Catch Low level on INT0

[alexblade]

Sorry for noob question
I have some external line (pin) where usually high level (2.8V) on it and some times low level (20ms)
how connect -
is it enough connect this external pin direct to D2 (Nano board) without resistor (pullup/pulldown/etc) ? pls find attach

and how setup pin and interrupt to catch low level

pinMode(2, INPUT); 
//or
pinMode(2, INPUT_PULLUP);
//and
attachInterrupt(0, blink, CHANGE);
//or
attachInterrupt(0, blink, LOW;
//or
attachInterrupt(0, blink, FALLING );

[anon73444976]

Never use LOW - the interrupt will trigger as long as the condition persists.

I'd use FALLING.

[jremington]

Please describe the device that is providing the "external signal".

It is not safe to connect powered external equipment to an input on an unpowered Arduino, without using a series resistor (typically 10K).

[alexblade]

A or B ? and HIGH as I mentioned is 2.8V
device is gsm modem

[alexblade]

ok, but how setup

pinMode(2, INPUT); 
//or
pinMode(2, INPUT_PULLUP);

[groundFungus]

A) to protect the input.

For a 5V Nano, 2.8V is not a HIGH. A high (Vih) for a 5V ATmega328 chip is 0.6 * Vcc = 0.6 * 5V = 3.0V. See page 258 of the data sheet.

[jremington]

Option A is "a series resistor" but it should be 10K. And do take note of @groundFungus comment.

You need a level shifter for a 2.8V signal, or use a 3.3V Arduino.

[GolamMostafa]

@anon73444976

Never use LOW - the interrupt will trigger as long as the condition persists.

But the option is there (Fig-1):

Figure-1:

[anon73444976]

@GolamMostafa

But the option is there

So use it.
Enjoy.

(Did you imagine I didn't know it was an option?)

[GolamMostafa]

@anon73444976

(Did you imagine I didn't know it was an option?)

You might have a good reason to discourage the use of this (AL) option.

[anon73444976]

AL?
What's that?

Some esoteric jargon?

[GolamMostafa]

@anon73444976

AL?
What's that?

Left-top of Fig-1 of Post-8.

[anon73444976]

@GolamMostafa

Left-top of Fig-1 of Post-8.

Yes, but what is it?
I can't find that figure in the processor datasheet - where did it come from?
What does "AL" mean, in terms a person familiar with the processor family would understand?

(Esoteric jargon?)

[GolamMostafa]

@anon73444976

Yes, but what is it?

At the left-top of Fig-1 of Post-8, there are other acronymes like FE, RE, and AH; but, why have you been particulalry interested for AL? It is for Awami League - the Ruling Party of Bangladesh. Do you believe?

[anon73444976]

@GolamMostafa

Do you believe?

Do you understand "esoteric"?

@GolamMostafa

why have you been particulalry interested for AL?

Because it was the one you quoted.

Welcome to my mute list.

[alexblade]

I have tried on 5v micro board (I think on Nano will be the same)

@alexblade

pinMode(2, INPUT_PULLUP);
//and
attachInterrupt(0, blink, FALLING );

with direct connect w/o resistor and I catch it (low level) successfully