We developed 28Pins to help people to learn how to design their own boards. The board is based on Arduino project and it's part of our online course called "Learn To Design Your Own Boards" at FEDEVEL Academy. On this website you will find all the project files such Schematic, PCB or Firmware. Feel free to use it in your own personal and commercial projects. Just follow the Attribution-ShareAlike 3.0 Unported licence. Have a fun! :)
We made couple of changes to the original Arduino schematic
Reset improvement
Both RESET pins ( 16U2 and 328P ) are now driven through an open drain buffer. This means: improved RESET quality and it adds an option to debug the microcontrollers through dWire.
3.3V and 5V Support
If you would like to connect 28Pins to a board with 3.3V pins, you can. We added an option to switch between 5V or 3.3V pin voltage. Simply, just change the JP4 jumper.
Use it as a Programmer
ATMEGA16U2 can now be used as an universal AVRISP MKII programmer. Once you change the firmware, you can use it to program the onboard ATMEGA328P or any other board.
Other
Micro USB (use any mobile phone or tablet charger to power the board), User Button added, DFU Disable jumper, dWire debugger (if correct firmware is used, 16U2 can work as an dWire debugger).
28Pins Board Specification
There are two microcontrollers placed on the board, ATMEGA328P and ATMEGA16U2.
1x ATMEGA328P
- FLASH: 32kB / EEPROM: 1kB / RAM: 2kB
- Clock: 16MHz (for +5V) / 10MHz (for +3.3V)
- Up to 20 input / output pins from which:
- 20x digital input/output
- 6x PWM output
- 6x Analog inputs (10bit AD)
- 1x Serial port, 1x SPI, 1x I2C
- 1x User LED
- 1x User Buton, 1x Reset Button
1x ATMEGA16U2
- FLASH: 16kB / EEPROM: 512B / RAM: 512B
- Clock: 16MHz (for +5V) / 8MHz (for +3.3V)
- 4x Digital input / output
- 2x User LED
- 1x USB
- 1x SPI
- 1x Serial port (shared with 328P)
- DFU programming support
- AVRISP MKII firmware available
And more ...
- ATMEGA328P can be programmed from ATMEGA16U2
- SPI programming support
- dWire debugging support
- On board +3.3V / 1.5A regulator
- Optional: Selection between +3V3 or +5V IO voltage
- Size: 2.7 x 2.1 inch (68.6 x 53.4 mm)
- Power input: micro USB or soldered wires
- Power voltage: +5V (from PC, tablet & mobile phone charger or an external power supply)
