rpi-gpio

rpi-gpio.js

Control Raspberry Pi GPIO pins with node.js

Supported hardware

• Raspberry Pi 1 Model A
• Raspberry Pi 1 Model A+
• Raspberry Pi 1 Model B
• Raspberry Pi 1 Model B+
• Raspberry Pi 2 Model B
• Raspberry Pi 3 Model B
• Raspberry Pi Zero
• Raspberry Pi Zero W

Setup

See this guide on how to get node.js running on Raspberry Pi.

This module can then be installed with npm:

npm install rpi-gpio

Dependency

Please note that this module has a dependency on epoll and that currently it is only possible to build and develop the module on Linux systems.

If you are having trouble installing this module make sure you are running gcc/g++ -v 4.8 or higher. Here is an installation guide.

Usage

Before you can read or write, you must use setup() to open a channel, and must specify whether it will be used for input or output. Having done this, you can then read in the state of the channel or write a value to it using read() or write().

All of the functions relating to the pin state within this module are asynchronous, so where necessary - for example in reading the value of a channel - a callback must be provided. This module inherits the standard EventEmitter, so you may use its functions to listen to events.

Pin naming

Please be aware that there are multiple ways of referring to the pins on the Raspberry Pi. The simplest and default way to use the module is refer to them by physical position, using the diagrams on this page. So holding the Raspberry Pi such that the GPIO header runs down the upper-right side of the board, if you wished to address GPIO4 (which is in column 1 and row 4), you would setup pin 7. If you wish instead to refer to the pins by their GPIO names (known as BCM naming), you can use the setMode command described in the API documentation below.

Running without sudo

This module will work without use of the sudo command, as long as the user running the node process belongs to the gpio group. You can check the current user's groups by running the command groups, or groups <user> for another user. If you are not already a member of the gpio group, you can add yourself or another user by running sudo adduser <user> gpio.

API (Error-first)

The default API uses the node-style error-first callbacks to perform asynchronous functions. Most of these methods take a callback, and that callback should check for an error in its first argument. It is important to check for an error after each command, else your code will continue to run and will likely fail in hard to understand ways.

Methods

setup(channel [, direction, edge], callback)

Sets up a channel for read or write. Must be done before the channel can be used.

• channel: Reference to the pin in the current mode's schema.
• direction: The pin direction, pass either DIR_IN for read mode or DIR_OUT for write mode. You can also pass DIR_LOW or DIR_HIGH to use the write mode and specify an initial state of 'off' or 'on' respectively. Defaults to DIR_OUT.
• edge: Interrupt generating GPIO chip setting, pass in EDGE_NONE for no interrupts, EDGE_RISING for interrupts on rising values, EDGE_FALLING for interrupts on falling values or EDGE_BOTH for all interrupts. Defaults to EDGE_NONE.
• callback: Provides Error as the first argument if an error occurred.

read(channel, callback)

Reads the value of a channel.

• channel: Reference to the pin in the current mode's schema.
• callback: Provides Error as the first argument if an error occured, otherwise the pin value boolean as the second argument.

write(channel, value [, callback])

Writes the value of a channel.

• channel: Reference to the pin in the current mode's schema.
• value: Boolean value to specify whether the channel will turn on or off.
• callback: Provides Error as the first argument if an error occured.

setMode(mode)

Sets the channel addressing schema.

• mode: Specify either Raspberry Pi or SoC/BCM pin schemas, by passing MODE_RPI or MODE_BCM. Defaults to MODE_RPI.

input()

Alias of read().

output()

Alias of write().

destroy()

Tears down any previously set up channels.

reset()

Tears down the module state - used for testing.

Events

See Node EventEmitter for documentation on listening to events.

change

Emitted when the value of a channel changed

• channel
• value

API (Promises)

This API exposes a Promises interface to the module. All of the same functions are available, but do not take callbacks and instead return a Promise.

