Expander Pi Library for C++

C++ Library to use with Expander Pi board.

The Expander Pi class contains methods for controlling the real-time clock, analogue-to-digital converter, digital-to-analogue converter and digital I/O pins. Examples are included to show the class can be used.

The example demo files can be found in /ABElectronics_CPP_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_CPP_Libraries.git

Class: ExpanderPi

ExpanderPi(bool init)

Initialise the Expander Pi Object
Parameter:
init (bool optional): initialise the IO chip. Defaults to true.
usertc (bool optional): initialise the RTC chip. Set to false when using the RTC with the Linux ds1307 module

When the IO is initialised the pins will be set as inputs and non-inverted. Pullup resistors are disabled.

ADC Methods:

The ADC methods control 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.

int adc_open();

Open the ADC SPI bus channel. This needs to be called before using the ADC.
Returns: null

void adc_close();

Close the ADC SPI bus channel
Returns: null

adc_read_voltage(int channel, int mode) 

Read the voltage from the selected channel on the ADC.
Parameters:
channel (int): options: 1 to 8.
mode (int): 0 = Single Ended or 1 = Differential
Returns: voltage (double) between 0V and the reference voltage

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

adc_read_raw(int channel, int mode)

Read the raw value from the selected channel on the ADC.
Parameters:
channel (int): options: 1 to 8.
mode (int): 0 = Single Ended or 1 = Differential
Returns: (int) 12-bit value (0 to 4096)

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

adc_set_refvoltage(double ref) 

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:
ref (double): reference voltage
Returns: null

DAC Methods:

The DAC methods control 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 with the gain set to 1 or 0 and 4.095V when the gain is set to 2.

dac_open()

Open the DAC SPI bus channel. This needs to be called before using the DAC.
Returns: null

dac_close()

Close the DAC SPI bus channel
Returns: null

dac_set_voltage(double voltage, int channel, int gain)

Set the voltage for the selected channel on the DAC.
Parameters:
voltage (double): 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
channel (int): 1 or 2
gain (int): 1 or 2. The output voltage will be between 0 and 2.048V when the gain is set to 1, 0 and 4.096V when the gain is set to 2
Returns: null

dac_set_raw(uint16_t raw, int channel, int gain)

Set the raw value from the selected channel on the DAC.
Parameters:
raw (int): value between 0 and 4095
channel (int): 1 or 2
gain (int): 1 or 2. The output voltage will be between 0 and 2.048V when the gain is set to 1, 0 and 4.096V when the gain is set to 2
Returns: null

IO Methods

The IO methods control the MCP23017 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_set_pin_direction(uint8_t pin, uint8_t direction):

Sets the IO direction for an individual pin.
Parameters:
pin (uint8_t): 1 to 16
direction (uint8_t): 1 = input, 0 = output
Returns: null

io_get_pin_direction(uint8_t pin)

Get the IO direction for an individual pin.
Parameters:
pin (uint8_t): pin to read, 1 to 16
Returns: (uint8_t) 1 = input, 0 = output

io_set_port_direction(uint8_t port, uint8_t direction): 

Sets the IO direction for the specified IO port.
Parameters:
port (uint8_t): 0 = pins 1 to 8, 1 = pins 9 to 16
direction (uint8_t): 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

io_get_port_direction(uint8_t port): 

Get the direction from an IO port.
Parameters:
port (uint8_t): 0 = pins 1 to 8, 1 = pins 9 to 16
Returns: (uint8_t) number between 0 and 255 (0xFF)

io_set_bus_direction(uint16_t direction): 

Sets the IO direction for all pins on the bus.
Parameters:
direction (uint16_t): 16-bit number 0 to 65535 (0xFFFF). For each bit 1 = input, 0 = output
Returns: null

io_get_bus_direction()

Get the direction for an IO bus.
Returns: (uint16_t) 16-bit number 0 to 65535 (0xFFFF). For each bit 1 = input, 0 = output

io_set_pin_pullup(uint8_t pin, uint8_t value)

Set the internal 100K pull-up resistors for an individual pin.
Parameters:
pin (uint8_t): pin to update, 1 to 16 value (uint8_t): 1 = enabled, 0 = disabled
Returns: null

io_get_pin_pullup(uint8_t pin)

