rpi-gpio

rpi-gpio.js

Control Raspberry Pi GPIO pins with node.js

Setup

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

This module can be installed with npm:

npm install rpi-gpio

Usage

Please see the examples below. Make make sure you are running as root or with sudo, else the Raspberry Pi will not let you output to the GPIO. All of the functions relating to the pins within this module are asynchronous, so where necessary - for example in reading the value of a pin - a callback must be provided.

Please note that there are two different ways to reference a channel; either using the Raspberry Pi or the BCM/SoC naming schema (sadly, neither of which match the physical pins!). This module supports both schemas, with Raspberry Pi being the default. Please see this page for more details.

Query the value of a pin

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

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

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

Listen for changes on a pin

The GPIO module inherits from EventEmitter so any of the EventEmitter functions can be used. The example below shows how to listen for a change in value to a channel.

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);

Write to a pin

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

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

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

Unexport pins when finished

This will close any pins that were opened by the module.

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');
        return process.exit(0);
    });
}

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,
    delay = 2000,
    count = 0,
    max   = 3;

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

function on() {
    if (count >= max) {
        gpio.destroy(function() {
            console.log('Closed pins, now exit');
            return process.exit(0);
        });
        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');

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

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');
                return process.exit(0);
            });
        }, 500);
    });
};

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