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