A GPIO Python module, that works on many platforms.
The anyio package aims to mimic the basic functionality of the RPi.GPIO Python module that is used on the Raspberry Pi computer. 'Mimic' is used in the loosest sense of the word, because all it does is to implement 5 functions of the same name as the RPi.GPIO module. This allows you to write simple GPIO programs in Python, that work on Raspberry Pi, PC, Mac and Linux computers.
This package consists of two parts - a Python module that runs on a PC, Mac or Linux machine (well, anything that can run Python and pyserial), and some firmware that is programmed into an Arduino board. At the moment we only support an Arduino Pro Micro from SparkFun, but there's nothing really stopping it working on any Arduino. The two are linked together by a serial port controlled by the pyserial library. Calls to the anyio.GPIO methods on the host computer will cause reads or writes to the GPIO pins on the arduino platform.
In this way, it is possible to write a hardware control program on any platform, that can easily be ported between different platforms (including the Raspberry Pi). Just change the "import RPi.GPIO as GPIO" to "import anyio.GPIO as GPIO" and change your pin numbers, and you'll be working in no time!
The serial link between the two parts runs at 115200bps, and each command is only a few characters, so the system performs reasonably well unless you are repeatedly polling or changing lots of GPIO's at the same time.
USING A PRE-PROGRAMMED PRO-MICRO
For your convenience, you can buy an Arduino Pro Micro 3.3V 8MHz device with pre-soldered pin headers and pre-programmed anyio firmware from here:
http://skpang.co.uk/catalog/pro-micro-33v8mhz-with-headers-and-anyio-firmware-p-1327.html
All you need to do is plug it in, download this module by choosing the "Download as Zip" button, unzip the file and run the test programs, and you'll be working in no time!
PROGRAMMING THE PRO MICRO YOURSELF
If you are already familiar with Arduino programming and soldering, you might like to buy the raw components yourself and solder some headers on and program it yourself.
You can buy the bare unprogrammed Sparkfun ProMicro from here: https://www.sparkfun.com/products/12587
You can learn how to program the firmware here:
https://learn.sparkfun.com/tutorials/pro-micro--fio-v3-hookup-guide/introduction
The firmware that I use is in the following folder: anyio/arduino/firmware/gpio/gpio.ino
TESTING THE PRO MICRO
At the moment, this has only been tested with Python 2.7 - there are know issues we are looking at with some slightly earlier versions of 2.6 (to do with reading the version number of Python), and some known issues with all versions of Python 3 that we are looking at (to do with the way sub packages are imported). Our specific need was for a GPIO attachment for PC/Mac/Linux that worked with Python 2.7, but I will investigate and fix these issues later in 2014.
On Mac, you should just be able to plug the device in once it is programmed, and it hould appear as a serial port. When it pops up a box saying that a keyboard has been found, just close that box by pressing the red X button in the corner.
On windows, you have to install the ProMicro.inf using the instructions in the SparkFun hookup guide above. Note that this is a bit complex on Windows 8.1 due to the new "Driver enforcement mode" of windows, but the hookup guide on the sparkfun site does work if you follow it very carefully.
On linux (I've only tested on Ubunto 12.04LTS), plug it in and it should detect the device the first time you run one of your programs.
Once the device has it's firmware installed and it is plugged in, you are ready to run the test programs. Wire up a LED to pin 15, then run:
python testLED.py
The first time this runs, it will work out the serial port number. It will prompt you to remove the device and press ENTER (at which point it scans your system for serial ports), and then it will prompt you to insert the device and press ENTER (at which point it will re-scan to detect the newly inserted port). We have found this to be the most reliable method on all platforms for detecting a new serial port, compared to opening and testing each port (which can sometimes cause devices to lock up).
You will be shown the name of your serial port, and asked if you want to remember it - always choose Y so that your program will run correctly the next time you run it. It creates a small file called 'portscan.cache' which remembers the serial port number, you can delete this file if your serial port number changes for any reason and you want it to re-scan your system.
Your LED should now be flashing.
Once you have tried that, wire a button up to pin 4 and run:
python testButton.py
If you are getting excited at this point, wire up a 7-segment display to pins 7=a, 6=b, 14=c, 16=d, 10=e, 8=f, 9=g, 15=dp
If your display is Common Anode, edit testSeg7.py and set ON=True If your display is Common Cathode, edit testSeg7.py and set ON=False
Now run this to count through the numbers 0 to 9 on the display:
python testSeg7.py
USE OF PYSERIAL
This module uses pyserial to communicate with the Arduino Pro Micro.
anyio modifies the Python PACKAGEPATH for you when it runs, to make sure that it uses this embedded pyserial rather than one that might or might not be installed on your system. This means that if you don't have pyserial installed on your system, you should still be able to just run this out of the box and it should work.
If you already have pyserial installed and want to use your installed version for any reason, you can change the anyio/arduino/GPIO.py USE_EMBEDDED_PYSERIAL = False
FUTURE WORK
This package contains a console based (text mode) simulator that can be used to test your programs on before you connect to real hardware, and this supports both inputs and outputs. This console package works, but is not completely documented yet. You can try it with this: import anyio.console.GPIO as GPIO
The GPIO interface itself could be anything, not just an Arduino. There is a very simple protocol between the python module and the target GPIO hardware, that is written in a way to allow future extension to support other hardware peripherals such as I2C, SPI, UART, PWM, Analog, OneWire and other protocols and features aimed at near real time control and sensing.
There are placeholders in the design for a tkinter GUI simulator that I am planning to write soon, and also a network aware version, that allows GPIO controls to be sent remotely over a network connection to a GPIO server running on any arbitrary host computer (e.g. a Raspberry Pi).
NOTES ABOUT COPYRIGHTED MATERIAL
The source code in the anyio package is (c) 2014 David Whale.
There is an embedded version of pyserial inside the anyio package, and this is provided in it's entirely complete form, with it's original licence, which allows for it to be embedded inside other packages with out any special install.
There is an embedded version of the ProMicro.inf file, which came from the SparkFun github repository. It is included here for convenience, but the latest copy can always be retrieved from here:
https://github.com/sparkfun/SF32u4_boards/blob/master/driver/ProMicro.inf
David Whale June 2014