Pi Zero LED demo

This how-to isn't really part of the Hydra Cluster but was included in a related presentation entitled Node in small places

This how-to discusses how to use a Raspberry Pi to control an LED light. If you haven't already setup your Pi Zero, see Setting up a Pi Zero for step-by-step instructions.

The wiring is as basic as it gets. The ground has a 220 Ohm resistor leading to the LED anode terminal, and the power from pin 4 is connected to the cathode terminal.

This demo uses a node package called pi-blaster to assist in controlling an LED light state and brightness. The pi-blaster repo offers several ways to install pi-blaster, but I opted to pull the code down and build it manually, largely because at the time of this writing there was a problem using a straight NPM install.

SSH into your Raspberry Pi:

$ ssh pi@raspberrypi.local

Then...

$ sudo apt-get install git
$ sudo apt-get install autoconf
$ git clone https://github.com/sarfata/pi-blaster.git
$ cd pi-blaster
$ ./autogen.sh
$ ./configure
$ make
$ sudo make install

Next create an led-demo project folder and install the pi-blaster.js package so we can control the daemon via Node.js

$ mkdir led-demo
$ cd led-demo
$ npm init
$ npm install pi-blaster.js --save

The following sine.js program using a sine wave to change the brightness of the LED so that it pulsates based on the iterated value of points on the wave.

const piblaster = require('pi-blaster.js');
const LED_PIN = 4;

let y = 0;
let intervalID = setInterval(() => {
  let s = Math.abs(Math.sin(y/10));
  piblaster.setPwm(LED_PIN, s);
  y += 1;
  if (y > 180) {
    y = 0;
  }
}, 100);

process.on('SIGINT', () => {
  clearInterval(intervalID);
  piblaster.setPwm(LED_PIN, 0);
  setTimeout(() => {
    process.exit();
  }, 1000);
});

The following sos.js program repeats an SOS morse code destress signal:

const piblaster = require('pi-blaster.js');
const LED_PIN = 4;
const LED_ON = 1;
const LED_OFF = 0;
const SOS_PATTERN = [
  LED_ON, LED_ON, LED_ON,
  LED_OFF,
  LED_ON, LED_OFF, LED_ON, LED_OFF, LED_ON,
  LED_OFF, LED_OFF,
  LED_ON, LED_ON, LED_ON,
  LED_OFF, LED_OFF, LED_OFF, LED_OFF, LED_OFF, LED_OFF];

let i = 0;
let intervalID = setInterval(() => {
  piblaster.setPwm(LED_PIN, SOS_PATTERN[i]);

  if (i > SOS_PATTERN.length - 1) {
    i = 0;
  } else {
    i += 1;
  }
}, 500);

process.on('SIGINT', () => {
  clearInterval(intervalID);
  piblaster.setPwm(LED_PIN, 0);
  setTimeout(() => {
    process.exit();
  }, 1000);
});