retesting gpio with node.js and onoff with the raspberry pi 3

This is the Cylon test I created for my original personal Raspberry Pi work over two years ago (see testing gpio with node.js and onoff, February 2014) except this time I executed it on the Raspberry Pi 3, not the original Raspberry Pi. In order to make clear what I did to run this from the RPi3 side, here’s what I installed on Arch Linux via pacman:

  • gcc
  • make
  • nodejs
  • npm

I was happy to see that the Arch Linux ARM repositories carried the latest node.js and npm, versions 5.8.0 and 3.8.1 respectively. I used npm to install a local copy of onoff. I needed gcc and make because npm builds part of onoff locally during installation.

This test actually uses the code I posted (and am reposting) back in March 2014. I’m going to use the i2c and port expanders for key input. But for testing the output I use the following simple code:

// cylon.js - JavaScript application to flash four LEDs in
// a 'cylon' like fashion from side to side.
// Requires node.js and onoff

var Gpio = require('onoff').Gpio,   // Instantiate the onoff.Gpio instance.
    led1 = new Gpio(17, 'out'),     // Export GPIO pin #17 as output.
    led2 = new Gpio(18, 'out'),     // Export GPIO pin #18 as output.
    led3 = new Gpio(27, 'out'),     // Export GPIO pin #27 as output.
    led4 = new Gpio(22, 'out'),     // Export GPIO pin #22 as output.
    iv1,                            // Function to be called periodically.
    shifter = 1,                    // Bit to shift back and forth.
    multiplier = 2;                 // Determines shift direction.

// This sets up the periodically called function.
// Function is called every 50 milliseconds (see end of setInterval(...)
// A single bit is shifted low to high, then high to low, and used via
// and AND mask, to either turn the LED on (bit is '1') or turn the LED
// off (bit is '0'). This single bit, moving back and forth across four
// bits, is used to turn on a single LED, giving the illusion of the LED
// moving back and forth, like the Cylon head visor in the original
// Battlestar Galactica series (which I personally found more enjoyable
// than the reboot).

iv1 = setInterval(function() {
    led1.writeSync(shifter & 1 ? 1 : 0); // 1 = on, 0 = off
    led2.writeSync(shifter & 2 ? 1 : 0);
    led3.writeSync(shifter & 4 ? 1 : 0);
    led4.writeSync(shifter & 8 ? 1 : 0);
    shifter *= multiplier;
    if (shifter > 4) multiplier = .5;
    if (shifter < 2) multiplier = 2;
}, 50);

// Stop blinking the LEDs and turn them off after 10 seconds.

setTimeout(function() {
    clearInterval(iv1); // Stop blinking
    led1.writeSync(0);  // Turn LED off.
    led1.unexport();    // Unexport GPIO and free resources
    led2.writeSync(0);  // Turn LED off.
    led2.unexport();    // Unexport GPIO and free resources
    led3.writeSync(0);  // Turn LED off.
    led3.unexport();    // Unexport GPIO and free resources
    led4.writeSync(0);  // Turn LED off.
    led4.unexport();    // Unexport GPIO and free resources
}, 10000);

With node.js and onoff installed type ‘sudo node cylon.js‘ at the prompt to execute.

The reason I’ve gone back to node.js is because the split that occurred nearly two years ago has been healed between the Node group and io.js, the fork. Things are back to a better state.

The video at the top was created using an Olympus E-M5 Elite and an M.Zuiko 12-40mm PRO zoom in manual focus mode, zoomed out to 40mm. The manual focus eliminates the constant and annoying in-and-out automatic refocusing of the first video I took of the Cylon lighting effect. The output was edited with iMovie on my iPad Air 2. Get used to the trippy little background music, as I’ll be using it on other similar technical videos in the future.

This post concludes my breaking-in of the new Raspberry Pi 3. It also is the start of a small break in RPi3 related work as I start heading back to my regular job. The next posts will be a bit more sophisticated and unique from any prior work.

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