I bought an Uno and tried doing a MIDI controller but soon realized I need at least two other pieces of software to make the MIDI connection work. Is this the opposite for the Leonardo? I can just "plug and play" with it as a MIDI device?
The only software that's pre-programmed into the chip is the bootloader.
Search for leonardo midi library and leonardo midi projects
the library should have MIDI support and basic example sketches.
The Leonardo (or Pro Micro) is good for MIDI over USB. It needs no additional HARDWARE when a UNO would. But if you want to use traditional 5-pin MIDI then you still need extra hardware.
In either case it still needs to be programmed to do whatever you need i.e. it needs software. Arduinos don't come with complex software already built in.
Steve
There are a lot of examples for how to use the USB-AVR boards be standard USB HID devices the PC sees as mouse, kb, stick and also can appear as USB MIDI devices.
PJRC.com made the Teensy before the Leonardo or Micro became available. The Arduino boards use PJRC software AFAIK.
https://www.pjrc.com/teensy/td_midi.html
When you select "MIDI" from the Tools->USB Type menu, the Teensy becomes a USB MIDI (Musical Instrument Digital Interface) device, capable of sending and receiving MIDI messages. Teensy 2.0, Teensy++ 2.0, Teensy LC and Teensy 3.0 to 3.6 are supported.
MIDI can be used for non-music applications, such a controlling a large number of lights from a PC. Environments like Puredata and Max/MSP can give you access to MIDI for almost any purpose. MIDI is optimized to simultaneously transmit and receive large numbers of short messages with minimal delay.
Teensyduino implements a "class compliant" MIDI device, which can work with the built-in drivers on all major operating systems. When MIDIx4 or MIDIx16 are selected, Teensy implements a class compliant device with 4 or 16 virtual cables/ports.
There are guides to modifying Unos to run as HID with just a little hardware modding and special code.
GoForSmoke:
There are a lot of examples for how to use the USB-AVR boards be standard USB HID devices the PC sees as mouse, kb, stick and also can appear as USB MIDI devices.PJRC.com made the Teensy before the Leonardo or Micro became available. The Arduino boards use PJRC software AFAIK.
Teensyduino: Using USB MIDI with Teensy on the Arduino IDE
There are guides to modifying Unos to run as HID with just a little hardware modding and special code.
thanks, yes I found the program to make that happen. I suppose my next question is, I plan on using 4, 16 channel multiplexers, 2 for digital, 2 for analog. If I am not mistaken, that means they will use 5 channels each. Therefore i'd need 10 analog and 10 digital. Is this possible on the Uno, or do I need a Leonardo?
" If I am not mistaken, that means they will use 5 channels each. "
I don't know why 5 and don't much care really. Never messed with the hardware except consumer level. Sorry.
GoForSmoke:
There are guides to modifying UNOs to run as HID with just a little hardware modding and special code.
Note that this means real UNOs!
Not fake UNOs which are falsely advertised as they do not have the actual 16U2 chip and are thus, not UNOs at all, but only mutants of the earlier Duemilanove with a CH340 USB interface chip.