gpio

gpio - talk to your Single Board Computer's gpio headers

Introduction

This plain JavaScript module is generic and only rely on system's sysfs.

Please consider other (more mature) gpio libraries out there which support better your hardware,

For instance, of you're looking for a reliable way to communicate with the Raspberry Pi using JavaScript, check out the wiring-pi JavaScript library. It provides direct bindings to the fully-featured Wiring Pi C library.

But if you want/need a generic lightweight module, this one can be used as fallback.

Support

Following hardware was reported to work (with some limitations or workarounds)

• ARTIK10 (inputs' pull down resistors are enabled by default)
• Raspberry Pi (use wiringpi's /usr/bin/gpio to change mode: gpio -g mode 11 up)

Installation

Get node.js for your SBC, If using Debian or deviates (Raspbian for RPi), you can simply run: sudo apt-get install nodejs

otherwise, install from node or compile it

Usage

This library is an npm package, just define "gpio" in your package.json dependencies or

npm install gpio

Note: you must be have proper privileges to access the GPIO headers (or run node as root).

Standard setup

var gpio = require("gpio");
 
// Calling export with a pin number will export that header and return a gpio header instance
var gpio4 = gpio.export(4, {
   // When you export a pin, the default direction is out. This allows you to set
   // the pin value to either LOW or HIGH (3.3V) from your program.
   direction: gpio.DIRECTION.OUT,
 
   // set the time interval (ms) between each read when watching for value changes
   // note: this is default to 100, setting value too low will cause high CPU usage
   interval: 200,
 
   // Due to the asynchronous nature of exporting a header, you may not be able to
   // read or write to the header right away. Place your logic in this ready
   // function to guarantee everything will get fired properly
   ready: function() {
   }
});

Header direction IN

If you plan to set the header voltage externally, use direction in and read value from your program.

var gpio = require("gpio");
var gpio4 = gpio.export(4, {
   direction: gpio.DIRECTION.IN,
   ready: function() {
   }
});

API Methods

// sets pin to high
gpio4.set();

// sets pin to low (can also call gpio4.reset())
gpio4.set(0);

// Since setting a value happens asynchronously, this method also takes a
// callback argument which will get fired after the value is set
gpio4.set(function() {
   console.log(gpio4.value);    // should log 1
});
gpio4.set(0, function() {
   console.log(gpio4.value);    // should log 0
});

// unexport program when done
gpio4.unexport();

EventEmitter

This library uses node's EventEmitter which allows you to watch for value changes and fire a callback.

// bind to the "change" event
gpio4.on("change", function(val) {
   // value will report either 1 or 0 (number) when the value changes
   console.log(val)
});
      
// you can bind multiple events
var processPin4 = function(val) { console.log(val); };
gpio4.on("change", processPin4);
            
// unbind a particular callback from the "change" event
gpio4.removeListener("change", processPin4);
      
// unbind all callbacks from the "change" event
gpio4.removeAllListeners("change");
      
// you can also manually change the direction anytime after instantiation            
gpio4.setDirection(gpio.DIRECTION.OUT);
gpio4.setDirection(gpio.DIRECTION.IN);

Example

Cycle voltage every half a second

var gpio = require("gpio");
var gpio22, gpio4, intervalTimer;
 
// Flashing lights if LED connected to GPIO22
gpio22 = gpio.export(22, {
   ready: function() {
      intervalTimer = setInterval(function() {
         gpio22.set();
         setTimeout(function() { gpio22.reset(); }, 500);
      }, 1000);
   }
});
 
// Lets assume a different LED is hooked up to pin 4, the following code 
// will make that LED blink inversely with LED from pin 22 
gpio4 = gpio.export(4, {
   ready: function() {
      // bind to gpio22's change event
      gpio22.on("change", function(val) {
         gpio4.set(1 - val); // set gpio4 to the opposite value
      });
   }
});
 
// reset the headers and unexport after 10 seconds
setTimeout(function() {
   clearInterval(intervalTimer);          // stops the voltage cycling
   gpio22.removeAllListeners('change');   // unbinds change event
   gpio22.reset();                        // sets header to low
   gpio22.unexport();                     // unexport the header
   
   gpio4.reset();
   gpio4.unexport(function() {
      // unexport takes a callback which gets fired as soon as unexporting is done
      process.exit(); // exits your node program
   });
}, 10000)

References

Demos on Raspberry Pi:

• Demo using LED: http://www.youtube.com/watch?v=2Juo-CJ6eu4
• Demo using RC car: http://www.youtube.com/watch?v=klQdX8-YVaI
• Source code here: https://github.com/EnotionZ/node-rc