A-Star 32U4 Micro Programmable Module

I use this board as a breakout for the ATmega32U4, my new favorite microcontroller. It's a great platform to get started with USB applications. For example, take a look at my USB HID project here: http://www.radiandynamics.com/tutorials/getting-started-with-avr-microcontrollers/12/ You can easily program the microcontroller using Atmel Studio and an AVR programmer, such as the AVR ISP mkII.

This is my new favorite! 5V and 3.3V all on the same board... plenty of pins... what's not to like.

This is an excellent choice when space in your project is limited. It has many input/output as an UNO board + 8 analog inputs , 2 more than an UNO. Easy to use , can be connected to the Arduino app and selecting Micro UNO. Just follow circuit board plan to use appropriate pin , you will need to double check to make sure to use and connect the right. Depending of your programme , same pin can have different setting . It worth having this mini board in your stock.