Ruby Bindings for pfio.c

The pfio C Library is used to control the Pi-Face Digital Interface for Raspberry Pi. This gem uses the Ruby-FFI gem to bind the C functions to ruby.

The PiFace has 8 inputs and 8 outputs. Both the inputs and outputs are linked to connectors 1-8 respectfully.

Note: By default, the input and output pins will not be reset when first initialized. To find out more, see Piface Initialization.

Writing to outputs 1 to 8 with all turn on the LEDs. Write to outputs using Piface::LOW (or 0) for off/disable and Piface::HIGH (or 1) for on/enable.

Please note that the PiFace outputs are all open-collectors (meaning that they do not output any voltage). Please read the PiFace Manual for more information.

require 'piface'

# Enable output 4
Piface.write 4, 1

sleep 1 # wait one second

# Disable output 4
Piface.write 4, 0

Write to outputs 1 and 2 to control the relays (if jumpers JP5 and JP6 are enabled on the PiFace).

require 'piface'

# Turn on the first relay
Piface.write 1, 1

sleep 1 # wait one second

# Turn off first relay
Piface.write 1, 0

Sometimes it's nice to represent an output using a class. One common example is when you want to track the current state of the output. Also see the Stateless Relay Class

require 'piface'

# Relay class implementing toggle functionality
class Relay
  def initialize(relay_number)
    @relay_number = relay_number
    @state = 0
  end

  def turn_on
    Piface.write @relay_number, 1
    @state = 1
  end

  def turn_off
    Piface.write @relay_number, 0
    @state = 0
  end

  def toggle
    @state == 1 ? turn_off : turn_on
  end
end

relay1 = Relay.new(1)

# Turn the relay on and off 3 times
6.times do
  relay1.toggle
  sleep 1 # wait one second
end

The PiFace uses digital inputs. Reading the value with return either a 0 or 1. Since the PiFace uses pull-up resistors for inputs, by default they will read 1. This means to check for input (such as button presses), you must compare the read input value with 0 for on.

require 'piface'

# Read value from input 6 (without active input)
Piface.read 6
# => 1

# Read value from input 6 (with active input)
Piface.read 6
# => 0

The PiFace has 4 built-in buttons that correspond to inputs 1 to 4.

require 'piface'

# Listen for button 4 press
loop do
  # Check if the button has been pressed
  if (Piface.read(4) == Piface::LOW)
    puts "Button 4 pressed"
  end
  sleep 0.1 # sleep to be kind to the CPU
end

If you need to check whether or not an output is active, you can easily read an output state with the read_output method.

require 'piface'

# Read the current output of pin 8 (when off)
Piface.read_output 8
# => 0

# Read the current output of pin 2 (when on)
Piface.read_output 2
# => 1

If you have multiple scripts running, it can be hard to keep track of output states. By using a stateless class, you can implement a toggle method that reads the current state, instead of using a stored state. Keep in mind that by reading the state is it less effecient.

require 'piface'

class Relay
  def initialize(relay_number)
    @relay_number = relay_number
  end

  def turn_on
    Piface.write @relay_number, 1
  end

  def turn_off
    Piface.write @relay_number, 0
  end

  def state
    Piface.read_output(@relay_number)
  end

  def toggle
    new_state = state ^ 1
    Piface.write @relay_number, new_state
  end
end

relay2 = Relay.new(2)
relay2.toggle # toggle the light without using a stored state

For more examples, check out the examples directory.

• led
• pir sensor
• relay (same as stateless relay)
• toggle button

• Siriproxy Piface - "I used my RPi, PiFace IO board, along with SiriProry as a simple voice controlled garage door opener."

• The PiFace Digital PDF Manual
• pfio C Library
• WiriingPi Library

Enable RaspberryPi's SPI module (required on each reboot)

$ sudo modprobe spi_bcm2708
$ sudo chown `id -u`.`id -g` /dev/spidev0.*

Add this line to your application's Gemfile:

gem 'piface'

And then execute:

$ bundle

Or install it yourself as:

$ gem install piface

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Added some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request