Issues converting Python script to Node.js

Question

UPDATE: rewritten code but still not working

The new code below is still copying the functionality of the python script, however trying to simplify things (also using a different library https://npmjs.org/package/rpi-gpio ) The problem now is that is always get a similar read back, so it is obviously not using the feedback from the GPIO pins.

var gpio = require('rpi-gpio');

var pin   = 12,
    delay = 0.0005,
    startTime,
    endTime,
    duration,
    distance;

function on(){
    setTimeout(gpio.write(pin,1,off),delay);
}

function off(){
    setTimeout(gpio.write(pin,0,listen),delay);
}

function listen(){
    gpio.setup(pin, gpio.DIR_IN);
    startTime = Date.now();
    console.log('Start: ' + String(startTime));
    return;
}

gpio.on('change', function(channel, value) {
    endTime = Date.now();
    console.log('End: ' + String(endTime));
    duration = endTime - startTime;
    console.log('Duration: ' + String(duration));
    distance = ((duration / 100) * 3400) / 2;
    console.log(distance);
    return process.exit(0);
});
gpio.setup(pin, gpio.DIR_OUT, on);

---

ORIGINAL POST

I am trying to convert a working python script as a part of my RPi development project into node.js to avoid needing to use websockets.

This is the working python script:

import time
import RPi.GPIO as GPIO
import websocket

for x in range(0, 10):

    GPIO.setmode(GPIO.BOARD)
    GPIO.setup(12, GPIO.OUT)

    #cleanup output 
    GPIO.output(12, 0)

    time.sleep(0.000002)

    #send signal
    GPIO.output(12, 1)

    time.sleep(0.000005)

    GPIO.output(12, 0)

    GPIO.setup(12, GPIO.IN)

    while GPIO.input(12)==0:
            starttime=time.time()

    while GPIO.input(12)==1:
            endtime=time.time()

    duration=endtime-starttime
    distance=duration*34000/2

    print str(x + 1) + ": " + str(distance)

    time.sleep(1)

The function of this script is to use an attached proximity sensor to measure distance.

My current (messy) rewrite for node.js (using https://github.com/rakeshpai/pi-gpio for the GPIO parts):

var gpio = require("pi-gpio");

function rightPingOn() {
gpio.write(12, 1, function(err){
    //if(err) throw err;
    console.log("Sent 1");
});         // Set pin 12 high
}

function rightPingOff() {
gpio.write(12, 0, function(err){
    //if(err) throw err;
    console.log("Sent 0");
});         // Set pin 12 low
}

function setRightListen() {
gpio.setDirection(12, "input");    // Open pin 16 for input 
}

function setRightOutput(){
gpio.setDirection(12, "output");  // Open pin 12 for output
}

function right_listen(){
gpio.read(12, function(err, value){
    //if(err) throw err;
    console.log("Listened");
    return value;
});
}

gpio.open(12);
setRightOutput();
rightPingOff();
setTimeout(rightPingOn, 0.5);
setTimeout(rightPingOff, 0.5);
setRightListen();

while (right_listen == 0){
var startTime = getTime();
}

while (right_listen == 1){
var endTime = getTime();
}

gpio.close(12);

var duration = endTime - startTime;
var distance = duration * 3400 / 2

console.log(distance);

All I currently have as an output of this script is:

NaN
Sent 0
Sent 1
Sent 0

Any help would be appreciated!

Answer 1

oh man. i think you're going to have a hard time with this. I'm guessing the python GPIO interface is synchronous?

To start with, polling like this:

while (right_listen == 0){
   var startTime = getTime();
}

while (right_listen == 1){
   var endTime = getTime();
}

is likely to result in an infinite loop because the callbacks that are supposed to be changing the value of right_listen are never going to get a chance to run. If the following section is supposed to occur in a set order:

gpio.open(12);
setRightOutput();
rightPingOff();
setTimeout(rightPingOn, 0.5);
setTimeout(rightPingOff, 0.5);
setRightListen();

and those calls really are asynchronous, you are going to have to chain them together explicitly.

Edit: note this is only a guideline for how the code might end up looking.

(1) Notice I don't handle errors. (2) That deep nesting is often called 'callback hell', modules like async can make the code much nicer (3) There are likely small errors in here.

gpio.open(12, function(error) {
    gpio.setDirection(12, "output", function(error) {
        gpio.write(12, 0, function(error) {
            setTimeout( function() {
                var started = getTime();
                gpio.setDirection(12, "input", function(error, value) { 
                    console.log("received:", value, "after:", getTime()-started);
                })
            }, 500)
        })
    })
})