Arduino Pro Micro

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Pro Micro
Manufacturer Sparkfun (and others)
License Creative Commons Share-alike 4.0 International
Host port USB Micro B
Microcontroller ATMega32U4
MPU AVR (8-bit)
Voltage 3.3V or 5V
Clock speed 8 MHz or 16 MHz
Digital I/O pins 18
RAM 2.5 KB
Program memory 32 KB
Boot loader Caterina

The Pro Micro is an Arduino-compatible microcontroller board developed under an open hardware license by Sparkfun. Clones of the Pro Micro are often used as a lower-cost alternative to a Teensy 2.0 as a basis for a DIY keyboard controller/converter when a lower number of pins would suffice.


Like the Teensy 2.0, it sports an AVR ATmega32u4 8-bit microcontroller which has an integrated USB controller. It has a micro-USB type B port (Teensy 2.0: mini-USB), 18 I/O pins (Teensy 2.0: 25 I/O pins) and an integrated voltage regulator for 3V operation.

The Pro Micro is sold in a 3.3 V version (8 MHz) and a 5 V version (16 MHz).

On the 3.3 V version, shorting a solder bridge (J1) on the chip bypasses the 3.3 V voltage regulator on the board. This would allow 5 V operation and running at 16 MHz clock. At 3.3 V, the ATmega32u4 is otherwise limited to 8 MHz clock.

The ProMicro has three LEDs:

Colour Function ATmega32u4 port
red power on
yellow USB receiving data PB0 (active low)
green USB sending data PD5 (active low)


Arduino AVR AVR Arduino
USB port
TX D1 PD3 RAW (+5V from USB)
GND Reset
GND Vcc (+3V*)
SDA D2 PD1 PF4 D21 A3
SCL D3 PD0 PF5 D20 A2
A6 D4 PD4 PF6 D19 A1
D5 PC6 PF7 D18 A0
A7 D6 PD7 PB1 D15 SCLK
A8 D8 PB4 PB2 D16 MOSI
A9 D9 PB5 PB6 D10 A10
  • Two more pins are accessible by soldering directly to the bottom of the two lower most LEDs - the one above the P in the "Pro" label (beside the number 8), and the o in the "Micro" (beside the 1 of the number 16 in the image). These are Pins PB0 and PD5 of the AVR.

The pinout is nearly identical to the Arduino Pro Mini which has pin 3 as an additional Reset line instead of Ground.


Uploading native software to run on the Pro Micro works different than for the Teensy 2.0. There is no reset button on the board, instead two pins have to be shortcut twice to bring the device in bootloader mode for 8 seconds. While the Teensy comes with an graphical uploader tool, the Pro Micro is programmed using a command line tool called avrdude. Sparkfun's and scottc's tutorials explain this further (see links).


  • See the Pro Micro category for controller boards that are pin-compatible.
  • See the ATmega32U4 category for controller boards with the same microcontroller (but different pinout).

Beware that there are clones that differ from the original in incompatible ways:

Longer circuit board
Pin-compatible alternatives for the keyboard community may be longer for extra functionality, such as more pins, buzzer (for "click") and/or circuitry for a Bluetooth transceiver. They will not fit all keyboard PCBs.
Wider circuit board
Wider, with the rows of pins one or two positions farther apart.[1] These will not fit a (keyboard) PCB made for the proper hole spacing.
Shorts VBUS to Vcc
Some 5V clones have no 5V voltage regulator and diode or connect the regulator only to the RAW pin. This can be a problem for some split keyboards with a Pro Micro in each half of which only one is connected to the host: voltage on the VBUS input is usually used to determine which side should be master and which should be slave.
8 MHz crystal
Both 5V and 3.3V Sparkfun Pro Micros have a 16MHz clock crystal. The max clock for 3.3V is 8 MHz, and software intended to run on Pro Micros at 3.3V could set the prescaler to halve the input frequency — and then instead run at 4 MHz.

Developer information


  1. 40 Percent Club—Another black Pro Micro that's not the right size.. Dated 2018-08-08. Retrieved 2019-09-03