Expander Pi Python Library

Python Library to use with Expander Pi board.

The Expander Pi contains separate classes for the real-time clock, analogue to digital converter, digital to analogue converter and 16 digital I/O pins. Examples are included to show how each of the classes can be used.

The Expander Pi uses the following devices:

• Maxim DS1307 Real-time Clock (RTC)
• Microchip MCP3208 8-channel 12-bit resolution analogue input (ADC)
• Microchip MCP4822 2 channel 12-bit resolution analogue output (DAC)
• Microchip MCP23017 16-channel digital I/O controller

The example python files can be found in /ABElectronics_Python_Libraries/ExpanderPi/demos

Downloading and Installing the library

To download to your Raspberry Pi type in the terminal:

git clone https://github.com/abelectronicsuk/ABElectronics_Python_Libraries.git

To install the python library navigate into the ABElectronics_Python_Libraries folder and run:

For Python 2.7:

sudo python setup.py install

For Python 3:

sudo python3 setup.py install

If you have PIP installed you can install the library directly from GitHub with the following command:

For Python 2.7:

sudo python2.7 -m pip install git+https://github.com/abelectronicsuk/ABElectronics_Python_Libraries.git

For Python 3:

sudo python3 -m pip install git+https://github.com/abelectronicsuk/ABElectronics_Python_Libraries.git

The Expander Pi library is located in the ExpanderPi directory

The library requires smbus2 or python-smbus to be installed.

For Python 2.7:

sudo pip install smbus2

For Python 3:

sudo pip3 install smbus2

Class: ADC

The ADC class controls the functions on the 12-bit 8-channel Analogue to Digital converter. The Expander Pi comes with an onboard 4.096 voltage reference. To use an external voltage reference, remove the solder bridge from jumper J1 and connect the external voltage reference to the Vref pin.

ADC Functions:

read_adc_voltage(channel, mode) 

Read the voltage from the selected channel on the ADC
Parameters: channel - options are: 1 to 8, mode = 0 or 1 - 0 = single-ended, 1 = differential
Returns: voltage

In single-ended mode, the channel number corresponds to the number on the Expander Pi.
In differential mode, the channel number selects the channels as follows:

read_adc_raw(channel, mode) 

Read the raw value from the selected channel on the ADC
Parameters: channel = options are: 1 to 8 , mode = 0 or 1 - 0 = single-ended, 1 = differential
Returns: raw 12-bit value (0 to 4096)

In single-ended mode, the channel number corresponds to the number on the Expander Pi. In differential mode, the channel the number selects the channels as follows:

set_adc_refvoltage(voltage) 

set the reference voltage for the analogue to digital converter.
By default, the ADC uses an onboard 4.096V voltage reference. If you choose to use an external voltage reference you will need to use this method to set the ADC reference voltage to match the supplied reference voltage. The reference voltage must be less than or equal to the voltage on the Raspberry Pi 5V rail.

Parameters: voltage (use a decimal number)
Returns: null

ADC Usage

To use the ADC class in your code you must first import the library:

from ExpanderPi import ADC

Next, you must initialise the ADC object:

adc = ADC()

If you are using an external voltage reference set the voltage using:

adc.set_adc_refvoltage(4.096)

Read the voltage from the ADC channel 1 in single-ended mode at 1-second intervals:

while (True):
  print adc.read_adc_voltage(1,0)
  time.sleep(1)

Class: DAC

The DAC class controls the 2-channel 12-bit digital-to-analogue converter. The DAC uses an internal voltage reference and can output a voltage between 0 and 2.048V. A gain setting allows you to increase the voltage to between 0 and 4.095V when the gain is set to 2

DAC Functions:

set_dac_voltage(channel, voltage)

Set the voltage for the selected channel on the DAC
Parameters:
channel - 1 or 2, the voltage can be between 0 and 2.047 volts when the gain is set to 1 or 0 and 4.095 volts when the gain is set to 2
Returns: null

set_dac_raw(channel, value)

Set the raw value from the selected channel on the DAC
Parameters:
channel - 1 or 2, value int between 0 and 4095
Returns: null

DAC Usage

To use the DAC class in your code you must first import the library:

from ExpanderPi import DAC

Next, you must initialise the DAC object with a gain setting of 1 or 2:

dac = DAC(1)

Set the channel and voltage for the DAC output.

dac.set_dac_voltage(1, 1.5)

Class: IO

The IO class controls the 16 digital I/O channels on the Expander Pi. The MCP23017 chip is split into two 8-bit ports. Port 0 controls pins 1 to 8 while Port 1 controls pins 9 to 16. When writing to or reading from a port the least significant bit represents the lowest numbered pin on the selected port.

