More External Interrupts

I like interrupt driven processing. No need to be looping around listening to input lines.

The current Arduino (Arduino Dueminalove and clones) only has two external interrupt lines:

From the Arduino documentation:

Each of the 14 digital pins on the Duemilanove can be used as an input or output, using pinMode(), digitalWrite(), and digitalRead() functions. They operate at 5 volts. Each pin can provide or receive a maximum of 40 mA and has an internal pull-up resistor (disconnected by default) of 20-50 kOhms. In addition, some pins have specialized functions:

• Serial: 0 (RX) and 1 (TX). Used to receive (RX) and transmit (TX) TTL serial data. These pins are connected to the corresponding pins of the FTDI USB-to-TTL Serial chip.
• External Interrupts: 2 and 3. These pins can be configured to trigger an interrupt on a low value, a rising or falling edge, or a change in value. See the attachInterrupt() function for details.
• PWM: 3, 5, 6, 9, 10, and 11. Provide 8-bit PWM output with the analogWrite() function.
• SPI: 10 (SS), 11 (MOSI), 12 (MISO), 13 (SCK). These pins support SPI communication, which, although provided by the underlying hardware, is not currently included in the Arduino language.
• LED: 13. There is a built-in LED connected to digital pin 13. When the pin is HIGH value, the LED is on, when the pin is LOW, it's off.

This will not be enough if we use interrupts for the rotary encoder and the IR Remote (more on IR remote later) and future enhancements.

Fortunately there is a new Arduino in the making: the ARDUINO MEGA. On paper, the new microcontroller, the ATMEL 1280 has at least 8 external interrupt lines. The specifications of the new board has not yet been released. So we don't know exactly how many external interrupt lines will be supported. Here is a photo of the new board: