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Adafruit

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Note: The Pro Trinket's bit-bang USB technique is a legacy approach that may not work reliably with modern operating systems. For new projects, consider an ...

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Note: The Pro Trinket's bit-bang USB technique is a legacy approach that may not work reliably with modern operating systems. For new projects, consider an ItsyBitsy or Metro Mini board with native USB support at a comparable price.

The Adafruit Pro Trinket 3V is a compact ATmega328P-based microcontroller board that packs Arduino UNO-level capability into a 1.5" × 0.7" form factor. Running at 3.3V and 12 MHz, it's well suited for lower-power, lower-voltage projects. It's programmable via the Arduino IDE using the on-board USB bootloader or an FTDI serial connection.

Key Features

  • ATmega328P Processor – Same chip as the Arduino UNO; compatible with 99% of Arduino sketches
  • 3.3V Logic at 12 MHz – Lower power consumption for battery and voltage-sensitive projects
  • 18 GPIO Pins – Including 2 extra analogue inputs beyond standard Trinket (pins 2 and 7 reserved for USB)
  • 28 KB Flash / 2 KB RAM – 4 KB used by bootloader, 28,672 bytes available for sketches
  • Micro-USB Connector – For power and code uploads via USBtinyISP-compatible bootloader
  • FTDI Header – Alternative serial programming and debugging via FTDI cable
  • 3.3V Regulator – 150 mA output, up to 16V input, with reverse-polarity and thermal protection
  • Auto Power Switching – Automatically switches between USB and external battery power
  • Power and Status LEDs – Green power LED and red LED on pin 13
  • Reset Button – Enter bootloader or restart your program
  • Mounting Holes – For secure physical installation

Limitations

  • Pins 2 and 7 are reserved for USB and unavailable for general use
  • No Serial-to-USB chip — use an FTDI cable for serial monitor access
  • Cannot plug Arduino shields directly onto the board
  • 12 MHz clock speed may affect timing-critical libraries (NeoPixel library works fine)

Ideal For

  • Compact, low-voltage versions of Arduino UNO projects
  • Battery-powered and portable builds
  • Wearable electronics and small-form-factor installations
  • Prototyping before moving to a final embedded design

Package Contents

  • 1× Adafruit Pro Trinket 3V (assembled, without headers)

Jargon buster

Plain-language definitions for the technical terms used above.

3.3V regulator
A 3.3V regulator is a power circuit that provides a steady 3.3 volts for parts that need that supply voltage. On a breakout board, it can let the sensor run safely even when the connected microcontroller or power source uses a higher voltage.
ATmega328P
An 8-bit microcontroller chip used on many Arduino Uno-compatible boards. Knowing the controller uses an ATmega328P helps you understand its memory, speed, pin compatibility, and the Arduino sketches it can run.
Bootloader
Small starter software on a microcontroller that lets new code be uploaded before the main program runs. Knowing how to enter bootloader mode matters when you need to program the board or recover it after a faulty sketch.
GPIO
General-purpose input/output pins are microcontroller pins you can set in software to read signals, switch devices on and off, or connect to peripherals. The number of GPIO pins matters because it limits how many buttons, LEDs, sensors, and other parts you can wire directly to the board.
Headers
Rows of connector contacts on a fixed pitch (commonly 2.54 mm) used to link a board to a breadboard, jumper wires, or another board. They come as male pin headers and female socket headers; when a module ships with pre-soldered headers it can be used straight away, whereas bare pads require soldering the pins yourself.
IDE
Short for Integrated Development Environment, a program used to write, run and manage code. It matters because some learners prefer a traditional coding workspace instead of a guided notebook-style lesson.
LED
A light-emitting diode (LED) is a small electronic component that emits light when current flows through it in the correct direction. Because it only conducts one way, its polarity matters, and a through-hole LED must be soldered the correct way around to light up.
microcontroller
A microcontroller is a small computer on a single chip that runs a stored program and controls connected inputs and outputs such as buttons, sensors, displays and communication interfaces. In a device built around one, it is the part that executes the code and coordinates the device's behaviour.
native USB
Native USB means the microcontroller itself handles USB communication, rather than using a separate USB-to-serial chip. This matters for programming, debugging, and projects that need the board to act directly as a USB device.
NeoPixel
A type of addressable LED system where colour data is sent along a single digital data line from one LED or controller to the next. Compatibility matters because the timing and signal format must match for the lights or driver board to respond correctly.
RAM
RAM (random-access memory) is fast, temporary memory a device uses for working data while it is running; in its common volatile form, its contents are lost when power is removed. Some devices offer a mode that applies settings to RAM only, which is handy for testing changes temporarily because they are not stored permanently and disappear at power-off.
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