I know that I can build a custom MIDI-Controller with some external electronics. But isn't that possible to skip that part and connect the resistors directly to Pi?
After I want to read the measurements in Pure Data.
I know that I can build a custom MIDI-Controller with some external electronocs. But isn't that possible to skip that part and connect the resistors directly to PI?
After I want to treat the measurements in Pure Data.
Yes, you can directly extract the midi signals from the 5 pin socket and use a scope to measure the signals' frequency magnitude etc. The midi signals are not too different from RS232, so even using hardware to do some adaptation, with the help of opto couplers to do simple level shifting/isolation to Rpi 3V/5V compatible, it won't be that hard. One difficulty I encountered is that it is rather difficult to find the very old 5 pin plug, you might need to search those Hifi shops selling old accessories.
The following picture show roughly the midi socket pinouts. The references below give more details.