Always returning 1 as new value during toggling

[roccomuso]

Someone can explain why it returns always 'off' in stato? It can't toogle.

var Gpio = require("onoff").Gpio;
led = new Gpio(17, 'out');

   led.read(function (err, value) { // Asynchronous read.
        if (err) throw err;

        led.write(value ^ 1, function (err) { // Asynchronous write.
          if (err) throw err;
          var stato = (value == 1) ? "on": "off"; 
          console.log('Pin new value: '+stato);
        });
  });

For example, when i turn on the pin with a write method, everything seems to work fine, but when i try to read the pin status, the pin turn OFF and the value printed on the console is 0/off.

The weird thing is that it happens even with the rpi-gpio.js library: JamesBarwell/rpi-gpio.js#24

[fivdi]

Is it because stato is being logged to the console instead of value?

[roccomuso]

No it's just a typo in the question. Fixed.

PS. I'm using Raspbian on a Raspberry Pi B.

[fivdi]

I would expect stato to have a value of off in the example program, so everything appears to be function correctly.

This line of code creates a new Gpio object called led with an initial value of 0:

led = new Gpio(17, 'out');

This line of code reads the value of led and sets value to 0:

led.read(function (err, value) { // Asynchronous read.

This line of code therefore sets stato to off

var stato = (value == 1) ? "on": "off";

What makes you think salto should be equal to on?

PS. Please don't modify previous posts as it makes it difficult/impossible to understand the topic later.

[roccomuso]

So how can i read the value of led without setting it to 0?

Doesn't exist a way to read the pin state?

And for example how would you implement a toggling function without reading
the current pin value?

[fivdi]

There appears to be a misunderstanding here. Reading the value of a Gpio object for a LED will _NOT_ set it's value to 0. What will set it's value to 0 is creating a new Gpio object for the LED. If the program is continuously creating Gpio objects for the LED, then the value will continuously be set to 0. This should be avoided.

Please try the following program and let us know if it functions correctly. It toggles the state of a LED on GPIO 17 every 200ms, 25 times:

var Gpio = require('onoff').Gpio,
  led = new Gpio(17, 'out');

(function blink(count) {
  if (count <= 0) {
    return led.unexport();
  }

  led.read(function (err, value) {
    led.write(value ^ 1, function (err) {
    });
  });

  setTimeout(function () {
    blink(count - 1);
  }, 200);
}(25));

[roccomuso]

As you suggested, every new Gpio object sets the value to 0. Thanks, now all works fine ;)

[fivdi]

That's good news :)