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.

Basic Usage

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.

Using Outputs

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

Using Relays

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

Using Classes

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

Using Inputs

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

Using Buttons

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

Advanced Usage

Reading Output

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

Stateless Relay class

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

Examples

For more examples, check out the examples directory.

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

Example Projects

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

Additional Resources

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

Installation

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

Contributing

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