Welcome to PiFace Digital I/O’s documentation!¶

The pifacedigitalio Python module provides functions and classes for interacting with PiFace Digital.

Links:

Contents:

PiFace Digital¶

PiFace Digital has eight inputs, eight outputs, eight LED’s, two relays and four switches.

Outputs¶

The eight output pins are located at the top of the board (near the LEDs). The outputs are open collectors, they can be thought of as switches connecting to ground. This offers greater flexibility so that PiFace Digital can control devices that operate using different voltages. The ninth pin provides 5V for connecting circuits to.

LEDs¶

The LED’s are connected in parallel to each of the outputs. This means that when you set output pin 4 high, LED 4 illuminates.

>>> import pifacedigitalio
>>> pifacedigital = pifacedigitalio.PiFaceDigital()
>>> pifacedigital.output_pins[4].turn_on()  # this command does the same thing...
>>> pifacedigital.leds[4].turn_on()  # ...as this command

Relays¶

The two Relays are connected in parallel to output pins 0 and 1 respectively. When you set output pin 0 high, LED 0 illuminates and Relay 0 activates.

>>> import pifacedigitalio
>>> pifacedigital = pifacedigitalio.PiFaceDigital()
>>> pifacedigital.output_pins[0].turn_on()  # this command does the same thing...
>>> pifacedigital.leds[0].turn_on()  # ...as this command...
>>> pifacedigital.relays[0].turn_on()  # ...and this command...

When activated, the relay bridges the top and middle pins. When deactivated the bottom two are connected.

Relay activated:

[Top Pin   ]
[Common    ]
 Bottom Pin

Relay Deactivated:

 Top Pin
[Common    ]
[Bottom Pin]

Inputs¶

The eight input pins detect a connection to ground (provided as the ninth pin). The four switches are connected in parallel to the first four input pins. The inputs are pulled up to 5V. This can be turned off so that the inputs float.

>>> import pifacedigitalio
>>> pifacedigital = pifacedigitalio.PiFaceDigital()
>>>
>>> # without anything pressed
>>> pifacedigital.input_port.value
0
>>> pifacedigital.input_pins[0].value
0
>>> pifacedigital.switches[0].value
0
>>>
>>> # pressing the third switch
>>> pifacedigital.input_port.value
8
>>> bin(pifacedigital.input_port.value)
0b100
>>> pifacedigital.input_pins[2].value  # this command is the same as...
1
>>> pifacedigital.switches[2].value  # ...this command
1

Installation¶

Make sure you are using the lastest version of Raspbian:

$ sudo apt-get update
$ sudo apt-get upgrade

Install pifacedigitalio (for Python 3 and 2) with the following command:

$ sudo apt-get install python{,3}-pifacedigitalio

Test by running the blink.py program:

$ python3 /usr/share/doc/python3-pifacedigitalio/examples/blink.py

Emulator¶

Install python3-pifacedigital-emulator with the following command:

$ sudo apt-get install python3-pifacedigital-emulator

Start the emulator with:

$ pifacedigital-emulator

Note

You must be in an X11 session (startx).

Examples¶

Basic usage¶

>>> import pifacedigitalio

>>> pfd = pifacedigitalio.PiFaceDigital() # creates a PiFace Digtal object

>>> pfd.leds[1].turn_on()    # turn on/set high the second LED
>>> pfd.leds[1].set_high()   # turn on/set high the second LED
>>> pfd.leds[2].toggle()     # toggle third LED
>>> pfd.switches[3].value    # check the logical status of switch3
0
>>> pfd.relays[0].value = 1  # turn on/set high the first relay

>>> pfd.output_pins[6].value = 1
>>> pfd.output_pins[6].turn_off()

>>> pfd.input_pins[6].value
0

>>> pfd.output_port.all_off()
>>> pfd.output_port.value = 0xAA
>>> pfd.output_port.toggle()

>>> bin(pfd.input_port.value)  # fourth switch pressed (logical input port)
'0b1000'

>>> bin(pfd.gpiob.value)  # fourth switch pressed (physical input port)
'0b11110111'

>>> pfd.deinit_board()  # disables interrupts and closes the file

Here are some functions you might want to use if objects aren’t your thing:

>>> import pifacedigitalio as p
>>> p.init()
>>> p.digital_write(0, 1)    # writes pin0 high
>>> p.digital_write(5, 1, 2) # writes pin5 on board2 high
>>> p.digital_read(4)        # reads pin4 (on board0)
0
>>> p.digital_read(2, 3)     # reads pin2 (on board3)
1
>>> p.deinit()

Interrupts¶

Instead of polling for input we can use the InputEventListener to register actions that we wish to be called on certain input events.

