It is obvious, that 3,3 V is a **HIGH**, and 0 V is a **LOW** at a GPIO input pin. But I am looking for the exact voltage thresholds for the GPIO input pins. I have a `Pi B+` and a `Pi 2`.

Watching [this video](https://www.youtube.com/watch?v=Wr49ia3oID4) (for an older Pi) I get:

* **LOW: 0 - 1.19 V**
* **HIGH: 1.34 - 3.30 V**

Based on this, I connected 1 V to the GPIO input. The GPIO was still a **HIGH**. 

[This artice](http://de.scribd.com/doc/101830961/GPIO-Pads-Control2) ([linked here](https://www.raspberrypi.org/forums/viewtopic.php?f=44&t=55039)) sais:

* VIL=0.8V means that if the output is **Low** it will be **<= 0.8V**.
* VIL=1.3V means that if the output is **High** it will be **>= 1.3V**

These values are coming from the BCM2835, which the [Pi until B+ is having](https://en.wikipedia.org/wiki/Raspberry_Pi#Specifications).

I continued reading [this article](http://www.mosaic-industries.com/embedded-systems/microcontroller-projects/raspberry-pi/gpio-pin-electrical-specifications#input-and-output-pin-electrical-specifications):

* *"Normally the voltage threshold is about 1.8V, but it isn't guaranteed; it can be anywhere between the maximum input **low** and minimum input **high**, that is, between about **0.8 and 2.0V**."*

These values are coming from the ARM1176JZF, which the [Pi until B+ is having](https://en.wikipedia.org/wiki/Raspberry_Pi#Specifications). 

Looking at [the table](http://www.mosaic-industries.com/embedded-systems/microcontroller-projects/raspberry-pi/gpio-pin-electrical-specifications#input-and-output-pin-electrical-specifications), I get:

* Input **high** voltage VIH **> 2.00 V**
* Input **low** voltage VIL **< 0.80 V**

So: what are the real thresholds? Are they coming from the BCM2835 or the ARM1176JZF? How about the Pi 2? Are the thresholds still the same as for the Pi B+?

EDIT: [This article](http://elinux.org/RPi_GPIO_Interface_Circuits) sais, "*The GPIO pins are connected directly to the BCM2835 chip at the heart of the Raspberry Pi*". Because of this I guess, the values are coming from the BCM2835 and they are 0,8 V and 2 V.

EDIT2: I using wiringPI with the following code to read the LOW/HIGH value:

```
gpio -g mode 21 in
gpio -g read 21

```