Note: Microchip recommends that pin 8 (GPA7) and pin 16 (GPB7) are used as outputs only. This change was made for revision D MCP23017 chips manufactured after June 2020. See the MCP23017 datasheet for more information.

IO(initialise, bus)

Parameters:
initialise (optional): True = direction set as inputs, pullups disabled, ports not inverted. False = device state unaltered., defaults to True
bus (optional): I2C bus number (integer). If no value is set the class will try to find the I2C bus automatically using the device name.

IO Functions:

set_pin_direction(pin, value):

Sets the IO direction for an individual pin
Parameters:
pin: 1 to 16
value: 1 = input, 0 = output
Returns: null

get_pin_direction(pin)

Get the IO direction for an individual pin
Parameters:
pin: pin to read, 1 to 16
Returns: 1 = input, 0 = output

set_port_direction(port, value): 

Sets the IO direction for the specified IO port
Parameters:
port: 0 = pins 1 to 8, 1 = pins 9 to 16
value: number between 0 and 255 or 0x00 and 0xFF. Each bit in the 8-bit number represents a pin on the port. 1 = input, 0 = output
Returns: null

get_port_direction(port): 

Get the direction from an IO port
Parameters:
port: 0 = pins 1 to 8, 1 = pins 9 to 16
Returns: number between 0 and 255 (0xFF)

set_bus_direction(value): 

Sets the IO direction for all pins on the bus
Parameters:
value: 16-bit number 0 to 65535 (0xFFFF). For each bit 1 = input, 0 = output
Returns: null

get_bus_direction()

Get the direction for an IO bus
Returns: 16-bit number 0 to 65535 (0xFFFF). For each bit 1 = input, 0 = output

set_pin_pullup(pin, value)

Set the internal 100K pullup resistors for an individual pin
Parameters:
pin: pin to update, 1 to 16 value: 1 = enabled, 0 = disabled
Returns: null

get_pin_pullup(pin)

Get the internal 100K pullup resistors for an individual pin
Parameters:
pin: pin to read, 1 to 16
Returns: 1 = enabled, 0 = disabled

set_port_pullups(port, value)

Set the internal 100K pullup resistors for the selected IO port
Parameters:
port: 0 = pins 1 to 8, 1 = pins 9 to 16
value: number between 0 and 255 or 0x00 and 0xFF. Each bit in the 8-bit number represents a pin on the port. 1 = Enabled, 0 = Disabled
Returns: null

get_port_pullups(port): 

Get the internal pullup status for the selected IO port
Parameters:
port: 0 = pins 1 to 8, 1 = pins 9 to 16
Returns: number between 0 and 255 (0xFF)

set_bus_pullups(value)

Set internal 100K pullup resistors for an IO bus
Parameters:
value: 16-bit number 0 to 65535 (0xFFFF). For each bit 1 = enabled, 0 = disabled
Returns: null

get_bus_pullups()

Get the internal 100K pullup resistors for an IO bus
Returns: 16-bit number 0 to 65535 (0xFFFF). For each bit 1 = enabled, 0 = disabled

write_pin(pin, value)

Write to an individual pin 1 - 16
Parameters:
pin: 1 to 16
value: 1 = logic high, 0 = logic low
Returns: null

write_port(port, value)

Write to all pins on the selected port
Parameters:
port: 0 = pins 1 to 8, 1 = pins 9 to 16
value: number between 0 and 255 or 0x00 and 0xFF. Each bit in the 8-bit number represents a pin on the port. 1 = logic high, 0 = logic low
Returns: null

write_bus(value)

Write to all pins on the selected bus
Parameters:
value: 16-bit number 0 to 65535 (0xFFFF). For each bit 1 = logic high, 0 = logic low
Returns: null

read_pin(pin)

Read the value of an individual pin 1 - 16
Parameters:
pin: 1 to 16
Returns: 0 = logic low, 1 = logic high

read_port(port)

