newbie: use digital i/o pin as input for this situation?

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i want "monitor" circuit + , gnd of led terminal.  basically, when led on (or flashed - same thing), want detect that.

question is: need measure on circuit make safe plug 1 of arduino [uno] digital i/o pins?

for example, need check voltage coming thru connectors , make sure it's within tolerance?  should use resistor of kind "pull down" circuit when it's not (supposed be) lighting led?

basically, i'm pretty programming (including c/c++), , know bit electricity -- electronics newbie.

thanks in advance,
aj

quote
basically, i'm pretty programming (including c/c++), , know bit electricity -- electronics newbie.


as understand programming why need read value of output pin when it's software commands turn led on in first place. use flag variable , set true anytime set output pin true , set flag false anytime set output pin false. in code anytime need know state of output pin read flag variable.

don't make task more complicated needs be.

lefty


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