Expander Pi Node JS Library

Node.js Library to use with Expander Pi Raspberry Pi development board.

Note: Microchip recommends that digital pins 8 (GPA7) and 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.

Install

To download to your Raspberry Pi type in the terminal:

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

The IO Pi library is located in the /lib/expanderpi/ directory

The example files are located in the /examples/expanderpi/ directory

The Expander Pi library requires the rpio and i2c-bus libraries to run.

Install rpio from npm package repository rpio with

npm install rpio

Install i2c-bus from npm package repository i2c-bus with

npm install i2c-bus

The Expander Pi library is split up into four classes, ADC, DAC, IO and RTC.

Expander Pi ADC

The ExpanderPiADC class controls the MCP3208 12-bit ADC.

ADC Functions

readADCVoltage(channel, mode) 

Read the voltage from the selected channel on the ADC
Parameters: channel - 1 or 2; mode - 0 = single-ended, 1 = differential
Returns: number as a float between 0 and 2.048

readADCRaw(channel, mode) 

Read the raw value from the selected channel on the ADC
Parameters: channel - 1 or 2; mode - 0 = single-ended, 1 = differential
Returns: int

setADCRefVoltage(voltage)

Set the reference voltage for the analogue to digital converter.
The ADC uses the raspberry pi 3.3V power as a voltage reference so using this method to set the reference to match the exact output voltage from the 3.3V regulator will increase the accuracy of the ADC readings.
Parameters: voltage - float between 0.0 and 7.0
Returns: null

ADC Usage

To use the ExpanderPiADC class in your code you must first import the Expander Pi library:

var expanderpi = require('../../lib/expanderpi/expanderpi');

Next you must initialise the ExpanderPiADC object:

var adc = new ExpanderPiADC();

Set the reference voltage.

adc.setADCRefVoltage(4.096);

Read the voltage from channel 1 and display it on the screen

console.log('Reading 1 Voltage: ' + adc.readADCVoltage(1, 0));

Expander Pi DAC

The ExpanderPiDAC class controls the MCP4822 12-bit DAC.

DAC Functions

setDACVoltage(channel, voltage)

Set the voltage for the selected channel on the DAC. The DAC has two gain values, 1 or 2, which can be set when the ADCDAC object is created. A gain of 1 will give a voltage between 0 and 2.047 volts. A gain of 2 will give a voltage between 0 and 4.096 volts.
Parameters: channel - 1 or 2, voltage - sets the voltage for the selected channel.
Returns: null

setDACRaw(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

setDACGain(gain)

Set the gain for the DAC. This is used to set the output based on the reference voltage of 2.048V.
When the gain is set to 2 the maximum voltage will be approximately 4.096V.
Parameters: gain - 1 or 2
Returns: null

DAC Usage

To use the ExpanderPiDAC class in your code you must first import the Expander Pi library:

var expanderpi = require('../../lib/expanderpi/expanderpi');

Next, you must initialise the ExpanderPiDAC object:

var dac = new ExpanderPiDAC();

Set the DAC gain to be 1

dac.setDACGain(1);

Set the voltage on channel 1 as 0.8V and channel 2 as 1.5V.

dac.setDACVoltage(1, 0.8);
dac.setDACVoltage(2, 1.5);

ExpanderPi IO

The ExpanderPiIO class controls the MCP23017 16-pin I/O controller.

IO Functions

setPinDirection(pin, direction):

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

setPortDirection(port, direction): 

Sets the IO direction for the specified IO port
Parameters: port - 0 = pins 1 to 8, port 1 = pins 9 to 16, direction - 1 = input, 0 = output
Returns: null

setPinPullup(pin, value)

Set the internal 100K pull-up resistors for an individual pin Parameters: pin - 1 to 16, value: 1 = Enabled, 0 = Disabled
Returns: null

setPortPullups(port, value)

Set the internal 100K pull-up resistors for the selected IO port
Parameters: port - 0 or 1, value: 0x00 to 0xFF
Returns: null

writePin(pin, value)