The Promises interface is available in the promise namespace, e.g.:

var gpio = require('rpi-gpio')
var gpiop = gpio.promise;

gpiop.setup(7, gpio.DIR_OUT)
    .then(() => {
        return gpiop.write(7, true)
    })
    .catch((err) => {
        console.log('Error: ', err.toString())
    })

Examples

Setup and read the value of a pin

var gpio = require('rpi-gpio');

gpio.setup(7, gpio.DIR_IN, readInput);

function readInput(err) {
    if (err) throw err;
    gpio.read(7, function(err, value) {
        if (err) throw err;
        console.log('The value is ' + value);
    });
}

Setup and write to a pin

var gpio = require('rpi-gpio');

gpio.setup(7, gpio.DIR_OUT, write);

function write(err) {
    if (err) throw err;
    gpio.write(7, true, function(err) {
        if (err) throw err;
        console.log('Written to pin');
    });
}

Setup and write to a pin that starts as on

This example shows how to setup the pin for write mode with the default state as "on". Why do this? It can sometimes be useful to reverse the default initial state due to wiring or uncontrollable circumstances.

var gpio = require('rpi-gpio');

gpio.setup(7, gpio.DIR_HIGH, write);

function write(err) {
    if (err) throw err;
    gpio.write(7, false, function(err) {
        if (err) throw err;
        console.log('Written to pin');
    });
}

Listen for changes on a pin

var gpio = require('rpi-gpio');

gpio.on('change', function(channel, value) {
	console.log('Channel ' + channel + ' value is now ' + value);
});
gpio.setup(7, gpio.DIR_IN, gpio.EDGE_BOTH);

Unexport pins opened by the module when finished

var gpio = require('../rpi-gpio');

gpio.on('export', function(channel) {
    console.log('Channel set: ' + channel);
});

gpio.setup(7, gpio.DIR_OUT);
gpio.setup(15, gpio.DIR_OUT);
gpio.setup(16, gpio.DIR_OUT, pause);

function pause() {
    setTimeout(closePins, 2000);
}

function closePins() {
    gpio.destroy(function() {
        console.log('All pins unexported');
    });
}

Voltage cycling a pin

This example shows how to set up a channel for output mode. After it is set up, it executes a callback which in turn calls another, causing the voltage to alternate up and down three times.

var gpio = require('rpi-gpio');

var pin   = 7;
var delay = 2000;
var count = 0;
var max   = 3;

gpio.setup(pin, gpio.DIR_OUT, on);

function on() {
    if (count >= max) {
        gpio.destroy(function() {
            console.log('Closed pins, now exit');
        });
        return;
    }

    setTimeout(function() {
        gpio.write(pin, 1, off);
        count += 1;
    }, delay);
}

function off() {
    setTimeout(function() {
        gpio.write(pin, 0, on);
    }, delay);
}

Using flow control modules

Due to the asynchronous nature of this module, using an asynchronous flow control module can help to simplify development. This example uses async.js to turn pins on and off in series.

var gpio = require('rpi-gpio');
var async = require('async');

async.parallel([
    function(callback) {
        gpio.setup(7, gpio.DIR_OUT, callback)
    },
    function(callback) {
        gpio.setup(15, gpio.DIR_OUT, callback)
    },
    function(callback) {
        gpio.setup(16, gpio.DIR_OUT, callback)
    },
], function(err, results) {
    console.log('Pins set up');
    write();
});

function write() {
    async.series([
        function(callback) {
            delayedWrite(7, true, callback);
        },
        function(callback) {
            delayedWrite(15, true, callback);
        },
        function(callback) {
            delayedWrite(16, true, callback);
        },
        function(callback) {
            delayedWrite(7, false, callback);
        },
        function(callback) {
            delayedWrite(15, false, callback);
        },
        function(callback) {
            delayedWrite(16, false, callback);
        },
    ], function(err, results) {
        console.log('Writes complete, pause then unexport pins');
        setTimeout(function() {
            gpio.destroy(function() {
                console.log('Closed pins, now exit');
            });
        }, 500);
    });
};

function delayedWrite(pin, value, callback) {
    setTimeout(function() {
        gpio.write(pin, value, callback);
    }, 500);
}

Contributing

Contributions are always appreciated, whether that's in the form of bug reports, pull requests or helping to diagnose bugs and help other users on the issues page.

Due to the nature of this project it can be quite time-consuming to test against real hardware, so the automated test suite is all the more important. I will not accept any pull requests that cause the build to fail, and probably will not accept any that do not have corresponding test coverage.

You can run the tests with npm:

npm test

and create a coverage report with:

npm run coverage

There is also an integration test that you can run on Raspberry Pi hardware, having connected two GPIO pins across a resistor. The command to run the test will provide further instructions on how to set up the hardware:

npm run int

The tests use mochajs as the test framework, and Sinon.JS to stub and mock out file system calls.