D21G features



Real Time Clock - RTC

Industruinos with the D21G topboard have a built-in RTC (MCP79402 with I2C 0x57 and 0x6F) that can be used with this library

A simple example that displays the date and time on the LCD can be found here.


The D21G does not have any built-in EEPROM as the usual Arduino chips have, but the board includes external EEPROM over I2C. Addresses are 0x50, 0x51, 0x52, 0x53.

Each of the 4 I2C addresses have 255 bytes available; in total 1kByte.

This EEPROM can be used with this library, or you can also use the Wire library directly to read/write bytes.

Check out this example sketch that uses the above library to write/read byte, long, and float types (including the conversions), output on the left.

WDT - Watchdog Timer

The Adafruit SleepyDog library works on the D21G as in this example.

It requires the installation of the ASF core library too.

The above example activates a watchdog timer of 4 seconds, and goes through 10 loops that include a watchdog.reset() which tells the WDT that all is fine. Then it starts a delay() that is longer than the WDT period, so after 4 seconds the unit resets and starts the sketch again. 


This library also has a sleep function to reduce power consumption. Have a look at the library example 'sleep.ino' and use the function (for 5 seconds sleep)

  int sleepMS = Watchdog.sleep(5000);

My test on a PROTO D21G show (12V on Vin):

  • awake, full backlight: 8mA (may be higher on more recent batches)
  • awake, no backlight: 5-7mA
  • sleeping, no backlight: 2mA
When the PROTO is powered by 5V (on 5V terminal), the results are:
  • awake, full backlight: 17mA (may be higher on more recent batches)
  • awake, no backlight: 13mA
  • sleeping, no backlight: 4mA

For an IND.I/O D21G the results are (12V, I/O channels not connected to anything):

  • awake, full backlight: 180mA
  • sleeping, no backlight: 175mA
So not much power is saved with the sleep mode, as the IND.I/O baseboard already draws 49mA in idle state, without the MCU/topboard connected.
Please note that upload seems to be disabled in sleep mode, so to activate the D21G's bootloader, it may be necessary to press the Reset button on the topboard twice.