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Arduino I2C Port Expander

This is a library to turn any Arduino compatible microcontroller into the ultimate I2C port expander. Now with ATtiny support.

Features

Functions

  • Digital Write
  • Digital Read
  • Digital Read with internal pullup
  • Analog Read
  • Analog Write (PWM)

###Special Functions###

  • 4 wire resistive touchscreen controller

Why is this needed?

There are a lot of port expanders out there. I always have the same problem with them. They only do one thing. One can read or write digital inputs. Another can write pwm. Still anothher can read analog inputs. They do their own thing well but they can only do that one thing. Most microcontrollers have multiple capabilities, including the microcontroller on Arduino. It has all of these functions and much much more. This makes it the perfect cantidate for the ultimate port expander for any project.

Getting Started

With the Arduino IDE closed, download or clone this repository and place it in the libraries folder. Open up Arduino and go to File > Examples > Arduino I2C Port Expander > Slave I2C Port Expander. Upload this code to your microcontroller that you want to become a port expander.

Next, load the Master Controller Example from the same examples folder. Load this sketch on the board that you want to be the master.

Now, connect both the master and the slave together. They must share a ground. Hook up the I2C lines on both. It is best to use a 4.7k resistor to pull them both to 5v or vcc. Then just power them on, and the blink sketch should begin to run on the master and blink the LED on pin 13 on the slave.

Functions

When you initialize this library on the master, you have to give it a name. For the code examples, we will assume you named it "io".

  • io.digitalWrite(pin, HIGH | LOW); - Writes pin HIGH or LOW

  • io.digitalRead(pin); - Returns pin value as an int. 0 for low or 1 for high

  • io.digitalReadPullup(pin); - Same as digital read, but activates the internal pullup resistor first.

  • io.analogRead(pin); - Returns analog read value as int. Must call slaves digital pin number not its analog pin. So use 14 instead of A0.

  • io.analogWrite(pin, 0-255); - Writes pwm to pin. Must be a pwm capable pin.

Special Functions

###4 Wire Touchscreen###

The touchscreen code is based on Adafruit's Touch Screen Library. You do not need to install this library, as the required code in included in the slave example. Pins are defined in the example sketches. They can be changed to suite your needs. The pins function as normal inputs and outputs until you call touchscreenOn();.

  • touchscreenOn(); - Initializes the touchscreen function. Must be called before touchscreen can be used.
  • touchscreenReadX(); - Returns an int with value of x axis touch value.
  • touchscreenReadY(); - Returns an int with value of y axis touch value.
  • touchscreenReadZ(); - Returns an int with value of z axis touch value. (pressure)

Supported Microcontrollers

This library should support all microcontrollers that work with Arduino and can use the Wire library.

For ATtiny microcontrollers, you need to have the TinyWireS library. Currently, ATtiny microcontrollers only work as a port expander, not a master. It should be easy to port over, but I do not see the point.

The included ATtiny example has been tested with the ATtiny84 using 8mhz internal clock, but should work with all versions supported by TinyWireS.

For board support of the ATtiny microcontrollers, I recommend Damellis' ATtiny package.

Future Plans

  • Add Soft PWM to enable PWM on all pins
  • Add Character LCD support
  • Add Sevo Capability
  • Make Raspberry Pi library
  • Make it self aware and take over the human race (unlikely)