Write to an individual pin 1 - 16
Parameters: pin - 1 to 16, value - 1 = Enabled, 0 = Disabled
Returns: null

writePort(self, port, value)

Write to all pins on the selected port
Parameters: port - 0 = pins 1 to 8, port 1 = pins 9 to 16, value - number between 0 and 255 or 0x00 and 0xFF
Returns: null

readPin(pin)

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

readPort(port)

Read all pins on the selected port
Parameters: port - 0 = pins 1 to 8, port 1 = pins 9 to 16
Returns: number between 0 and 255 or 0x00 and 0xFF

invertPort(port, polarity)

Invert the polarity of the pins on a selected port
Parameters: port - 0 = pins 1 to 8, port 1 = pins 9 to 16, polarity - 0 = same logic state of the input pin, 1 = inverted logic state of the input pin
Returns: null

invertPin(pin, polarity)

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

mirrorInterrupts(value)

Mirror Interrupts
Parameters: value - 1 = The INT pins are internally connected, 0 = The INT pins are not connected. INTA is associated with PortA and INTB is associated with PortB
Returns: null

setInterruptType(port, value)

Sets the type of interrupt for each pin on the selected port
Parameters: port 0 = pins 1 to 8, port 1 = pins 9 to 16, value: 1 = interrupt is fired when the pin matches the default value, 0 = the interrupt is fired on state change
Returns: null

setInterruptPolarity(value)

This sets the polarity of the INT output pins Parameters: 1 = Active-high, 0 = Active-low Returns: null

setInterruptDefaults(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, port 1 = pins 9 to 16, value: compare value
Returns: null

setInterruptOnPort(port, value)

Enable interrupts for the pins on the selected port
Parameters: port 0 = pins 1 to 8, port 1 = pins 9 to 16, value: number between 0 and 255 or 0x00 and 0xFF
Returns: null

setInterruptOnPin(pin, value)

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

readInterruptStatus(port)

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

readInterruptCapture(port)

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

resetInterrupts()

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

IO Usage

To use the ExpanderPiIO class in your code you must first import the Expander Pi library:

var expanderpi = require('../../lib/expanderpi/expanderpi');

Next, you must initialise the ExpanderPiIO object

var bus = new ExpanderPiIO();

We will read the inputs 1 to 8 from bus 1 so set port 0 as inputs and enable the internal pull-up resistors

bus.setPortDirection(0, 0xFF);
bus.setPortPullups(0, 0xFF);

You can now read pin 1 with:

console.log('Pin 1: %d', bus.readPin(1));

ExpanderPi RTC

The ExpanderPiRTC class controls the DS1307 real-time clock.

RTC Functions:

setDate(date) 

Set the date and time on the RTC using a javascript Date object
Parameters: date
Returns: null

readDate() 

Returns the date from the RTC as a javascript Date object
Returns: date object

enableOutput() 

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

disableOutput()

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

setFrequency(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

writeMemory(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
Parameters: valuearray - byte array (Uint8Array) containing data to be written to memory
Returns: null

readMemory(address, valuearray)

Read from the memory on the DS1307. The DS1307 contains 56 - Byte, battery-backed RAM with Unlimited Writes
Parameters: address - 0x08 to 0x3F
Parameters: length - Up to 32 bytes. length can not exceed the available address space.
Returns: Returns a Uint8Array type array of the data read from memory

RTC Usage

To use the ExpanderPiRTC class in your code you must first import the Expander Pi library:

var expanderpi = require('../../lib/expanderpi/expanderpi');

Next, you must create an ExpanderPiRTC object:

var rtc = new ExpanderPiRTC();

Set the current time using a date object:

var d = new Date(2016, 07, 04, 10, 23, 00, 00);
rtc.setDate(d);

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:

var myClock = setInterval(clockTimer, 1000);

function clockTimer() {    
    console.log(rtc.readDate().toISOString());
}