Read all pins on the selected port
Parameters:
port: 0 = pins 1 to 8, 1 = pins 9 to 16
Returns: number between 0 and 255 or 0x00 and 0xFF. Each bit in the 8-bit number represents a pin on the port. 0 = logic low, 1 = logic high

read_bus()

Read all pins on the bus
Returns: 16-bit number 0 to 65535 (0xFFFF) Each bit in the 16-bit number represents a pin on the port. 0 = logic low, 1 = logic high

invert_pin(pin, value)

Invert the polarity of the selected pin
Parameters:
pin: 1 to 16
value: 0 = same logic state of the input pin, 1 = inverted logic state of the input pin
Returns: null

get_pin_polarity(pin)

Get the polarity of the selected pin
Parameters:
pin: pin to read, 1 to 16
Returns: 0 = same logic state of the input pin, 1 = inverted logic state of the input pin

invert_port(port, value)

Invert the polarity of the pins on a selected port
Parameters:
port: 0 = pins 1 to 8, 1 = pins 9 to 16
value: number between 0 and 255 or 0x00 and 0xFF. Each bit in the 8-bit number represents a pin on the port. 0 = same logic state of the input pin, 1 = inverted logic state of the input pin
Returns: null

get_port_polarity(port): 

Get the polarity for the selected IO port
Parameters:
port: 0 = pins 1 to 8, 1 = pins 9 to 16
Returns: number between 0 and 255 (0xFF)

invert_bus(value)

Invert the polarity of the pins on the bus
Parameters:
value: 16-bit number 0 to 65535 (0xFFFF). For each bit 0 = same logic state of the input pin, 1 = inverted logic state of the input pin
Returns: null

get_bus_polarity()

Get the polarity of the pins on the bus
Returns: 16-bit number 0 to 65535 (0xFFFF). For each bit 0 = same logic state of the input pin, 1 = inverted logic state of the input pin

mirror_interrupts(value)

Sets whether the interrupt pins INT A and INT B are independently connected to each port or internally connected
Parameters:
value: 1 = The INT pins are internally connected, 0 = The INT pins are not connected. INT A is associated with PortA and INT B is associated with PortB
Returns: null

set_interrupt_polarity(value)

Sets the polarity of the INT output pins
Parameters:
value: 0 = Active Low, 1 = Active High
Returns: null

get_interrupt_polarity()

Get the polarity of the INT output pins
Returns: 1 = Active-high. 0 = Active-low.

set_interrupt_type(port, value)

Sets the type of interrupt for each pin on the selected port
Parameters:
port: 0 = pins 1 to 8, 1 = pins 9 to 16
value: number between 0 and 255 or 0x00 and 0xFF. Each bit in the 8-bit number represents a pin on the port. 1 = interrupt is fired when the pin matches the default value, 0 = the interrupt is fired on state change
Returns: null

get_interrupt_type(port): 

Get the type of interrupt for each pin on the selected port
Parameters:
port: 0 = pins 1 to 8, 1 = pins 9 to 16
Returns: number between 0 and 255 (0xFF)
For each bit 1 = interrupt is fired when the pin matches the default value, 0 = interrupt fires on state change

set_interrupt_defaults(port, value)

These bits set the compare value for pins configured for interrupt-on-change on the selected port.
If the associated pin level is the opposite of the register bit, an interrupt occurs.
Parameters:
port: 0 = pins 1 to 8, 1 = pins 9 to 16, value: compare value between 0 and 255 or 0x00 and 0xFF. Each bit in the 8-bit number represents a pin on the port.
Returns: null

get_interrupt_defaults(port): 

Get the interrupt default value for each pin on the selected port
Parameters:
port: 0 = pins 1 to 8, 1 = pins 9 to 16
Returns: number between 0 and 255 (0xFF)

set_interrupt_on_pin(pin, value)

Enable interrupts for the selected pin
Parameters:
pin: 1 to 16
value: 0 = interrupt disabled, 1 = interrupt enabled
Returns: null

get_interrupt_on_pin(pin)

Gets whether the interrupt is enabled for the selected pin
Parameters:
pin: pin to read, 1 to 16
Returns: 1 = enabled, 0 = disabled

set_interrupt_on_port(port, value)

