gpioUtil: A Node wrapper for Wiring Pi's gpio

gpioUtil is a Node wrapper for the Wiring Pi gpio utility, which manages the Raspberry Pi’s GPIO pins. It currently supports the core functions:

• export, unexport, unexportall,
• read, write, pwm,
• readall, exports,
• mode, edge,
• version.

(Need anything else? File an issue.)

If you’re not sure what all this is about, please read the gpio utility’s page. gpioUtil is really just a very thin wrapper that allows comfortable invocation from a Node program. Here’s the most important bit:

gpio can control, read and write the GPIO pins, and export/unexport pins via the /sys/class/gpio interface, where they will then be available to user programs (without requiring root privileges).

gpio and gpioUtil are by nature not suited for very frequent read/writes (say, more than one call per minute).
(If that’s what you need, try [wiring-pi][wpi-node-addon], which has Node bindings to the native Wiring Pi library. [In my experience][piswitch], it’s fast enough for sub-millisecond precision.)

[wpi-node-addon]: https://github.com/eugeneware/wiring-pi) [piswitch]: https://github.com/tjanson/PiSwitch

Wiring Pi Installation

If you haven’t already, please install Wiring Pi, which includes the gpio utility, [as described on their website][wpi-install]. [wpi-install]: http://wiringpi.com/download-and-install/

Usage

Here’s a simple example of how gpioUtil might be used:

var gpioUtil = require('pi-gpioutil');
var pinBcm = 17; // BCM numbering
var pinWiring = 0; // Wiring Pi numbering (yes, this is confusing)
gpioUtil.export(pinBcm, 'in', function(err) {
  if (!err) {
    gpioUtil.read(pinWiring, function(err, stdout, stderr, value) {
      if (value) console.log('Input is HIGH!');
    });
  }
});

Reference

General information

All functions have the general form fct([[pin, [params]], [callback]), and do the following:

1. the input parameters are checked for (syntactic) validity
2. the gpio utility is called via child_process.exec()
3. the exec()s err, stdout, stderr are passed to the callback (i.e., you may inspect the raw output)
4. if the call is meant to return data, the utility’s output is converted for easier processing and passed as a fourth parameter (e.g., readall provides a JSON representation of all pins)

Pin numbers are passed untouched, which means that the Broadcom numbers are used for [un]export, while the Wiring Pi numbering scheme is used for everything else. Neither of course matches the physical pin layout.
Confused? So in everyone else, but there’s this really pretty pinout reference by Philip Howard to make up for it.

When reading pins, high and low voltages are converted to the boolean true/false, respectively.

Important functions

Once again, please refer to the gpio utility’s page for details of what a function does; the following will tell you how to call it.
Callback will always be passed err, stdout, stderr as the first three arguments.
Pin numbers are in Wiring Pi format if not noted otherwise.

• export(pin, direction, callback): pin in BCM numbering, direction: 'in' or 'out'
• unexport(pin, callback): pin in BCM numbering
• read(pin, callback): fourth argument to callback: boolean, true for high voltage, false for low
• write(pin, value, callback: value: true/false (or 1/0) for high/low respectively
• readall(callback): fourth argument to callback: JSON representation of all pins and their states
• exports(callback): fourth argument to callback: JSON representation of exported pins
• version(callback): fourth argument to callback: version string (e.g., '2.13')