ATtiny816 breakout with SeeSaw - StemmaQt / Qwiic
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ATtiny816 breakout with SeeSaw - StemmaQt / Qwiic

Breakout ATtiny816

  • Multi-purpose GPIO expander (I/O, ADC, PWM, NeoPixel)
  • Firmware SeeSaw
  • Interface: I2C

€6.70 (tax incl.) €5.54 (tax excl.)
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SeeSaw ATtiny816 : Three-in-one solution to add features to a project with limited I/O

This breakout board offers the following features:

  • The ATtiny816 is a tiny AVR microcontroler of next generation. It is mounted on a breakout board with just enough hardware to get it running.
  • Pre-programmed with the Adafruit seesaw firmware. Seesaw is a near universal firmware which allows you to add and extend hardware support via I2C bus (it is great to be used from microcontroller or microcomputer). The seesaw firmware allows to define GPIO, ADCs, PWM, NeoPixel pins over I2C all running on a unique component).
  • The StemmaQt/Qwiic connector is a JSTSH4 connector shipping power and I2C lines. It allows to quickly connect this board on StemmaQt or Qwiic capable board or to use a JSTSH4 adapter cable to connect it to any other microcontroler.

Adafruit did primilarly designed this board for internal use. It come to be a nice ATtiny816 development board and nicely support SeeSaw firmware like the ATSAMD09 SeeSaw does. With the 2021-2022 silicon shortage, the SAMD09 designs have been adapted to the ATTiny8xx series.

Each breakout comes with the assembled and tested board, as well as some header strips. Each PCB is fairly minimal and contains:

  • ATtiny816 8-bit microcontroller
            8KB flash, 512 bytes of RAM, 128 bytes of EEPROM
            Internal oscillator can run up to 20MHz
            Internal hardware multiplier
            Can run from 2V to 5V power/logic (check the datasheet for max speed at desired power)
  • 3.3V regulator - by default we run at the Vin voltage, which can be 5V, but there's a solder jumper on the bottom if you'd like to select 3V logic.
  • Indicator LEDs: Green for power, Red as activity LED
  • StemmaQt/Qwiic connector: connected to pins 8 and 9 with 10K pullup resistors.

This board comes pre-programmed with seesaw peripheral code that will let it act as an "I2C to something" converter, basically a little I2C-controlled friend to do all the timing-sensitive things many microcontrollers and microcomputers are not good at.

Using the ATtiny816 with seesaw firmware gives you:

  • 12x GPIO with selectable pullup resistors : 0-5, 6, 8, 11, 14, 15, 16
  • 9x ADC inputs : pins 0, 1, 2, 3, 4, 5, 14, 15, 16 -10bits resolution (0-1024)
  • 5x PWM outputs : pins 0, 1, 7, 11, 16 - 8bits resolution (0-255)
  • 1x NeoPixel output (up to 60 pixels)
  • 1x EEPROM with 127 bytes of NVM memory. Non Volatile Memory (NVM) are handy to store small access tokens, MAC addresses, etc.
    Note: the last byte of EEPROM is used for I2C address selection.
  • 1x Interrupt output : pin 6, can be triggered by any accessories
  • 2x I2C address selection pins : pins 12 and 13
  • 1x activity LED on pin 10, tied active low

Important notice

The SeeSaw product is an autonomous breakout board. As such the boards do not come with a bootloader. If you want to do development on seesaw (e.g. changing the configuration) you need a separate UPDI programming setup! The firmware we put on is available as this example sketch, compiled using the megaTinyCore. Adafruit does not provide any support for custom builds of seesaw!

The chip can be reprogrammed or reconfigured! You will need: (1) to use the SpenceKonde's megaTinyCore to brings Arduino peripheral support to this series of chips, (2) to program the chip with 'UPDI' programmer (can be made with USB-to-Serial cable and a single 4.7K or 10K resistor).


For each order, you will receive the Breakout ATtiny816 assembled and tested. An pinHeader row is included with the breakout if you need to use it on breadboard. The ATtiny816 AVR is preloaded with the SeeSaw firmware.


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