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Topic: Using 2 Microcontrollers powered separately  (Read 365 times) previous topic - next topic


Oct 26, 2019, 05:30 am Last Edit: Oct 26, 2019, 05:37 am by SteveMann
put a resistor between the conflicting pins - to limit the current.
it's the current that kills a pin.
I have to disagree.  You can safely connect IO1 to IO2 and set IO1 as input and IO2 as output.  You cannot hurt the input pin this way because according to the Atmega datasheet, the Arduino pins consume pretty close to zero input current.  From section 26.2 DC Characteristics:
Code: [Select]
Input Leakage Current I/O Pin low = 1 uA
Input Leakage Current I/O Pin high = 1 uA

Current doesn't kill the input pin.  It will draw only the current it needs.  But trying to suck more than 20mA from an output pin can kill it.  (Like driving a motor or solenoid directly from the I/O pin, or accidentally connecting it to ground.).

I am usually so far out of the box that most people don't know what I am talking about.

Please do not ask for help by PM. I will not respond.
If you need help, post a question on the appropriate forum.
Click on Add Karma if I helped you.


The resistor is a good idea in any situation where the pin states could become unknown !
Connecting inputs together won't cause a problem, but if you accidentally tie an output to any driven pin or supply rail is fairly certain to cause problems over time.

Do whatever you want, it's your money!
Experienced responders have a nose for laziness, (they were beginners once)... Sure, there are trolls, chest-beaters, and pretenders - but the help you'll get here is about as good as it gets - if you try to help youself!.


You can safely connect IO1 to IO2 and set IO1 as input and IO2 as output.
Nobody ever said you could not do that.


Oct 26, 2019, 08:35 am Last Edit: Oct 26, 2019, 08:48 am by Grumpy_Mike
I'm going to go out on a limb and say you didn't even read my post where I mentioned all of this including the 3.3v system in it. I'm going to also go out on a limb and say you saw images, you skipped reading, you commented on the images alone.
Well again you would be wrong. I did read everything you wrote several times before I posted. The bit where you said about using 3V3 did not make any sense in the context of the questions you were asking, so I assumed you had made a mistake because your images contradicted the words. Images are much more powerful than two words that seem to contradict them. Your questions showed you did not know very much so I assumed your words were a miss understanding of what you were dealing with. I never dreamed for a moment you would use the wrong processor in an image.

many of the information given has been downright wrong to begin with
I find that hard to believe please post a link to information you have received here that has been downright wrong and another member has not corrected it.

I did not mock you, if you think I did then this is all in your head and you should not be so paranoid.

You have to remember you are talking to engineers here, not some school teacher that has to say your opinions are valid even though they are not.

consider this thread abandoned and I'll just be posting to StackExchange from now on, at least their a lot less toxic than this dumb place.
At least we don't block posts because someone asked the same question two years ago. Good luck with that forum.

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