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I am trying to control a raspberry pi through web socket. I found a similar project and have been building my project around it. I have managed to get everything except a distance sensor working.

tank.getDistance = function () {
   async.parallel([
    gpio.write(trig,0),
    gpio.write(trig,1),
    gpio.write(trig,0),
  ]);
  var start,stop;
  while(gpio.read(echo) == 0){start = Date.now();}
  while(gpio.read(echo) == 1){stop = Date.now();}
  var distance = ((stop-start)/1000.0)*17000
  console.log("distance: "+ distance);
};

this is how i am trying to read from the ultrasonic sensor. I have tested this logic in python and it was working there.

socket.on('keydown', function (dir) {
    switch (dir) {
      case 'up':
        tank.moveForward();
        console.log("forward");
        tank.getDistance();
        break;
...

this is where i call the function. But every time I call this function, I get a 

/home/pi/marinaBot/marinaBot/node_modules/rpi-gpio/rpi-gpio.js:286
            throw new Error('A callback must be provided')
            ^
Error: A callback must be provided
    at Gpio.read.input (/home/pi/marinaBot/marinaBot/node_modules/rpi-gpio/rpi-gpio.js:286:19)
    at Object.tank.getDistance (/home/pi/marinaBot/marinaBot/app.js:78:14)

not sure why this is occurring as I am not returning anything. I have tried using other ultrasonic libraries like "r-pi-usonic" but I dont understand the setup of it. Any Ideas? Just starting to learn NodeJS. this may be something realluy simple.

Wang Liang
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sakib11
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    async.parallel(items, cb) - expects you to send a callback as the second parameter, also all the logic should be done there, or if you don't like callback approach you can switch to Promises it is cleaner in the end – Alexandru Olaru May 01 '19 at 11:06

1 Answers1

1
gpio.read(echo, callbackfunction(error, data){})

Please check this document

https://github.com/JamesBarwell/rpi-gpio.js#readchannel-callback

You need async/await function for while 

var gpio = require('rpi-gpio')

var gpio_read = function (channel) {
    return new Promise(resolve => {
        gpio.read(channel, function (error, result) {
            console.log('gpio.read', error, result);
            resolve(result);
        });
    });
}

var echo = 16;

var calculateDistance = async function () {
    var start, stop;

    while (await gpio_read(echo) == false) { start = Date.now(); }
    while (await gpio_read(echo) == true) { stop = Date.now(); }
    var distance = ((stop - start) / 1000.0) * 17000
    console.log("distance: " + distance);
}

gpiop.setup(echo, gpio.DIR_IN)
    .then(function () {
        calculateDistance();
    })
    .catch((err) => {
        console.log('Error: ', err.toString())
    })

Updated content:
1. Created calculateDistance function with async as 

  var calculateDistance = async function () { ... }
  1. return new Promise
Wang Liang
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