“Of the many possible microprocessor options, I like the teensy range best. These are (to my mind) Arduino done properly - they use the arduino language (and IDE if you want) by means of the 'teensyduino' add-on to Arduino software, but are very small, absolutely stuffed with peripherals (e.g. 58 digital IO, 25 ADC, 19 timers, multiple hardware serial, SPI and I2C ports running at 200 MHz or more) and have pins on a sensible (i.e. regular 0.1") grid.
Teensy 3.2 is one of the smaller (36mm x 18mm) of the 32 bit teensy range, running at 'only' 72MHz (though you can overclock it) and with 'only' about 40 I/O (but beware - some of those are on surface mount pads on the bottom of the board, so can be a little more tricky to utilise). It runs at 3.3V, but is 5V tolerant on most (not all) of the I/O, and has an on-board regulator so can be supplied by a bit more. It's my favourite in the range.
The only down side is that documentation could be better. To utilise some of that wonderful functionality you need to 'use the source' and read some of the published libraries, or plough through the teensy forums https://forum.pjrc.com for nuggets. It's worth the effort, though.”