>>> import pifacedigitalio
>>> def toggle_led0(event):
...     event.chip.leds[0].toggle()
...
>>> pifacedigital = pifacedigitalio.PiFaceDigital()
>>> listener = pifacedigitalio.InputEventListener(chip=pifacedigital)
>>> listener.register(0, pifacedigitalio.IODIR_FALLING_EDGE, toggle_led0)
>>> listener.activate()

When input 0 is pressed, led0 will be toggled. To stop the listener, call it’s deactivate method:

>>> listener.deactivate()

The Event object has some interesting attributes. You can access them like so:

>>> import pifacedigitalio
>>> pifacedigital = pifacedigitalio.PiFaceDigital()
>>> listener = pifacedigitalio.InputEventListener(chip=pifacedigital)
>>> listener.register(0, pifacedigitalio.IODIR_RISING_EDGE, print)
>>> listener.activate()

This would print out the event information whenever you un-press switch 0:

interrupt_flag:    0b1
interrupt_capture: 0b11111111
pin_num:           0
direction:         1
chip:              <pifacedigitalio.core.PiFaceDigital object at 0xb682dab0>
timestamp:         1380893579.447889

Exit from interrupt¶

In some cases you may want to deactivate the listener and exit your program on an interrupt (press switch to exit, for example). Since each method registered to an interrupt is run in a new thread and you can only deactivate a listener from within the same thread that activated it, you cannot deactivate a listener from a method registered to an interrupt. That is, you cannot do the following because the deactivate_listener_and_exit() method is started in a different thread:

import sys
import pifacedigitalio


listener = None


def deactivate_listener_and_exit(event):
    global listener
    listener.deactivate()
    sys.exit()


pifacedigital = pifacedigitalio.PiFaceDigital()
listener = pifacedigitalio.InputEventListener(chip=pifacedigital)
listener.register(0,
                  pifacedigitalio.IODIR_FALLING_EDGE,
                  deactivate_listener_and_exit)
listener.activate()

One solution is to use a Barrier synchronisation object. Each thread calls wait() on the barrier and then blocks. After the final thread calls wait() all threads are unblocked. Here is an example program which successfully exits on an interrupt:

import sys
import threading
import pifacedigitalio


exit_barrier = threading.Barrier(2)


def deactivate_listener_and_exit(event):
    global exit_barrier
    exit_barrier.wait()


pifacedigital = pifacedigitalio.PiFaceDigital()
listener = pifacedigitalio.InputEventListener(chip=pifacedigital)
listener.register(0,
                  pifacedigitalio.IODIR_FALLING_EDGE,
                  deactivate_listener_and_exit)
listener.activate()
exit_barrier.wait() # program will wait here until exit_barrier releases
listener.deactivate()
sys.exit()

Simple Web Control¶

You can control PiFace Digital from a web browser (or any network enabled device) using the simplewebcontrol.py tool.

You can start the tool by running the following command on your Raspberry Pi:

$ python3 /usr/share/doc/python3-pifacedigitalio/examples/simplewebcontrol.py

This will start a simple web server on port 8000 which you can access using a web browser.

Type the following into the address bar of a browser on any machine in the local network:

http://192.168.1.3:8000

Note

Relace 192.168.1.3 with the IP address of your Raspberry Pi.

It will return a JSON object describing the current state of PiFace Digital:

{'input_port': 0, 'output_port': 0}

Controlling Output¶

You can set the output port using the URL:

http://192.168.1.61:8000/?output_port=0xaa

Changing Port¶

You can specify which port you would like simplewebcontrol.py to use by passing the port number as the first argument:

$ python3 /usr/share/doc/python3-pifacedigitalio/examples/simplewebcontrol.py 12345

Reference¶

Note

Functions and classes in pifacedigitalio.core have been imported into the main namespace. pifacedigitalio.digital_write() is the same as pifacedigitalio.core.digital_write().

class pifacedigitalio.core.InputEventListener(chip=None, daemon=False)¶

Listens for events on the input port and calls the mapped callback functions.

