Thursday, January 27, 2011

Wise Clock 2 now with redesigned Duino644

Update Apr 15/2011 - Added schematic.

A new revision (2.1) of Duino644 is now available. The redesigned board features:
  • real time clock could be either DS3231 (extremely accurate RTC from Maxim) or the "old" DS1307;
  • the resistor-based voltage dividers for SD card have been replaced by 74AHC125 buffer chip;
  • small prototyping area, for adding extra functionality (e.g. automatic dimming with photo-resistor, FM radio etc);
  • power-indicator blue LED is now through hole (replaces the SMD).

Still in place are:
  • ATmega644P (DIP package) with 40-pin socket;
  • SD card socket;
  • infrared receiver;
  • piezoelectric buzzer;
  • 3 push buttons;
  • reset button;
  • two 2x8-pin connectors for direct plug-in with the 2416 LED display from Sure Electronics;
  • miniB USB as power connector;
  • ISCP 6-pin header;
  • 6-pin FTDI header;
  • four 8-pin headers for expansion boards ("shields").

The photo below shows the assembled board.

But don't get too excited: there are also 2 "minor" (easy to fix, fortunately) glitches:
  1. the FTDI header is too close to the display connector, so that the board cannot be inserted completely into the display, unless a piece of plastic from the display's connector is chopped off, as shown below.
  2. pin 3 of DS3231 (INT/SQW) is connected directly to D2 (pin 3) of ATmega644P, as is the output of the IR receiver. Basically, the IR receiver and DS3231 INT/SQW share the same interrupt. I initially thought of having a switch (2-pin header shunt) to connect INT/SQW to D2, but I got carried away and forgot to add it. There are 2 fixes for this: either software (modify the ISR) or just cut off the trace (and keep the software unmodified).

If you buy the complete Wise Clock 2 kit, I will cut both the display connector and the trace for you.
Otherwise, the Duino644 kit will have the unaltered board.

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