STEMTera (Arduino Breadboard) Tutorial

What is the STEMTera?

STEMTera was the first project that I have supported on KickStarter and the experience has been overwhelmingly positive. So what is STEMTera?

At its simplest the STEMTera is a breadboard with an embedded Arduino UNO. Most shields will plug straight in. But it is more than just a simple Arduino prototyping platform, it also includes:

• a LEGO® compatible bottom which allows you to mount it directly on your LEGO creation.
• An ATmega32U2 microprocessor which is exposed, users can develop native USB projects with an extra 21 IO pins. These extra IO pins can work directly with the LUFA framework. More on this below.
• Multiple IDE support including Atmel® Studio, Arduino IDE, AVR-GCC, AVR-GCC with LUFA, Scratch, etc.
• Embedded LED's to indicate Power on, Tx, Rx and and one connected to D13 for your own use.

The Arduino functionality is the same as for an UNO, plug the USB port into your computer and away you go. The ATmega32U2 functionality is new and deserves a bit more explanation.

ATmega32U2

The newer Arduino Uno boards have two programmable microcontrollers: one is ATmega328, which is the Arduino processor that you usually upload your sketches to, and the second is the ATmega16U2, which is flashed to operate as a USB to Serial converter.

The ATmega16U2 chip on the Arduino board acts as a bridge between the computer's USB port and the main processor's serial port. Previous versions of the Uno and Mega2560 had an Atmega8U2. It runs firmware that can be updated through a special USB protocol called DFU (Device Firmware Update).

As part of the STEMTera KickStarter campaign there was a stretch target which if met would result in the ATmega16U2 being upgraded to the ATmega32U2. This target was met and so the upgrade was incorporated into the finished product. Even better, the ATmega32U2 pins have been brought out to the breadboard so that you can utilise them.

By updating the ATmega32U2 firmware, your STEMTera can appear as a different USB device (MIDI controller, HID, etc.).

DFU Programmers

To update the firmware on the STEMTera ATmega32U2 you will need a DFU Programmer.

Windows: Download Atmel's flip programmer.

Mac: Install MacPorts: Once MacPorts is installed, in a Terminal window, type

sudo port install dfu-programmer

NB: If you've never used sudo before, it will ask for your password. Use the password you login to your Mac with. sudo allows you to run commands as the administrator of the computer

Linux: from a command line type

sudo apt-get install dfu-programmer

Enter DFU mode

To enter program (DFU) mode you need to short the ATmega32U2 ICSP reset pin to ground until the red LED starts to flash.

Flash the chip

Windows: use flip to upload the hex file to your board

Mac & Linux: from a terminal window, change directories to get into the folder with the firmware. If you saved the firmware in your downloads folder on OSX, then you might type:

cd Downloads/

Once there, type:

sudo dfu-programmer atmega32u2 erase

When this command is done and you get a command prompt again, say you want to reflash the original Arduino firmware (Arduino-usbserial-uno.hex), then you would type:

sudo dfu-programmer atmega32u2 flash Arduino-usbserial-uno.hex

Finally:

sudo dfu-programmer atmega32u2 reset