>>> def print_flag(event):
...     print(event.interrupt_flag)
...
>>> listener = pifacedigitalio.InputEventListener()
>>> listener.register(0, pifacedigitalio.IODIR_ON, print_flag)
>>> listener.activate()

class pifacedigitalio.core.PiFaceDigital(hardware_addr=0, bus=0, chip_select=0, init_board=True)¶

A PiFace Digital board.

Attribute:	input_pins – list containing `pifacecommon.mcp23s17.MCP23S17RegisterBitNeg`.
Attribute:	input_port – See `pifacecommon.mcp23s17.MCP23S17RegisterNeg`.
Attribute:	output_pins – list containing `pifacecommon.mcp23s17.MCP23S17RegisterBit`.
Attribute:	output_port – See `pifacecommon.mcp23s17.MCP23S17Register`.
Attribute:	leds – list containing `pifacecommon.mcp23s17.MCP23S17RegisterBit`.
Attribute:	relays – list containing `pifacecommon.mcp23s17.MCP23S17RegisterBit`.
Attribute:	switches – list containing `pifacecommon.mcp23s17.MCP23S17RegisterBit`.

Example:

>>> pfd = pifacedigitalio.PiFaceDigital()
>>> pfd.input_port.value
0
>>> pfd.output_port.value = 0xAA
>>> pfd.leds[5].turn_on()

pifacedigitalio.core.deinit(bus=0, chip_select=0)¶

Stops interrupts on all boards. Only required when using digital_read() and digital_write().

Parameters:	bus (int) – SPI bus /dev/spidev<bus>.<chipselect> (default: {bus}) chip_select (int) – SPI chip select /dev/spidev<bus>.<chipselect> (default: {chip})

pifacedigitalio.core.digital_read(pin_num, hardware_addr=0)¶

Returns the value of the input pin specified.

Note

This function is for familiarality with users of other types of IO board. Consider accessing the input_pins attribute of a PiFaceDigital object:

>>> pfd = PiFaceDigital(hardware_addr)
>>> pfd.input_pins[pin_num].value
0

Parameters:	pin_num (int) – The pin number to read. hardware_addr (int) – The board to read from (default: 0)
Returns:	int – value of the pin

pifacedigitalio.core.digital_read_pullup(pin_num, hardware_addr=0)¶

Returns the value of the input pullup specified.

Note

This function is for familiarality with users of other types of IO board. Consider accessing the gppub attribute of a PiFaceDigital object:

>>> pfd = PiFaceDigital(hardware_addr)
>>> hex(pfd.gppub.value)
0xff
>>> pfd.gppub.bits[pin_num].value
1

Parameters:	pin_num (int) – The pin number to read. hardware_addr (int) – The board to read from (default: 0)
Returns:	int – value of the pin

pifacedigitalio.core.digital_write(pin_num, value, hardware_addr=0)¶

Writes the value to the input pin specified.

Note

This function is for familiarality with users of other types of IO board. Consider accessing the output_pins attribute of a PiFaceDigital object:

>>> pfd = PiFaceDigital(hardware_addr)
>>> pfd.output_pins[pin_num].value = 1

Parameters:	pin_num (int) – The pin number to write to. value (int) – The value to write. hardware_addr (int) – The board to read from (default: 0)

pifacedigitalio.core.digital_write_pullup(pin_num, value, hardware_addr=0)¶

Writes the value to the input pullup specified.

Note

This function is for familiarality with users of other types of IO board. Consider accessing the gppub attribute of a PiFaceDigital object:

>>> pfd = PiFaceDigital(hardware_addr)
>>> hex(pfd.gppub.value)
0xff
>>> pfd.gppub.bits[pin_num].value = 1

Parameters:	pin_num (int) – The pin number to write to. value (int) – The value to write. hardware_addr (int) – The board to read from (default: 0)

Welcome to PiFace Digital I/O’s documentation!¶

PiFace Digital¶

Outputs¶

LEDs¶

Relays¶

Inputs¶

Installation¶

Emulator¶

Examples¶

Basic usage¶

Interrupts¶

Exit from interrupt¶

Simple Web Control¶

Controlling Output¶

Changing Port¶

Reference¶

Indices and tables¶