AS UNO
A picture is worth a 1000 words they say:
Note the lack of a USB Serial chip, and LEDs.
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Pads for a crystal are provided. - It is intended for use with a 16MHz or 20MHz crystal. I strongly suggest that you use MCUdude's MiniCore boards package if using other than the default 16MHz of the Arduino IDE - JSON file is at https://mcudude.github.io/MiniCore/package_MCUdude_MiniCore_index.json To keep timing correct the Arduino IDE need to be informed of the crystal frequency that you are using. You can do this yourself by changin 1 line in "boards.txt".. OR.. the abovementioned boards package gives you drop down menus from the "Tools" menu. One of my boards.txt files has these lines:
# uno.build.f_cpu=16000000Luno.build.f_cpu=20000000Lyou can see where I commented out the existing 16MHz and replaced it with 20MHz.
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No USB Serial - The female header at the end of the board is to accept a CP2102 USB-UART module. This will allow you to upload sketches just like a regular UNO or Nano, but doesn't drain you battery once it is removed. It also provides regulated +5 and 3V3.
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No LEDs - There are pads to install a 3mm Power LED and 'L' LED to the right of the MCU. Giving you the choice to waste juice on pretty lights.
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5 Sel 3 - This is a legacy carry-over from the 8MHz board - It should disappear in a future revision. Should be jumpered or solder shorted from 5 to the 'Sel' pad. The ATmega328P chokes on 3V3 above ~12MHz. Conversely you could use 'Sel' as a Vin pin.
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0 .... 7 - these are Arduino pins D0 thru D7 as in
digitalWrite( 4, HIGH );they form the 'D' bus. Pins 0 and 1 correspond to Serial Tx and Rx respectively. -
Reg 3V3 - This is for a Regulator module - more on this at a future date. Middle pin may be used as a GND connection.
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LEDs - 2 sets of pads are provided for installing LEDs to the right of the MCU labelled Power and LED (the Arduino LED_BUILTIN on pin D13). They have higher value resistors in series to keep from blinding you as you marvel at the board during development.
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ICSP - 2x3 Header - this is the InCircuit Syste Programmer interface used to directly program the chip via an USBasp. They are available with 10 pin to 6 pin adapters. Pin 1 - indicated with a square pad on the bottom of the board is MISO - This bus is the SPI bus. If you upload a sketch with an USBasp you will lose the bootloader - your sketch will start immediately but you will not be able to upload via the USB Serial until you re-install a bootloader with the USBasp. The clock frequency (and other fuses) of the chip are set during the bootloader burn process. Be sure to select the Externa Oscillator before burning if using the MCUdude package... There is no external crystal.
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B0 .... B5 - these are Arduino pins D8 thru D13 as in
digitalWrite( 13, HIGH );they form the 'B' bus. Arduino pin numbers are shown on the bottom of the board. Pin 13 (B5) drives the on-board LED. (pins 14 and 15 are used by the crystal). -
A0 .. A3 - these are the Analog pins A0 thru A3 as in
analogRead( A2 );they form part of the 'C' bus. They may also be used as Digital I/Os. -
G +V CK SD - these are my OLED socket where you can plug in one of those 0.91" tiny I2C OLED displays. G = GND, +V = +5 VDC, CK is the I2C SCL pin which is also Analog A5, , SD is the I2C SDA pin which is also Analog A4, A4 and A5 are part of the 'C' bus.
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CP2102 Header - the female header at the end of the board has the following pinout: (from top to bottom)
Pin 1 = 3V3 input - not used on this board - Square pin on the bottom of the board indicates pin 1.
Pin 2 = DTR output - used by the IDE to reset the board to initiate uploading.
Pin 3 = RxD input - the board outputs serial data on this pin for input to the IDE Serial Monitor.
Pin 4 = TxD output - the board receives serial data on this pin from the IDE Serial Monitor or uploader.
Pin 5 = Gnd.
Pin 6 = Regulated +5 VDC.
