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hi , im new to arduino , i want to know , is it possible to make a digital I/O to consider as HIGH with 4,5 Volt ?? if its possible how to do it ?? im using Mega 2560 Thanks

NOTE: THE APPROACH THAT WAS HERE IS INCORRECT DUE TO WRONG ASSUMPTIONS. See later posts.

Removed to prevent confusion.

stevenerika:
hi , im new to arduino , i want to know , is it possible to make a digital I/O to consider as HIGH with 4,5 Volt ?? if its possible how to do it ?? im using Mega 2560 Thanks

I don't understand the question. 4.5V is considered HIGH by a 2560 processor if it's powered with 5V and the 2560 will output (close to) Vcc for a HIGH.

DaleScott:
One way (but kind of undesirable) is to connect through a resistor circuit that drops the 4.5 volts down to 2.0 volts (standard TTL minimum high level).

I don't understand the answer either. Where does that 2V come from? Where does TTL come from?

The TTL level was coming from

Does Arduino use CMOS technology? If so, the 2v value is wrong.

I took the posted question literally and was trying to give them an answer. I should have asked more questions like you did before offering a solution.

Indeed, now I'm thinking they should just put the signal in the analog input (adding a resistor for protection) and set a threshold on the ADC output digital value.

I will change my previous post to note that it is not valid.

Yes, levels are cmos.

stevenerika:
hi , im new to arduino , i want to know , is it possible to make a digital I/O to consider as HIGH with 4,5 Volt ?? if its possible how to do it ?? im using Mega 2560 Thanks

That what happens already.

I will take a punt at guessing your problem.

You do not see this as a HIGH because you have not connected the ground wire from where ever this voltage comes from to the ground connector on your Arduino.