Catch Low level on INT0

Projects Programming
1

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
external

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 );
2

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

I'd use FALLING.

3

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).

4

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

5

ok, but how setup

pinMode(2, INPUT); 
//or
pinMode(2, INPUT_PULLUP);
6

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.

7

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.

8

But the option is there (Fig-1):

intUnd
intUnd877×263 26.4 KB

Figure-1:

9

So use it.
Enjoy.

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

10

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

11

AL?
What's that?

Some esoteric jargon?

12

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

13

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?)

14

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?

15

Do you understand "esoteric"?

Because it was the one you quoted.

Welcome to my mute list.

17

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

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

18

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