I/O input pins voltage 5V

[seppo]

Hello!

I have a external device (communicating with TTL level signals) which is working well with Arduino Mega 2560 R3 through digital IO pins of Mega,
now if I try out Arduino Due with this device which writes 4, 82 volts (measured from pin) to Arduino input pin, is there a risk of damage ,
does anybody know the input circuit diagram of Due digital inputs ?
in my case , the output from Due is ok since the device accepts also lower voltages (3,3 V),

lowering the voltage with resistance divider is of course one solution but if inputs work with 4,8 V , it saves some extra work,

BR,
Seppo 

[Tom Carpenter]

The inputs of the Due are NOT 5v tollerant. If you try and apply a 5v signal (that includes 4.8v), you will damage the arm processor.

[seppo]

hello!

thank you for swift and clear answer,
I will make the voltage drop from TTL to 3,3 V using resistors,

BR,

Seppo

[graynomad]

From the Due product page

Warning: Unlike other Arduino boards, the Arduino Due board runs at 3.3V. The maximum voltage that the I/O pins can tolerate is 3.3V. Providing higher voltages, like 5V to an I/O pin could damage the board.

_____
Rob

[Markus_L811]

From the Due product page

Warning: Unlike other Arduino boards, the Arduino Due board runs at 3.3V. The maximum voltage that the I/O pins can tolerate is 3.3V. Providing higher voltages, like 5V to an I/O pin could damage the board.

_____
Rob

Maybe it would be better that the Due-Board doesn't have an 5V Pin on it so it's clear that the SAM3X8E isn't for 5V and nobody makes a mistake and jumpered 5V to some I/O Pin.

[graynomad]

Not a bad idea although there are valid reasons for needing 5v even on a Due-compatible shield that is otherwise 3v3.

Maybe the 5v socket hole should be plugged (I think you can get plugs used for keying sockets) so that normally a 5v shield can't be plugged in, but if you happen to have a compatible shield that still needs 5v you can remove the plug.

______
Rob

[Patouf]

Hi , i'm new with arduino but i saw that the newest versionf of the shields have an IOref pin, so maybe they can adapt to the due...

[graynomad]

Yep, that's the reason for IOREF, trouble is that's a new signal and all the old shields don't have it.

So there is some potential for an old shield to put 5v onto a Due 3v3 pin.

FWIW I'm suggesting that the Due have the 5v hole plugged so an old shield (or indeed any shield that can cause 5v damage) cannot even be plugged in by a beginner.

A new 3v3 shield that doesn't need 5v wouldn't have the pin, so it will plug in.

Any shield that does need the 5v can still be plugged in if you remove the keying plug from the socket. One would assume that anybody doing this is working under instructions or knows what they are doing.

Any Arduino team reading this? Is this a reasonable idea or a waste of time

_____
Rob