Pinouts

The ItsyBitsy 32u4's come in two flavors - 5V and 3V.

The pinouts for these are very similar except for the power pins which have different voltages!

Which do you have?

 

Look in the middle of the board, you'll see either 32u4 3V 8MHz or 32u4 5V 16 MHz

Power Pins

Both ItsyBitsy 32u4's have BAT G USB on the top left, right next to the micro USB port

These pins are:

  • BAT - battery input for an alternative power source to USB.
    On the 5V itsy, this pin can be 5.5-16VDC
    On the 3V Itsy, we have a different regulator, so the voltage can only be from 3.5V to 6VDC
  • GND - Power/data ground
  • USB - This is the same pin as the MicroUSB connector's 5V USB power pin. This should be used as an output to get 5V power from the USB port. Say if you need to power a bunch of NeoPixels or servos.

You can always put any voltage you like into BAT and the circuitry will switch between BAT and USB dynamically for you. That means you can have a Batter backup that only gets enabled when USB is disconnected.

If you want to add rechargeable power, a LiPoly backpack can be soldered into these three pins that will let you have a battery that is automatically recharged whenever USB is plugged in, then switches to LiPoly when on the go:

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5V Power Pins

In addition to the three standard power pins, the 5V ItsyBitsy has a few more pins available for power sourcing:

  • 5V - this is the regulated output from the onboard regulator or the USB connection (if its powered!) You can draw 500mA when USB is connected, or up to 150mA when on battery.
  • 3V - this power pin is in the bottom right corner. It is a small 3V output from the on-chip regulator. It's very low current, we don't recommend drawing more than maybe 10 mA from this, but it can run small sensors!
  • EN - connected to the regulator enable, it will let you shut off power - when running on battery only. But at least you don't have to cut a trace or wire to  your battery. This pin does not affect power when using USB
  • G - these are all Ground pins

3V Power Pins

In addition to the three standard power pins, the 3V ItsyBitsy has a few more pins available for power sourcing:

  • 3V - this is the regulated output from the onboard regulator. You can draw 500mA whether powered by USB or battery.
  • Vhi - this is a special pin! It is a dual-Schottkey-diode connected output from BAT and USB. This means this will always have the higher-of-the-two voltages, but will always have power output. The voltage will about 5VDC when powered by USB, but can range from 3.5-6VDC when powered from battery. It's not regulated, but it is high-current, great for driving servos and NeoPixels.
  • EN - connected to the regulator enable, it will let you shut off power - when running on battery only. But at least you don't have to cut a trace or wire to  your battery. This pin does not affect power when using USB
  • G - these are all Ground pins

Logic pins

This is the general purpose I/O pin set for the microcontroller. All logic is 3.3V on the 3V Itsy, and 5V on the 5V Itsy. You can usually use 3V logic as an input to 5V, but the 3V Itsy pins should not be connected to 5V!

Along the right edge

  • #0 / RX - GPIO #0, also receive (input) pin for Serial1 and Interrupt #2
  • #1 / TX - GPIO #1, also transmit (output) pin for Serial1 and Interrupt #3
  • #2 / SDA - GPIO #2, also the I2C (Wire) data pin. There's no pull up on this pin by default so when using with I2C, you may need a 2.2K-10K pullup. Also Interrupt #1
  • #3 / SCL - GPIO #3, also the I2C (Wire) clock pin. There's no pull up on this pin by default so when using with I2C, you may need a 2.2K-10K pullup. Can also do PWM output and act as Interrupt #0.
  • #5 - GPIO #5, can also do PWM output. On the 3.3V ItsyBitsy this is a special OUTPUT-only pin, that is level-shifted up to Vhi voltage, so its perfect for driving NeoPixels that want a ~5V logic level input.
  • #7 - GPIO #7. Also hardware Interrupt #4
  • #9 - GPIO #9, also analog input A9 and can do PWM output.
  • #10 - GPIO #10, also analog input A10 and can do PWM output.
  • #11 - GPIO #11, can do PWM output.
  • #12 - GPIO #12, also analog input A11
  • #13 - GPIO #13, can do PWM output and is connected to the red LED next to the Reset button

Along the left edge

  • A0 thru A5 - These are each analog input as well as digital I/O pins.
  • SCK/MOSI/MISO - These are the hardware SPI pins, you can use them as everyday GPIO pins but recommend keeping them free as they are best used for hardware SPI connections for high speed. Also used to reprogram the chip with an AVR programmer if you need.

Along the short edge:

  • #4 - GPIO #4, also analog input A6
  • #6 - GPIO #6, can also do PWM output and analog input A7
  • #8 - GPIO #8, also analog input A8

Other Pins!

  • RST - this is the Reset pin, tie to ground to manually reset the AVR, as well as launch the bootloader manually
  • ARef - the analog reference pin. Normally the reference voltage is the same as the chip logic voltage (3.3V or 5V) but if you need an alternative analog reference, connect it to this pin and select the external AREF in your firmware. Don't set it higher than the logic level of the Itsy!
This guide was first published on Jan 03, 2018. It was last updated on Oct 19, 2018. This page (Pinouts) was last updated on Jun 09, 2018.