mxUnifiedIO

mxUnifiedIO base library for Arduino. Use device specific drivers with I/O expanders using a unified API.

mxUnifiedIO is a set of libraries for Arduino (IDE version 1.6 and up) that facilitate easy programming of multiple devices on I/O expanders or shift registers.

Currently the following expanders are supported:

• PCF8574 and PCF8575 I2C I/O expanders: https://github.com/maxint-rd/mxUnifiedPCF8574
• 74HC595 shift registers: https://github.com/maxint-rd/mxUnified74HC595

Currently the following device specific libraries are supported:

• Adafruit PCD8544 Nokia 5110 LCD: https://github.com/maxint-rd/mxUnifiedPCD8544_Nokia_5110_LCD
• e.dentifier2 LCD panel: https://github.com/maxint-rd/mxUnifiedLcdEdentifier2 (uses Adafruit GFX)
• SN76489 complex sound generator: https://github.com/maxint-rd/mxUnifiedSN76489
• HPDL1414 bubble LED display module: https://github.com/maxint-rd/mxUnifiedHPDL1414

Watch the YouTube videos Made: More pins for Arduino and ESP8266 and Made: Using a salvaged LCD to see it all in action. Read the device or I/O expander specific documentation and the documentation below for more information on how to use this library. This picture illustrates the main features of mxUnifiedIO:

MCU pin abstraction

The mxUnifiedIO base class provides the basic functionality of the specific expander libraries. It also provides abstraction of MCU pins, allowing uniform examples for different MCUs and pin-numbering independant use by device specific libraries. Note: the current version supports digitalWrite(), digitalRead() and pinMode(). Currently shiftOut() and PWM using analogWrite() is not implemented.

Using SPI shift register

The (shared) SPI bus requires three data-lines to connect one or more shift registers (SS, MOSI and SCK). On the Arduino UNO, Nano and Pro Mini, the pins for (fast) hardware SPI are D10, D12 and D13. On the ESP8266 the default SPI pins are GPIO15, GPIO13 and GPIO14. When using (slower) software SPI others can be selected too. See https://github.com/maxint-rd/mxUnified74HC595 for more info.

Using I2C I/O expander

The (shared) I2C bus only requires two data-lines (SDA and SCL). On the Arduino UNO, Nano and Pro Mini, these can be found on pins A4 and A5. On the ESP8266 the default pins are GPIO4 and GPIO5, but others can be selected too. See https://github.com/maxint-rd/mxUnifiedPCF8574 for more info.

Code examples

Each library comes with well commented and easy to read examples. It's easiest to start with the Blink examples. Typically you first include the required header files:

#include <mxUnifiedPCF8574.h>     // implies inclusion of <mxUnifiedIO.h>
#include <mxUnifiedPCD8544.h>

Then you can instantiate the required library objects:

mxUnifiedPCF8574 unio = mxUnifiedPCF8574(0x27, 2, 0);                // on ESP8266 you can other pins
mxUnifiedPCD8544 display = mxUnifiedPCD8544(&unio, 7, 6, 5, 4, 2);   // best pins for the LCD expander

In your setup() function you call the required begin() methods:

void setup()
{
  unio.begin();     // initialize the I2C connection with default I2C speed. 
  display.begin();  // regular begin() using default settings

  // show some text
  display.setContrast(50);
  display.clearDisplay();   // clears the screen and buffer
  display.println("Hello");
  display.display();
}

In your loop() you can do what you want, such as toggle a pin:

void loop()
{
  display.invertDisplay(true);
  unio.digitalWrite(0, HIGH);
  delay(1000); 
  display.invertDisplay(false);
  unio.digitalWrite(0, LOW);
  delay(1000); 
}

Adding device specific libraries

To make a library that uses mxUnifiedIO from an existing library is relatively easy. Take a look at the Nokia 5510 library which is derived from the Adafruit GFX library: https://github.com/maxint-rd/mxUnifiedPCD8544_Nokia_5110_LCD For many libraries replacing the digitalWrite() call is sufficient. For end-users it can be handy to encapsulate the library in a class. Per convention the pin definition is done in the contstructor, whereas the begin() method can be used to set specific initialisation parameters. The first parameter of the constructor should be a reference to the mxUnifiedIO expander object. The other parameters define the required (expanded) pins. (See example code above).

BTW: if you have implemented your own device library, please let me know, so I can mention it in the documentation.

Features & limitations

• The current version of this library supports ESP8266 and Atmel ATmega328 and ATmega168 MCUs. Support for ATtiny85 was just added to the base library (but not yet for all other libraries). Other Atmel processors may work as well, but they've not been tested yet. For some MCUs the libraries will require modification. Please let me know if you've successfully used this library with other MCUs.
• Currently the base mxUnifiedIO library provides abstration of digitalWrite(), digitalRead() and pinMode(). Other features such as pin interrupts, PWM and shiftOut() are not supported. The child libraries for the I2C I/O expander and for the shift register do support shiftOut(), but currently without the bitOrder parameter (MSBFIRST/LSBFIRST).

Disclaimer

• All code on this GitHub account, including this library is provided to you on an as-is basis without guarantees and with all liability dismissed. It may be used at your own risk. Unfortunately I have no means to provide support.