LilyPad Arduino USB: Wearable and Flexible Microcontroller

The LilyPad Arduino USB is a unique microcontroller board designed by Leah Buechley and further developed by SparkFun Electronics. It's part of the Arduino family, specifically engineered for integration into textiles and wearable projects. Unlike traditional rigid PCBs, the LilyPad features a small, round form factor with large, sewable copper pads instead of pins, making it ideal for embedding directly into fabric. This allows makers to create interactive clothing, accessories, and art installations that are both functional and aesthetically integrated.

At its core, the LilyPad Arduino USB is powered by the ATmega32U4 microcontroller. This chip is notable for its integrated USB controller, which eliminates the need for a separate USB-to-serial converter chip (like the FTDI chip found on many other Arduinos). This integration simplifies the board's design, reduces its size, and allows for direct USB programming and communication, a significant advantage for wearable projects where space and complexity are critical concerns.

The LilyPad Arduino USB sits in a niche within the Arduino ecosystem, focusing on flexibility and wearability. While it shares the ATmega32U4 with boards like the Arduino Leonardo and Micro, its physical design is distinctly different. Its sewable nature makes it a favorite among fashion technologists, artists, and hobbyists looking to add electronic interactivity to physical objects. The board is designed to withstand the rigors of being sewn into garments, though care should still be taken to protect sensitive components from excessive moisture or physical stress.

Released around 2012, the LilyPad Arduino USB was a significant step forward for wearable electronics, offering a more robust and user-friendly solution than previous attempts. It democratized the creation of interactive textiles by providing a platform that was both easy to program using the familiar Arduino IDE and simple to physically integrate into projects. This board is particularly suited for makers who want to experiment with e-textiles, interactive art, and small, flexible electronic devices where traditional boards might be too bulky or rigid.

Watch

Related video, embedded from YouTube.

Specifications

Pinout & pin functions

Wiring & circuit basics

Powering the LilyPad Arduino USB requires careful consideration of its operating voltage and power sources. The board is designed to run at 3.3V logic levels. It can be powered via its USB port, which will supply approximately 5V. Alternatively, a single-cell 3.7V LiPo battery can be connected directly to the BAT pad. The onboard 3.3V regulator will then supply power to the ATmega32U4 and other components. When connecting external components, ensure they are compatible with 3.3V logic. Connecting 5V devices directly to 3.3V pins can cause damage.

When connecting peripherals, always use the VCC pad for 3.3V power output. For digital outputs, ensure they are rated for 3.3V or use a level shifter if connecting to 5V devices. For analog inputs, the ATmega32U4 has a 10-bit ADC, but the LilyPad Arduino USB's analog pins (A0-A5) are connected to its internal 12-bit ADC, providing higher resolution. Remember that the board's sewable pads are delicate; use conductive thread or wire for connections and avoid excessive tension or sharp bends.

A simple example circuit involves lighting an LED. Connect the anode (longer leg) of an LED to a digital pin (e.g., D13, which also has an onboard LED for testing) through a current-limiting resistor (typically 220-330 ohms for a 3.3V system). Connect the cathode (shorter leg) of the LED to a GND pad. For an I2C sensor, connect its VCC to the LilyPad's VCC (3.3V), its GND to GND, its SDA pin to A4, and its SCL pin to A5. Ensure the sensor is also a 3.3V device.

Programming & getting started

The LilyPad Arduino USB is programmed using the Arduino IDE, just like most other Arduino boards. Since it features the ATmega32U4 with native USB, it enumerates as a standard USB Human Interface Device (HID) or serial port when connected to a computer. This means you don't need a separate USB-to-serial converter. To upload your first sketch, select 'Arduino Leonardo' or 'Arduino Micro' from the 'Tools > Board' menu in the Arduino IDE (as the LilyPad USB is not explicitly listed but shares the same microcontroller and bootloader). Connect the LilyPad via its USB port, select the correct COM port, and upload your code.

For more advanced users, the ATmega32U4 can also be programmed using other toolchains like PlatformIO, which offers a more integrated development environment and advanced project management features. CircuitPython and MicroPython are generally not directly supported on the ATmega32U4 due to its architecture and typical bootloader setup, which is optimized for C/C++ via the Arduino framework. Ensure you have the correct board drivers installed on your computer for the ATmega32U4 to be recognized.

Project ideas

Buying tips & gotchas