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PICList Thread
'MIDI from PIC devices'
1997\12\08@151927 by Bob Shaver

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This message forwarded to the PIC group with permission of the sender.  My reply to the original newsgroup msg is at the end of this message.

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From:   A.....
Sent:   Monday, December 08, 1997 2:05 PM
To:     Bob Shaver
Subject:        Re: MIDI from PIC devices

Hi.  Thanks for your reply.  I'm developing a MIDI Brass controller that
has sensors on each of the valves to switch between harmonic series pitch
classes to be stored in an EEPROM and to do freqency counting on the
signal from the instrument using a pick-up mic.  Each valve combination
chooses a set of 16 pitches and the freq. data narrows the pitch down to
one and outputs it via the serial port.  I also will run the audio signal
through an A/D convertor for Velocity data.  Where I am novice is putting
it all together and outputting realtime midi data.  There aren't too many
sources for that, so I hope you can help.
For the prototype I hope to send pitch and volume/velocity data.  I'm
not worried too much with pitch bend at the moment, but want to implement
that in the future.  Also, I'd like the option to map an A/D of the
acoustic signal to the breath control feature.  One thing that I'm at
odds with conceptually is note on/off with breath control.  Maybe you
have some insight.
I realize that a lot of these are very general questions and require a
lot of explanation in their entirety.  I hope you can bear with me. I
really am in need of some basic starting ideas for the MIDI
implementation.  I'm very familiar with MIDI and the spec.  I just am not
so experienced with the PIC.  My mentor in this project is a PIC
programmer, but isn't too well versed in MIDI.
What is your implementation of the PIC for MIDI?  It sounds interesting.
Thanks for your interest and I hope you might be able to give me a
starting shove in the right direction.

Alex Ruthmann

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On Mon, 8 Dec 1997, Bob Shaver wrote:

> I have just finished a project that sent and received MIDI, using a 16C73.  Ask away...
>
> Bob.
>

1997\12\08@195400 by Andrew Mayo

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Since MIDI is essentially just RS232 async but at a non-standard baud
rate (and of course at TTL levels), implementing the transmit/receive
logic is pretty straightforward. However, the baud rate is quite high
and will require a significant percentage of the processor's bandwidth
just to acquire/transmit the data. Of course, you could use a UART
device or more than one PIC.....

{Quote hidden}

1997\12\08@213415 by Peter van Hoof

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Negative , midi doesnt use ttl level but rather current loop. this makes
longer cables and higher noise resistance possible


{Original Message removed}

1997\12\08@214755 by Andrew Mayo

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Well, to be strictly accurate the input and output from the MIDI device
before the optocoupler is TTL as opposed to +/- 12V. The output is fed
to the optocoupler's diode and the input comes from the sending device's
optocoupler output transistor, pulled up by a resistor to +5V. So in
essence the PIC or other device is seeing TTL. There didn't seem much
point in mentioning this, since I assumed (perhaps wrongly) that the
requirement for a high-speed optocoupler is well known (it is specified
in the MIDI spec, in fact). The reason for optocoupling is to avoid
ground loops, btw, not specifically for speed or noise immunity.
Musicians tend to dislike hum.

{Quote hidden}

> {Original Message removed}

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