exper wrote:So, what is involved in getting MIDI into the monotribe then? Simply wiring a MIDI jack to the serial port inside?
More or less, yes.
Standard schematic for reference:
For MIDI in, you should ideally add an optocoupler to adhere to the MIDI standard, and to avoid ground loops when possible. You *can* skip the optocoupler, this is what I did when testing. However, since the microcontroller is 3.3 V and MIDI is 5 V, you need to add a resistor in series with the serial line, since the chip could be damaged by directly connecting voltages above 3.3 V.
Even doing that, you're going slightly outside the specified limits of the chip, even though the chip should probably be able to handle the pressure with the added resistor. I used an 820 ohm resistor which seems to work fine. However, I wouldn't do this for a production version of this mod. I will look into suitable optocouplers to use.
Similarly, for MIDI out, you can get away with just connecting two resistors (One that goes between 3.3 V and the power pin of the MIDI jack, and one that goes between the serial output and the serial pin of the jack.) Once again, you can get away with a slight modification of the MIDI standard. In a standard MIDI circuit, the job of the transmitting side is to light up a LED at the receiving side. There are three resistors (two on the transmitting side and one the receiving side) in place to prevent various kinds of damage, like output to output connection other faults.
The transmitting side will work in a standard circuit so long as it manages to light up the LED in the optocoupler on the receiving side. I found that replacing the 220 ohm resistors labelled Ra and Rc in the schematic above to 150 ohms works ok. Again, your mileage may vary. Although it's unlikely, some MIDI circuits may use some other brand of optocoupler than mine and not light up with just 3.3 V. And something like a bus-powered MIDI hub probably wouldn't work reliably or at all at only 3.3 V. Again, if I were to install this mod, I would probably go for 5 V operation.
Note however that MIDI out is pretty much useless. You only have your 8 sequencer steps, of course. And also, the CC data from the knobs lags an awful lot. If you wiggle a muff really quickly for a couple of seconds, it will take several seconds before that has been fully transmitted. I'll have to verify that this is not a problem with my computer or anything, but it looks as if the monotribe really is that slow at transmitting MIDI.
And I managed to get a few weird glitches when sending MIDI from Reaktor, such as hearing a weird noise, possibly the machine's self-tuning process. Maybe there was a good reason they didn't officially include MIDI in the product specifiation...
More info will come in a while.