midi IN automatically sends to midi OUT : what's wrong ?

Other Hardware Audio
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hello !
i've built a fairly standard ( i think ) midi IN and OUT interface for an Arduino project ;
midi OUT works fine when alone ;
midi IN works fine when OUT is not going to the same synth ;
but when i have midi IN and OUT going to the same machine, i have some kind of "feedback" : the midi IN signal goes directly to OUT and repeats the played not, even though the Arduino is not at all processing midi IN or OUT signals. I suppose something must be happening at breadboard level, but what could it be ? the midi OUT seems to be exactly the midi IN value. For instance if i use a synth as Channel 1 going to midi IN and a drum machine also set at Channel 1 attached to OUT, if i hit one key on the synth it automatically plays the same value in the drum machine ( without again the Arduino processing anything )...
what's wrong with my circuitry or understanding of midi ?

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Sylvain

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what's wrong with my circuitry or understanding of midi ?

Hard to tell when half the components can't be seen. And while you are at it how about posting the code as well.

It sounds like software, or the other end of your hardware.

If MIDI out works without an echo with nothing plugged in, it can't be the Aduino hardware can it. If that same MIDI output gets echoed back then it must be your keyboard that does the echoing.

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Have you got MIDI Through, sometimes called thru, enabled in the software?

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i'm using the FortySevenEffects MIDI library... and indeed now that i'm looking more carefully at the documentation there is a way to turn off MIDI thru : turnThruOff() - i think that must be the problem, i'll try this ! thanks !!!

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i'm using the FortySevenEffects MIDI library.

Would have been good to know this on the first post.