Midi input problem

Started by Justin July 28, 2005
Hey, I'm making a synth with a bx-35 and am using a MAX3110 as the
MIDI uart. And am using this schematic:
http://devices.sapp.org/micro/stamp2sx/max3110/bsmax3110big.gif as a
reference (but with the Basic Stamp replaced by the BX35). I've got
all the SPI communications working fine, and MIDI out works great. The
problem is that when I connect a midi controller to the MIDI input the
MAX immediatly signals data is avilable (when it's not) and returns
garbage as the input data (specifically 0x11111100 and 0x11111000) .
If I connect the MAX's RX pin directly to +5v everything is normal and
no input is ever signalled. Does anyone have any idea what's going on?

Thanks,
Justin


I've been doing some experimenting and found that when I plug the midi
output of my computer into the MAX3110 it works fine. But both my midi
controller and drum machine create the garbage pattern. Is there any
way to amplify the midi input signal before it hits the opto-isolator?

Justin

--- In basicx@basi..., "Justin" <dontbo@y...> wrote:
> Hey, I'm making a synth with a bx-35 and am using a MAX3110 as the
> MIDI uart. And am using this schematic:
> http://devices.sapp.org/micro/stamp2sx/max3110/bsmax3110big.gif as a
> reference (but with the Basic Stamp replaced by the BX35). I've got
> all the SPI communications working fine, and MIDI out works great. The
> problem is that when I connect a midi controller to the MIDI input the
> MAX immediatly signals data is avilable (when it's not) and returns
> garbage as the input data (specifically 0x11111100 and 0x11111000) .
> If I connect the MAX's RX pin directly to +5v everything is normal and
> no input is ever signalled. Does anyone have any idea what's going on?
>
> Thanks,
> Justin



> ... when I plug the midi output of my computer into the MAX3110 it
works fine...

Then it sounds like the problem is noise. MIDI cable signals are
digital current loops, something like 5mA or greater, so amplifying a
MIDI signal is unnecessary; it's either there or it's not.

Are all of your devices powered from the same strip, sharing the same
earth ground? Tom



I checked all that, and it's all good there. I was thinking about
puttin some caps inline with the midi signal coming in, do you think
that would clean the signal up at all?

--- In basicx@basi..., Tom Becker <gtbecker@r...> wrote:
> > ... when I plug the midi output of my computer into the MAX3110 it
> works fine...
>
> Then it sounds like the problem is noise. MIDI cable signals are
> digital current loops, something like 5mA or greater, so amplifying a
> MIDI signal is unnecessary; it's either there or it's not.
>
> Are all of your devices powered from the same strip, sharing the same
> earth ground? > Tom



> ... putting some caps inline with the midi signal coming in...

No, that is unlikely to work.

Perhaps you'll find an answer if you discuss this problem with other
MIDI users. Here are 885 MIDI group hits on Yahoo:
http://groups.yahoo.com/search?query=midi&submit=Search Tom