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  1. #1
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    barry's Avatar
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    Midi current requirement

    I don't actually have the MIDI spec, but I've seen two different implementations supposedly excerpted from the spec, both using 5 volts: one has a 220 ohm resistor in series with the driver, the other uses TWO 220 ohm resistors, one on each leg. So assuming worst case and using the MIDI Spec specified 6N136 (with a forward voltage drop of 1.75V,) the current would be (5-1.75)/440=7mA. But the 6N136 only needs 1.6mA, according to its spec.

    I am designing a system that would run off of 3V. Is it safe to design this to provide 1.6mA, rather than 7mA? Or, more to the point, does MIDI have an actual minimum current spec?

    Thanks.

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  2. #2
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    Re: Midi current requirement

    MIDI is defined as a nominally a 5mA current loop, so I probably would not design for less then that, but I dont know what the spec actually says for minimum current.

    You want to allow for the midi input having some series resistance and maybe a transorb or something to protect the opto coupler, so 7mA into a naked 136 is probably a sane operating point.

    Regards, Dan.



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