Get the internal 100K pull-up resistors for an individual pin.
Parameters:
pin (uint8_t): pin to read, 1 to 16
Returns: (uint8_t) 1 = enabled, 0 = disabled

io_set_port_pullups(uint8_t port, uint8_t value)

Set the internal 100K pull-up resistors for the selected IO port.
Parameters:
port (uint8_t): 0 = pins 1 to 8, 1 = pins 9 to 16
value (uint8_t): 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

io_get_port_pullups(uint8_t port): 

Get the internal pull-up status for the selected IO port.
Parameters:
port (uint8_t): 0 = pins 1 to 8, 1 = pins 9 to 16
Returns: (uint8_t) number between 0 and 255 (0xFF)

io_set_bus_pullups(uint16_t value)

Set internal 100K pull-up resistors for an IO bus.
Parameters:
value (uint16_t): 16-bit number 0 to 65535 (0xFFFF). For each bit 1 = enabled, 0 = disabled
Returns: null

io_get_bus_pullups()

Get the internal 100K pull-up resistors for an IO bus.
Returns: (uint16_t) 16-bit number 0 to 65535 (0xFFFF). For each bit 1 = enabled, 0 = disabled

io_write_pin(uint8_t pin, uint8_t value)

Write to an individual pin 1 - 16.
Parameters:
pin (uint8_t): 1 to 16
value (uint8_t): 1 = logic high, 0 = logic low
Returns: null

io_write_port(uint8_t port, uint8_t value)

Write to all pins on the selected port.
Parameters:
port (uint8_t): 0 = pins 1 to 8, 1 = pins 9 to 16
value (uint8_t): 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

io_write_bus(uint16_t value)

Write to all pins on the selected bus.
Parameters:
value (uint16_t): 16-bit number 0 to 65535 (0xFFFF). For each bit 1 = logic high, 0 = logic low
Returns: null

io_read_pin(uint8_t pin)

Read the value of an individual pin 1 - 16.
Parameters:
pin (uint8_t): 1 to 16
Returns: (uint8_t) 0 = logic low, 1 = logic high

io_read_port(uint8_t port)

Read all pins on the selected port.
Parameters:
port (uint8_t): 0 = pins 1 to 8, 1 = pins 9 to 16
Returns: (uint8_t) 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

io_read_bus()

Read all pins on the bus.
Returns: (uint16_t) 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

io_invert_pin(uint8_t pin, uint8_t polarity)

Invert the polarity of the selected pin.
Parameters:
pin (uint8_t): 1 to 16
polarity (uint8_t): 0 = same logic state of the input pin, 1 = inverted logic state of the input pin
Returns: null

io_get_pin_polarity(uint8_t pin)

Get the polarity of the selected pin.
Parameters:
pin (uint8_t): pin to read, 1 to 16
Returns: (uint8_t) 0 = same logic state of the input pin, 1 = inverted logic state of the input pin

io_invert_port(uint8_t port, uint8_t polarity)

Invert the polarity of the pins on a selected port.
Parameters:
port (uint8_t): 0 = pins 1 to 8, 1 = pins 9 to 16
polarity (uint8_t): 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

io_get_port_polarity(uint8_t port): 

Get the polarity for the selected IO port.
Parameters:
port (uint8_t): 0 = pins 1 to 8, 1 = pins 9 to 16
Returns: (uint8_t) number between 0 and 255 (0xFF)

io_invert_bus(uint16_t polarity)

Invert the polarity of the pins on the bus.
Parameters:
polarity (uint16_t): 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

io_get_bus_polarity()

Get the polarity of the pins on the bus.
Returns: (uint16_t) 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

io_mirror_interrupts(uint8_t value)

Sets whether the interrupt pins INT A and INT B are independently connected to each port or internally connected.
Parameters:
value (uint8_t): 1 = The INT pins are internally connected, 0 = The INT pins are not connected. INT A is associated with Port A and INT B is associated with Port B.
Returns: null

io_set_interrupt_polarity(uint8_t value)

Sets the polarity of the INT output pins.
Parameters:
value (uint8_t): 0 = Active Low, 1 = Active High
Returns: null

io_get_interrupt_polarity()

Get the polarity of the INT output pins.
Returns: (uint8_t) 1 = Active-high. 0 = Active-low.

io_set_interrupt_type(uint8_t port, uint8_t value)

