Arduino Yun - not enough i2c & interrupt pins?

Question

I'm trying to build a small personal weather station. The rain sensor, and wind speed sensor use interrupts. The barometric sensor uses i2c SDA and SCL.

Reading the Arduino Yun manual, it says there are 5 interrupt pins, but 2 of them are SCL/SDA (pins D2 and D3), and 2 of them are serial comms between Linio and the 32U4 (pins 0 and 1).

This leaves me with 1 interrupt pin left (pin 7).

Is there a work around to get my 2 digital sensors AND SDA SCL pins connected?

If I do use pins 0 and 1 (Linux serial), what do I risk? I will need to use the Bridge to relay information to the internet.

Answer 1

Any of the port B pins on the ATmega32u4 can interrupt on pin change. Unlike the external interrupts however, these pin change interrupts share the same interrupt vector. So in the interrupt routine you have to work out which one fired.

The port B pin change interrupt is not support by the Arduino core library so you have to download a third-party library. This one seems fairly recent:

https://code.google.com/p/arduino-pinchangeint/

Then you connect your two interrupt lines to spare Port B pins and monitor for pin changes.

Answer 2

OR the interrupt lines together so that you only need 1 external interrupt. Then when an interrupt is triggered, poll the devices until you find the one that triggered the interrupt. If the interrupt outputs are open-drain then you can wired-OR them together, otherwise you will need something like the 74LVC32 to OR the push-pull outputs together.