Timed blink is a version of well known Arduino blink example that is shipped with the standard IDE, but is redesigned to use the Abstraction and timer library. Example circuit for the code is exactly the same a blink, and if you use the inbuilt LED pin (which it does by default) then there’s no need to build any circuit whatsoever. Instead of using delay() calls to set the duration of the led flash, it uses the task management library to schedule a task.
IoAbstraction has full support for interrupts on most devices, meaning we can connect a Rotary Encoder to an Arduino using a standard PCF8574 IO expander chip. In order to do this we need the PCF8574 /INT line to be connected to an Arduino pin that supports interrupts (such as pins 2 or 3). Further, you can also have switches handle push button input without polling, by initialising for interrupt, especially useful with IO exapnders.
Matrix keyboards are arranged such that the keys are in a matrix of rows and columns. This means that instead of needing a spare input for each key, one INPUT for each column and one OUTPUT for each row is all that’s needed. In order to use the keyboard, we create a class of type MatrixKeyboardManager and configure it with an IoAbstractionRef, a KeyboardLayout that describes the keyboard attached (there are some standard ones already defined) and a listener that will be informed of changes.
Have you ever wanted to treat button presses in Arduino similar to other languages, where you get an event callback when the switch is pressed? Look no further, the IO abstraction library can do that with very little fuss. In fact it can also do the same for rotary encoders as well, treating them similar to how scroll bars work in desktop applications. To start we need to get the IoAbstraction library and open the buttonRotartyEncoder example.
Recently, I have made a fork of Arduino LiquidCrystal (HD44780 display driver library) that allows the library to work with the IO abstraction library, meaning you can configure a display to use Arduino pins, an i2c 8574 IO expander or shift registers by simply changing one line of code in your sketch. There are two additional examples provided with this version that show how to use the fork with both a shift register and an 8574 i2c IO expander.
Here we demonstrate the IO Abstraction library on an Arduino with a PCF8574 i2c 8-bit IO expander chip. We use the device in order to receive input from a switch and light an LED. It’s about the most basic example possible that has both input and output. To use this example, first download the IoAbstraction library. Devices such as the PCF8574 provide an easy way to expand both input and output capabilities using a single chip, and because it’s on i2c, needs only two pins from the Arduino (SDA and SCL).
Using SwitchInput for buttons and rotary encoders SwitchInput is a button and rotary encoder management library that treats button presses and encoder adjustments as events, similar to web and UI applications. Supporting as many switches and rotary encoders as you need, in an event driven way, working along with TaskManagerIO to keep your code clean. Key points: Buttons using either pull down or pull up logic connected directly or via any supported IO expander De-bouncing of events on all buttons and encoders to significantly reduce duplicate callbacks.
Troubleshooting IO issues using LoggingIoAbstraction Within the MockIoAbstraction.h header there is an implementation of BasicIoAbstraction that delegates through a logging layer. If you are having difficulty determining what your code is sending and receiving, this could be useful. Unit testing support within the library This library itself is quite well tested using AUnit, and further it makes unit testing your code easier. There is a MockIoAbstraction that provides very easy support for mocking out an IoAbstraction.
In this tutorial and accompanying youtube video (left), I discuss how Arduino inputs and outputs work. Arduino 8 bit boards are mainly based on Atmel AVR chips, in fact the Mega is named after the chip number AVR-Mega-2560. Outputs on the AVR chips are much more versatile than they first look, and the video covers this in detail. If you are using an Arduino pro or other 3V3 based Arduino, replace the 5V mentioned here with 3V3.
When we press a button that’s connected to an Arduino input, it is likely that the button will momentarily “flicker” between the on and off state. This gives false readings for a short period of time after the button is pressed. Problems caused by this can range from the mild annoyance of a slight flicker, to doing something more than once that should have only happened once. Therefore we need a way to ignore these false readings; ensuring we only consider the button pressed or released when we know for sure that it is “stable”.