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You can try this open source version here https://github.com/zeevy/grblcontroller
i don't have a schematic for this, but this is pretty easy to connect.http://playground.arduino.cc/Main/MAX72XXHardware
Grbl Controller for Android...View Instructable »
Button are connected to analog pins (A0 - A3) of arduino with common ground.No external resistors are required.You can use push to on micro switches
RTC is connected to arduino via I2C lines.A4 on arduino is connected to the SDA pin of RTCa5 on arduino is connected to the SCL pin of RTC
Choose a good quality LEDs. I had a bad experience with cheep LED imported from china through ebay. They stopped working after few months.As you can see it is very hard to replace them from the display board
Unfortunately i don't have the circuit diagram for this, for wiring from arduino to display board you can refer the arduino sketch file. these may be helpfulhttp://playground.arduino.cc/Main/MAX72XXHardware
yes, as the digit size is over 2 inches it is easy to read from long distance.
Arduino MAX7219 Real Time C...View Instructable »