arduinoattinyi2c
I am trying to create a smart alarm system for my house. I want to have one arduino as the master and several other AtTiny's as slaves to collect data as temperature, moisture, gas concentration, opened doors etc.
How do I connect multiple wired AtTiny's to a master Arduino? Which is the most clever way to communicate between them ? I have read that AtTiny's do not support spi or i2c but you can "hack" it somehow.
EDIT: the distance between the master and the slave can be 1 to 10 meters.
wire capacitance is what you are fighting - you can only go as fast as you pullup resistors can charge the parasitic capacitance of the wires - in the real world you make a good guess and then once you start working with the circuits drop a 'scope on on the data line - if you see a bunch of nice square waves you're good to go. On the other hand if you see a bunch of shark fins some of which don't make it all the way high before the clock edge you're either going too fast or need a smaller pullup
You could use an SPI to IIC bridge like this device.
Best Answer
If you happen to use those ATtiny that do not have hardware support of SPI or I2C, you can likely implement that in software, assuming you wont have any CPU-heavy processing running on the ATtiny (which is typically the case for mere sensor reading). That said, except for the 6-pins ones, most ATtiny's do have hardware support for both I2C and SPI (see product selector).
Choosing between I2C and SPI, I would go for the former given the multiple slave setup and the limited number of pins of the ATtiny (2 pins needed for I2C and 4 for SPI).