Enable interrupts for the pins on the selected port
Parameters:
port: 0 = pins 1 to 8, 1 = pins 9 to 16
value: number between 0 and 255 or 0x00 and 0xFF. Each bit in the 8-bit number represents a pin on the port.
Returns: null

get_interrupt_on_port(port): 

Gets whether the interrupts are enabled for the selected port
Parameters:
port: 0 = pins 1 to 8, 1 = pins 9 to 16
Returns: number between 0 and 255 (0xFF). For each bit 1 = enabled, 0 = disabled

set_interrupt_on_bus(value)

Enable interrupts for the pins on the bus
Parameters:
value: 16-bit number 0 to 65535 (0xFFFF). For each bit 1 = enabled, 0 = disabled
Returns: null

get_interrupt_on_bus()

Gets whether the interrupts are enabled for the bus
Returns: 16-bit number 0 to 65535 (0xFFFF). For each bit 1 = enabled, 0 = disabled

read_interrupt_status(port)

Read the interrupt status for the pins on the selected port
Parameters:
port: 0 = pins 1 to 8, 1 = pins 9 to 16
Returns: number between 0 and 255 or 0x00 and 0xFF. Each bit in the 8-bit number represents a pin on the port. 1 = Enabled, 0 = Disabled

read_interrupt_capture(port)

Read the value from the selected port at the time of the last interrupt trigger
Parameters:
port: 0 = pins 1 to 8, 1 = pins 9 to 16
Returns: number between 0 and 255 or 0x00 and 0xFF. Each bit in the 8-bit number represents a pin on the port. 1 = Enabled, 0 = Disabled

reset_interrupts()

Set the interrupts A and B to 0
Parameters: null
Returns: null

IO Usage

To use the IO Pi library in your code you must first import the library:

from ExpanderPi import IO

Next, you must initialise the IO object:

io = IO()

By default the IO object will be initialised in a reset state with the ports set as inputs, pullup resistors disabled and the pins non-inverted. If you want to initialise the IO object without updating the port direction or the pullup status you can add a reset=False parameter.

io = IO(reset=False)

We will read the inputs 1 to 8 from the I/O bus so set port 0 as inputs and enable the internal pullup resistors

io.set_port_direction(0, 0xFF)
io.set_port_pullups(0, 0xFF)

You can now read pin 1 with:

print 'Pin 1: ' + str(io.read_pin(1))

Class: RTC

The RTC class controls the DS1307 real-time clock on the Expander Pi. You can set and read the date and time from the clock as well as control the pulse output on the RTC pin.

RTC(bus)

Parameters:
bus (optional): I2C bus number (integer). If no value is set the class will try to find the i2c bus automatically using the device name.

RTC Functions:

set_date(date) 

Set the date and time on the RTC in ISO 8601 format - YYYY-MM-DDTHH:MM:SS
Parameters: date
Returns: null

read_date() 

Returns the date from the RTC in ISO 8601 format - YYYY-MM-DDTHH:MM:SS
Returns: date

enable_output() 

Enable the square-wave output on the SQW pin.
Returns: null

disable_output()

Disable the square-wave output on the SQW pin.
Returns: null

set_frequency(frequency)

Set the frequency for the square-wave output on the SQW pin.
Parameters: frequency - options are: 1 = 1Hz, 2 = 4.096KHz, 3 = 8.192KHz, 4 = 32.768KHz
Returns: null

write_memory(address, valuearray)

Write to the memory on the ds1307. The ds1307 contains 56-Byte, battery-backed RAM with Unlimited Writes
Parameters: address - 0x08 to 0x3F
valuearray - byte array containing data to be written to memory
Returns: null

read_memory(address, length)

Read from the memory on the ds1307
Parameters: address - 0x08 to 0x3F length - up to 32 bytes.
length can not exceed the available address space.
Returns: array of bytes

RTC Usage

To use the RTC class in your code you must first import the library:

from ExpanderPi import RTC

Next, you must initialise the RTC object:

rtc = RTC()

Set the date using ISO 8601 format - YYYY-MM-DDTHH:MM:SS :

rtc.set_date("2013-04-23T12:32:11")

Enable the square-wave output at 8.192KHz on the SQW pin:

rtc.set_frequency(3)
rtc.enable_output()

Read the current date and time from the RTC at 1-second intervals:

while (True):
  print rtc.read_date()
  time.sleep(1)