Propeller Midi Circuit plz

computer guy

Does anyone have a circuit diagram for midi in and out on a propeller?

Thank you

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Check out my robot using the propeller RECONAUTOR

Ken Peterson

I did MIDI with a VIC-20 about 15 or so years ago...gosh that was a long time. A Google search will most likely provide a starting point. I doubt I can find my notes from back then.

BTW: didn't someone just post a very similar question?

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The more I know, the more I know I don't know.· Is this what they call Wisdom?

Post Edited (Ken Peterson) : 10/12/2007 4:10:47 AM GMT

Bob Lawrence (VE1RLL)

You can use the URL below to view a schematic used for another Microcontroller and make a few adjustments such as the supply voltage.

http://www.tigoe.net/pcomp/midi.shtml

computer guy

Would changing the 270ohm resistor on the input to a 10k make the circuit prop compatible.
Same with the output, would changing the 10k to a 270ohm get that to work.

Am trying to make my prop board more like an atari by giving it midi in and out for synthesis.

Thank you

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Check out my robot using the propeller RECONAUTOR

Ken Peterson

I imagine you could use the 10K for either. The value isn't that critical in this application.

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The more I know, the more I know I don't know.· Is this what they call Wisdom?

Ariba

Here are two possible circuits for MIDI IN/OUT. They are not tested but I don't see why they should not work.
The first is based on the circuit of the link above, but adapted to the Propeller (3.3V). The second is a simpler version with an optocoupler that is very popular in Europe, I don't know if this is also the case in USA (you can use also the 6N138 instead).

The value of the PullUp Resistor (270R in first circuit) depends a lot of the optocoupler. If you have one with digital output you can also use 10kOhm but if it is only a phototransistor-output, then 10kOhm is to high for a fast low to high transition at 31.25kBaud.

Andy

Edit: for the first circuit the serial output must be inverted (idle = Low) for the second not.

computer guy

Thank you for the circuits.
I am not very good with resistors and stuff.
Guess I will have to learn that sometime.

Thank you

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Check out my robot using the propeller RECONAUTOR

Phil Pilgrim (PhiPi)

270 ohms seems like an awfully stiff pullup on the collector of the photo transistor. For it to work with the transmit circuit shown, the optocoupler would have to have a CTR of at least 300% — and that's neglecting cable losses. But I've seen this same circuit in a number of places now. I wonder if it's just one of those typos that got copied a bunch of times and has taken on a life of its own.

-Phil

edlikestoboogie

Has anyone gone about making a good MIDI out/in object with note velocity and maybe even aftertouch?

mpark

I wouldn't call it "good", but this might give you some ideas: http://forums.parallax.com/showthread.php?p=774500

SSteve

Phil Pilgrim (PhiPi) said...
270 ohms seems like an awfully stiff pullup on the collector of the photo transistor.

Forgive the dumb question from a software guy, but does that mean we should use a smaller- or larger-value resistor?

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mpark

From one software guy to another, I think Phil means a larger resistor, but in my experience the circuit as shown works fine with the Propeller.

hinv

Hi mpark,

Were you feeding the second prop a 5mhz signal and using the PLL on the second prop, or were you feeding it 80MHz or something in-between?

mpark

There was no second prop. I used MIDI to communicate between a (music) keyboard and a prop.