# Voltage input on digital pin (Arduino Uno)

Hello all

What is the lower limit of voltage, the Arduino Uno will register on one of the digital pins?

For example, a curcuit is connected trough Arduino 5V and GND and have a output at only 0,5 volt. Will the digital input pin register that?

Thanks

Tortun:
â€¦ 0,5 volt. Will the digital input pin register that?

As a LOW, yes.
I wouldnâ€™t expect anything < 3V to be a consistently reliable â€śHIGHâ€ť.

So if I go below 3V on a digital pin, the Arduino Uno would not register it as HIGH.
Thank you

Tortun: Hello all :)

What is the lower limit of voltage, the Arduino Uno will register on one of the digital pins?

For example, a curcuit is connected trough Arduino 5V and GND and have a output at only 0,5 volt. Will the digital input pin register that?

Thanks :)

Those values are best defined and explained in the Atmel ATmega329p datasheet along with all the other electrical specifications for the chip.

Lefty

Tortun: So if I go below 3V on a digital pin, the Arduino Uno would not register it as HIGH. Thank you :D

Well, I didn't "say" that, but you asked about "0.5V" In fact there's a point at which a voltage "must be" a HIGH and a similar point where some voltage "must be" a LOW, but there's a window of uncertainty between the two, a sort of no-man's land which should be avoided.

retrolefty: Those values are best defined and explained in the Atmel ATmega329p datasheet along with all the other electrical specifications for the chip.

Lefty

Unfortunately, that didn't help me :~

[quote author=Runaway Pancake link=topic=105590.msg792294#msg792294 date=1336852918] Well, I didn't "say" that, but you asked about "0.5V" In fact there's a point at which a voltage "must be" a HIGH and a similar point where some voltage "must be" a LOW, but there's a window of uncertainty between the two, a sort of no-man's land which should be avoided.

[/quote] What voltage is that between? The uncertainty about "HIGH" and "LOW". If you should say a voltage, were it would not anymore register a value as "HIGH" or the highest voltage you can think off, were it not at all would read it as "HIGH". (at least theoretically?) Sorry... But I really need some sort of number, since I have made an error with an operational amplifier... Hope there is some kind of possible answer :(

Unfortunately, that didn't help me

It's all there in the data sheet. In what way didn't it help you?

For an input to be seen as a logic low it must be below 0.3 * Vcc so at 5V Vcc this is below 1.5V

For an input to be seen as a logic high it must be above 0.6 * Vcc so at 5V Vcc this is above 3V