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### Topic: Voltage input on digital pin (Arduino Uno) (Read 2750 times)previous topic - next topic

#### Tortun

##### May 12, 2012, 08:53 pm
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

#### Runaway Pancake

#1
##### May 12, 2012, 09:39 pm

... 0,5 volt. Will the digital input pin register that?

As a LOW, yes.
I wouldn't expect anything < 3V to be a consistently reliable "HIGH".
"You gotta fight - for your right - to party!"
"Who is like unto the beast? who is able to make war with him?"
It's "bipolar transistor" or "junction transistor" - "BJT" is stupid.
When all else fails, check your wiring!

#### Tortun

#2
##### May 12, 2012, 09:51 pm
So if I go below 3V on a digital pin, the Arduino Uno would not register it as HIGH.
Thank you

#### retrolefty

#3
##### May 12, 2012, 09:51 pm

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

#### Runaway Pancake

#4
##### May 12, 2012, 10:01 pm

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

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.
"You gotta fight - for your right - to party!"
"Who is like unto the beast? who is able to make war with him?"
It's "bipolar transistor" or "junction transistor" - "BJT" is stupid.
When all else fails, check your wiring!

#### Tortun

#5
##### May 12, 2012, 11:01 pm

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  :~

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.

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

#### AWOL

#6
##### May 12, 2012, 11:18 pm
Quote
Unfortunately, that didn't help me

It's all there in the data sheet.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

#### Grumpy_Mike

#7
##### May 12, 2012, 11:35 pm
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

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