• RaspberryPiIOLibrary

Raspberry Pi I/O Library

I recently found an interesting measuring project with the Raspberry Pi from Tom Herbison, a HF Network Analyzer, see RaspberryPiWobbulator.

• In the process of building this project, I learned something about Input/Output programming with the Raspberry Pi, especially:

• GPIO
• I2C bus

I have looked at the following I/O libraries, with the main focus on Python programming:

• RPi_Low-level_peripherals

  • Python RPi.GPIO

  • raspberry-gpio-python

• Quick2Wire

• WiringPi

• i2c-tools, in the Debian repository, see also at software

Following I will give short references to the above mentioned Libraries, and some hardware references. All information are about the Raspberry Pi model B, revision 2.

RPi.GPIO

• Benefits
  • RPi.GPIO comes already with the operating system (Debian Wheezy)
  • high speed
• Drawbacks
  • Needs root rights
  • No bus support, I2C, SPI, 1-wire

Quick2Wire

From this company you can get an universal I/O board and good libraries, see at Links

• quick2wire-gpio-admin
  • Benefit: do not need root rights
  • Drawback: 10 times slower than RPi.GPIO
• quick2wire-python-api for GPIO and I2C

WiringPi

Wiring is used for the Arduino computer modules, in order to simplify the Input/Output programming. It is also ported to the Raspberry Pi.

• Drawbacks: needs root rights, special pin numbering
• Benefit: similar to the Arduino system

• very good Pin reference

Raspberry Pi, hardware

Unfortunately there are 4 different naming systems for the I/O pins, and 2 hardware revisions (Rv1, Rv2). You always struggle which is which.

• header pins, numbers P1: 1 to 26
• Names, e.g. GPIO0, SDA
• BMC GPIO numbers

• WiringPi pin, numbers P1: 0 to 16, P5: 17 to 20

• Example pin naming from top to bottom: 8 = Rv1:0, Rv2:2 = (I2C)SDA = 3

The I/O port from the Raspberry Pi can be fed via 26 pin flat cable to a half size proto board, price about 6.50 EUR, see Links. This is for me the cheapest I/O extension for doing prototyping.

For the pin naming please see at Links.

Raspberry Pi, software

For the I2C/TWI interface bus you need a driver library, see Links, and must be enabled in Linux. For installation do:

# install documentation tool
$ sudo apt-get install pandoc

$ make check-install

# tools to install
$ sudo apt-get install python-pip
$ sudo apt-get install python-virtualenv

# install GPIO library
$ cd quick2wire-gpio-admin-master
$ make
$ sudo make install
$ man gpio-admin
# logout and login again, to activate the group assignment

# check for function (24(BCM) = 18(pi_header_1) = 5(pins) = DATA on DDS-Generator)
$ gpio-admin export 24
$ cat /sys/devices/virtual/gpio/gpio24/value
0
$ echo out > /sys/devices/virtual/gpio/gpio24/direction
$ echo 1 > /sys/devices/virtual/gpio/gpio24/value
$ cat /sys/devices/virtual/gpio/gpio24/value
1
# shut off pin
$ gpio-admin unexport 24

# install
$ cd quick2wire-python-api-master/
$ sudo adduser $USER i2c
# logout and login again, to activate the group assignment
or reboot later

# install i2cdetect
$ sudo apt-get install i2c-tools

# Enable I2C bus software:
# edit file /etc/modprobe.d/raspi-blacklist.conf
  # Quick2wire software library needs it 2013-12-09 RR
  #blacklist spi-bcm2708
  #blacklist i2c-bcm2708

# edit file /etc/modules
# add line at the end:
  i2c-dev

$ sudo reboot

# check for i2c device descriptor
$ ls /dev/i2*
crw-rw---T 1 root i2c  89, 0 Dez  9 18:14 /dev/i2c-0
crw-rw---T 1 root i2c  89, 1 Dez  9 18:14 /dev/i2c-1

# check for modules
$ lsmod
Module                  Size  Used by
i2c_dev                 5620  0
snd_bcm2835            15846  0
snd_pcm                77560  1 snd_bcm2835
snd_seq                53329  0
snd_timer              19998  2 snd_pcm,snd_seq
snd_seq_device          6438  1 snd_seq
snd                    58447  5 snd_bcm2835,snd_timer,snd_pcm,snd_seq,snd_seq_device
snd_page_alloc          5145  1 snd_pcm
spidev                  5224  0
leds_gpio               2235  0
led_class               3562  1 leds_gpio
spi_bcm2708             4510  0
i2c_bcm2708             3759  0


$ sudo i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- 05 -- -- -- -- -- -- -- -- -- --
....

# link Quick2Wire-API (i2c) library to Python
# edit /home/pi/.profile
# add
  # for I2C use
  export QUICK2WIRE_API_HOME=/home/pi/Install/quick2wire-python-api-master
  export PYTHONPATH=$PYTHONPATH:$QUICK2WIRE_API_HOME
# logout and login again, to activate the environment

In order to start the program wobbulator.py from the command line the first line must be a shebang line, see also Links:

• #!/usr/bin/env python3

Links

• Wikipedia Beschreibung

• Mikrocontroller.net, Deutsch Raspberry Pi Erklärungen

• wikipedia, I2C

• I2C addressing

• Serial Resistances and Debugging

• Bus Pirate 3, I2C guide, as master and sniffer

• Exploring a digital I2C/SPI accelerometer (MMA7456L) with Bus Pirate

• Raspberry Pi and Arduino linked via I2C library

• quick2wire-python-api

• quick2wire-gpio-admin

• physical-python-part-1, I2C/TWI

• Adafruit Half-size Perma-Proto Raspberry Pi Breadboard PCB Kit, $6

• Python shebang line

• Raspberry Pi GPIO header pin numbers

• accessing-the-gpio-of-a-raspberry-pi-without-sudo

• WiringPi2-Python

• very good Pin reference

• Enable Raspberry Pi I2C bus

List of pages in this category:

-- RudolfReuter 2013-12-19 09:29:08

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