Sets the type of interrupt for each pin on the selected port.
Parameters:
port (uint8_t): 0 = pins 1 to 8, 1 = pins 9 to 16
value (uint8_t): 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

io_get_interrupt_type(uint8_t port): 

Get the type of interrupt for each pin on the selected port.
Parameters:
port (uint8_t): 0 = pins 1 to 8, 1 = pins 9 to 16
Returns: (uint8_t) 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

io_set_interrupt_defaults(uint8_t port, uint8_t 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 (uint8_t): 0 = pins 1 to 8, 1 = pins 9 to 16, value (uint8_t): 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

io_get_interrupt_defaults(uint8_t port): 

Get the interrupt default value for each pin on the selected port.
Parameters:
port (uint8_t): 0 = pins 1 to 8, 1 = pins 9 to 16
Returns: (uint8_t) number between 0 and 255 (0xFF)

io_set_interrupt_on_pin(uint8_t pin, uint8_t value)

Enable interrupts for the selected pin.
Parameters:
pin (uint8_t): 1 to 16
value (uint8_t): 0 = interrupt disabled, 1 = interrupt enabled
Returns: null

io_get_interrupt_on_pin(uint8_t pin)

Gets whether the interrupt is enabled for the selected pin.
Parameters:
pin (uint8_t): pin to read, 1 to 16
Returns: (uint8_t) 1 = enabled, 0 = disabled

io_set_interrupt_on_port(uint8_t port, uint8_t value)

Enable interrupts for the pins on the selected port.
Parameters:
port (uint8_t): 0 = pins 1 to 8, 1 = pins 9 to 16
value (uint8_t): number between 0 and 255 or 0x00 and 0xFF. Each bit in the 8-bit number represents a pin on the port.
Returns: null

io_get_interrupt_on_port(uint8_t port): 

Gets whether the interrupts are enabled for the selected port.
Parameters:
port (uint8_t): 0 = pins 1 to 8, 1 = pins 9 to 16
Returns: (uint8_t) number between 0 and 255 (0xFF). For each bit 1 = enabled, 0 = disabled

io_set_interrupt_on_bus(uint16_t value)

Enable interrupts for the pins on the bus.
Parameters:
value (uint16_t): 16-bit number 0 to 65535 (0xFFFF). For each bit 1 = enabled, 0 = disabled
Returns: null

io_get_interrupt_on_bus()

Gets whether the interrupts are enabled for the bus.
Returns: (uint16_t) 16-bit number 0 to 65535 (0xFFFF). For each bit 1 = enabled, 0 = disabled

io_read_interrupt_status(uint8_t port)

Read the interrupt status for the pins on the selected port.
Parameters:
port (uint8_t): 0 = pins 1 to 8, 1 = pins 9 to 16
Returns: (uint8_t) 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

io_read_interrupt_capture(uint8_t port)

Read the value from the selected port at the time of the last interrupt trigger.
Parameters:
port (uint8_t): 0 = pins 1 to 8, 1 = pins 9 to 16
Returns: (uint8_t) 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

io_reset_interrupts()

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

RTC methods

The RTC methods control 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_set_date(struct tm date) 

Set the date and time on the RTC.
Parameters:
date (struct tm): date and time
Returns: null

rtc_read_date() 

Returns the date from the RTC.
Returns: (tm struct) date

rtc_enable_output() 

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

rtc_disable_output()

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

rtc_set_frequency(uint8_t frequency)

Set the frequency for the square-wave output on the SQW pin.
Parameters:
frequency (uint8_t): options are: 1 = 1Hz, 2 = 4.096KHz, 3 = 8.192KHz, 4 = 32.768KHz
Returns: null

rtc_write_memory(uint8_t address, uint8_t *valuearray, uint8_t length)

Write to the memory on the ds1307. The ds1307 contains 56-Byte, battery-backed RAM with Unlimited Writes.
Parameters:
address (uint8_t): 0x08 to 0x3F
valuearray (uint8_t*): array containing data to be written to memory
length (uint8_t): up to 56 bytes. array length can not exceed the available address space
Returns: null

rtc_read_memory(uint8_t address, uint8_t length)

Read from the memory on the ds1307.
Parameters:
address (uint8_t): 0x08 to 0x3F
length (uint8_t): up to 56 bytes. length can not exceed the available address space
Returns: (uint8_t*) array of bytes from the SRAM