I picked up a few of the Adafruit Atmega32u4 breakout boards for a workshop earlier this summer. These are great, inexpensive little devices, but they’re only intended for AVR development in C, not Arduino. Adafruit used to support running Teensyduino on these, but they don’t anymore, and my attempts to run Teensy on them were really buggy — using the Arduino serial library would cause them to crash, for example.

It turns out that using the Leonardo bootloader is much more reliable. Here’s how to get that set up:

1. Set up an external programmer. You can’t flash the bootloader on the breakout board over USB. You’ll need a separate ISP, or you can set up another Arduino as an ISP if you want (follow this tutorial)
2. Flash the bootloader. In the Arduino IDE, go to Tools > Programmer, and select the appropriate device. Go to Tools > Board and select Arduino Leonardo. Then click Tools > Burn Bootloader.
3. Update references. Changing the bootloader means your pin references in software won’t line up properly with your hardware. Compare the schematics (breakout board vs Leonardo), and address the pins as you would on a Leonardo, but connect them according to the atmega32u4 breakout board schematic. Since the breakout board has fewer pins than the Leonardo, naturally you can’t use the same range as the Leonardo documentation would tell you.

   Here’s a pinout diagram for the breakout board running the Leonardo bootloader. Thanks to Nikhil Lal.
   

If you really, really want to run Teensyduino, you can still find Adafruit’s documentation on how to set it up, and this forum thread might help fix problems. Again, they don’t recommend doing that, and I ran into a lot of trouble when using standard Arduino libraries.

Super Blinky is a better version of Blinky.

This tutorial introduces a few new concepts:
1) Pulse-Width Modulation (PWM), to fade the LED.
2) Analog-to-Digital Conversion (ADC), to read a potentiometer (variable resistor, used for analog encoding)
3) Communication using UART over a Serial-to-USB connection

Background knowledge: complete Blinky first.

1. Wire up the potentiometer. Run the outer leads to 5V and GND. The middle lead should be connected to the analog read pin — F7 on atmega32u4 breakout and F0 on teensy++. A potentiometer scales the voltage across the two outer leads by moving conductive material across an internal resistor. This scales the voltage by creating a variable voltage divider.

2. Move the LED jumper. Why a different pin? We want to use a digital IO pin that is PWM-enabled. Use pin D0.

3. Set up the serial connection.

   const int ledPin = 0;    // LED connected to digital PWM pin 3, 0 on teensy++
   const int analogPin = 0; // Potentiometer connected to analog pin 0
   
   int analogVal;
   int delayVal;
   int fadeVal = 0;
   boolean fadeUp = true;
   
   void setup()  { 
     Serial.begin(38400); // initiate serial connection at 38400 baud
   } 

   This initiates a serial connection at 38400 baud, or signals/second.

4. Implement dimming.

   void loop()  { 
     analogVal = analogRead(analogPin);
     
     delayVal = map(analogVal, 0, 1024, 1, 5);
     analogWrite(ledPin, fadeVal);           
     delay(delayVal);                            
   
     if(fadeUp) {
       fadeVal++;
     } else {
       fadeVal--;
     }
     
     if(fadeVal == 255 || fadeVal == 0) {
       fadeUp = !fadeUp;
     }
   }

   This code reads the voltage on the analog read pin (on a scale of 0-1024), uses the map() function to scale that range to 1-5, writes a brightness level to the digital PWM (LED) pin, delays an amount proportional to the read voltage, and changes the brightness level.

   Note: You don’t have to call pinMode() before using analogWrite.

5. Send data over serial.

   Serial.print("analog 0 is: ");
   Serial.println(analogVal);
   delay(1); //for stability

   Yes, it’s that simple.

6. Upload sketch, observe superior blinking. Twiddle with potentiometer knob.

   If nothing is happening, check pin assignments, test the LED connection by jumping directly to 5 V, etc. Make sure the right leads of the potentiometer are connected to the right things. There should be blinking regardless of the value on the potentiometer. Turning the potentiometer clockwise should result in faster blinking.

7. Listen over serial.

   Click “Serial Monitor” (magnifying glass icon) in the upper left corner of the Arduino IDE. The board will auto-adjust to the monitor’s baud rate, but if that doesn’t work for some reason, you can manually set it to 38400 baud (as it is in the sketch). You should see “analog 0 is:” lines appear every time the LED fade changes direction.

   This line contains the analog voltage relative to AREF (i.e. 5 V) on a scale of 0-1024, meaning the actual voltage read is (displayed voltage/1024)*(5 volts)

   Sometimes the IDE gets finicky with serial ports, if it complains try refreshing the serial port menu or unplugging/plugging in your board.

Next: Project Ideas

To run as a separate device:

Mess with the Teensyduino installation.

Technically, the atmega32u4 breakout board isn’t designed to work with Arduino. By messing with some configuration files in Teensyduino, we can set it up as device in the Arduino IDE and upload code directly. Note: This isn’t necessary to do if you are actually developing on a Teensy++, but it won’t hurt, and if you’re reading this before the workshop, you don’t know which device you’ll be working with, so just do this now.

In <arduino>/hardware/teensy/, rename boards.txt to boards_old.txt and replace it with the boards.txt from the workshop repo.

In <arduino>/hardware/teensy/cores/usb_serial/, rename usb.c to usb_old.c and replace it with the usb.c from the workshop repo.

where <arduino> refers to whatever directory you installed Arduino into. If you had the Arduino IDE open, close it and re-open.

Project ideas for you to work on for the rest of the evening. I have the parts for these, and there may or may not be some starter code in the “projects” directory of the repo. Just give it a shot, ask me for help. Let me know when you have picked a project from this list or thought of one on your own and I’ll give you parts.

• Lightsaber — Using this 3D accelerometer, build a lightsaber app. Have the microcontroller send data over serial to a script to generate lights/sound.
• Mini Synthesizer — Generate tones, play them on a speaker. Use PWM for simple beeps, do DDS for more complicated sounds.
• Spin Things — Play with a DC motor.
• Fun with LCDs (2 groups) — Make something cooler than the hackNY logo on LCD screens. 2 groups because I have a large breadboard with both a Nokia cell phone screen and a 16×2 character LCD screen wired in next to eachother.
• Blinky v3 — Use a bunch of LEDs to make cooler patterns.
• Arduinophone (2 groups) — Connect your boards together using the UART TX/RX pins. Have them talk to eachother by spitting out messages received over serial (or maybe just pings, to begin with). It’s like the modern-day equivalent of the can & string telephone.
• Programmable Electrician — Use a 120VAC relay (capable of switching on & off outlet power lines) and some extension cables I modified a while back to turn on or off any device with a plug using Arduino.
• Weather Station — Use a temperature and humidity sensor in combination with an LED as a primitive light detector, send data over serial
• Anything else you want that I have parts for

General tips:

1. Look up part datasheets. If you don’t know what a part is, find a part number on or near the device, Google it, find the datasheet which is all relevant information.
2. If there’s a short, cut the power immediately. THEN try to figure out what went wrong in your wiring.
3. Ask questions! I have experience working with all of these devices.