the Rev George Dobbs G3RJV (SK) whose name is synonymous with the G-QRP Club. The link to his name is a series of articles called the Weekender Projects and one of those is an Audio Derived S Meter.
This now surfaces the subject at the weed level. There are the purists who argue the Audio Derived S Meter is inaccurate and/or inappropriate. The purists further argue for the IF derived signal as that more represents what is actually coming through the ionosphere. Wes Hayward in one of his projects had an elaborate combo IF and Audio S Meter.
In my build I just used something similar to the last transistor stage (can't seem to find my schematic) but have a pot on the output to set the value going into the Arduino analog pin. Since I was sampling off of the pre-amp stage, I eliminated essentially what is the MPF102 part of the schematic.
At the time I wrote the sketch for the PSSST-20, I had thought about an S Meter, so it was a pretty simple transition to the final install.
Essentially, I sample the voltage on one of the Analog pins on the Arduino. This voltage is then math massaged with log functions and maybe a square root or two to provide, with the magic decoder ring a variable number. This number is the X axis travel of a small rectangle on the display. Thus, we have a Bar Graph type S Meter.
So, if you want to see a meter bounce around much like the Burlesque Queen Lily St, Cyr then this is a project for you.
73's
Pete N6QW