How to Connect Multiple Arduino Microcontrollers with I2C
Use I2c to connect several Arduinos together to combine their power. I2C stands for the Inter Integrated Circuits and is one of the best Multi Master Serial Computer Bus technologies used in different systems to connect the peripherals of low speed data transmission. The technology was invented by Philips for TVs but is used in all sorts of applications including our Wiimote and Arduino tutorial.
The I2C circuits follow a standard operational procedure where only two bi-directional lines, a serial clock, and a serial data systems are used.  There are recently improved versions of I2Cs available on the market which can hold a higher number of nodes and can perform faster than the rest.
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You can use I2C then you will be able to connect more than one Arduino to a robot or other application and you can easily establish a network of sensors. By using these circuits you will have more controller pins at your disposal which will allow you to add more devices. You do have other options such as an expander or Arduino Mega, but I2C because is significantly cheaper.
How To Set Up Your I2C
Here are the basic requirements for setting the I2C protocol with the Arduino:
- More than two Arduinos
- The latest version of the Arduino IDE
- Few pieces of hook up wire
- 1.5 to 2K Pull-up resistors
- You need to install the Arduino wire library (new versions have it built in)
If you are working with two Arduinos, then one must be the master and the other must act as the slave. To ensure a successful project, you need to make sure that you are using a minimum 1K pull-up resistor on every single line which will pull it to 5 Volts.
If you are interested in learning more about the I2C and the Arduino, here are a few great resources:
August 13th, 2009
Hello!
I’ve done some time in practice with the Arduino I2Cbus based on the Philips device PCF8574P, the truth is that I had no idea how complicated that would be, in principle I am trying to make a 4×3 numeric keypad, as is the example shown in this link:
http://www.arduino.cc/playground/Main/I2CPortExpanderAndKeypads
I can not get back the number of the button pressed.
I can help, what should I do to show me the number for the button pressed.
Thanks for your reply.
April 28th, 2011
I came here for learning to connect multiple Arduino cards together, but you just were talking about TWO !!!
April 29th, 2011
@Shahab – You can expand the number of Arduinos to as many as you’d like using this method.