Got the PCB size and layout of the VU meter layed-out.
This will mate with the holes on the IO-module, just need to use a 3/4" standoff. So it will be like a double-decker.
I abandoned the idea of flipping the board upside down to go from horizontal to vertical progression of the VU meter. There's no more space on the IO-module PCB for additional holes.
Instead, I used jumper switches. There are 4 jumper switches. So the VU meter board will display properly whether mounted horizontally or vertically.
If mounted horizontally, the LED lights up as 1, 2, 3, 4, 5. (i.e. left to right)
If mounted vertically, the LED lights up as 5, 4, 3, 2, 1 (i.e. bottom to top)
This VU meter has been tested on a breadboard and works great.
Believe it or not, there is an on-board regulator on this VU meter board. The VU meter board can be powered anywhere from 5V to 18V. (Actually more than 18V, since it will be just regulated down to 18V if the input voltage is more than 18V.)
There is a trimmer to calibrate the 0dB mark (i.e. the 3rd LED) to your system.
Only requires 3 connections for the VU to work... V+, Gnd and Audio Input.