rx-gpio.js

Watch GPIO pins with rxjs / node.js. Provides streams for PWM data as well.

Setup

This module can then be installed with npm:

$ npm install rx-gpio

Dependencies

This modules leverages onoff to access the GPIO port. In particular, the same numbering (BCM) as onoff needs to be used.

Usage

• Capture PWM data from PPD42 dust sensor

import RxRpi from 'rx-gpio';

let gpio = 4, sampling_time = 30000;

let disp = RxRpi.pulseInLow(gpio, sampling_time)
  .map((lpo) => ({
    lpo: lpo.toFixed(2),
    concentration: Math.round(1.1*Math.pow(lpo,3)-3.8*Math.pow(lpo,2)+520*lpo+0.62)
  })
  .subscribe((x) => {
    console.log(`Low Pulse Occupancy = ${x.lpo}% / PM1 concentration = ${x.concentration} pcs/0.01cf`)
  });
  
// Disposing the subscription will cancel the watch and unexport the pin: 
// disp.dispose();

API

/**
 * sets the given channel to the provided direction/edge, and reports any change to the returned observable<0|1>
 */
function watch(channel: int, direction: string, edge: string) { ... }

/**
 * sets the giving channel to input and edge detection, and reports the (low) PWM ratio over
 * (at least) the provided period. Based solely on GPIO interrupts (no timer), hence may not
 * behave adequately for signals with a frequency below the sampling time.
 * 
 * @returns an observable<ratio: float>, representing the time ratio (0-100) for which the signal was low
 */
function pulseInLow(channel, sampletime_ms) { ... }

/**
 * sets the giving channel to input and edge detection, and reports the (high) PWM ratio over
 * (at least) the provided period. Based solely on GPIO interrupts (no timer), hence may not
 * behave adequately for signals with a frequency below the sampling time.
 * 
 * @returns an observable<ratio: float>, representing the time ratio (0-100) for which the signal was high
 */
function pulseInHigh(channel, sampletime_ms) { ... }

License

TODO