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Topic: Uno's analog pins and short circuits (Read 1 time) previous topic - next topic

Elektromag

Hi all, this is my first post so I apologize if this is the wrong topic.  I have recently started doing the tutorial projects in the arduino starter projects. I was doing the electric keyboard and noticed something strange. It seems that when none of the keys are pressed, there is negligible resistance between the 5V pin and the A0 pin. Despite this, nothing exploded or short-circuited when I built it, and the keyboard worked as expected. Do the analog pins on the uno (and for that matter other boards) have some sort of built-in resistance? Or am I just misreading the circuit?

Thanks in advance.

fungus

When pins are set as INPUT they have a very high resistance (megaohms).
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)


DVDdoug

#3
Apr 14, 2014, 09:51 pm Last Edit: Apr 14, 2014, 09:56 pm by DVDdoug Reason: 1
It's generally OK to "short" input pins because they are simply "reading" or "sensing" a voltage.   As long as you don't connect an input pin to a negative voltage, or a voltage greater than 5V, you are safe.    You can safely connect two inputs together, although you shouldn't have a need for that very often.

However, you should never short outputs.  For example if you connect (short) an output pin to ground, you'll get excessive current and possible damage when software tries to make the output pin go high.   Or, vice-versa if you connect an output pin to +5V (or any fixed voltage).   Or if you connect two outputs together,  one output may be trying to go high while the other is trying to go low, they will "fight" and again excessive current and potential damage.

The above is true for both analog and digital inputs/outputs.      The question comes-up in audio once in awhile.... It's OK to connect the inputs of two amplifiers together to run two amplifiers from one CD player, but it's NOT OK to connect the outputs of two CD players together to run two CD players into one amplifier  (for that you need an audio mixer).

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