View Full Version : Solved MIDI-to-USB doesn't play well with Prop Plug

02-20-2012, 01:42 AM
I have a cheapo generic MIDI-to-USB interface connected between a MIDI keyboard and my laptop. When I press a key on the keyboard, a green LED on the MIDI-USB device flashes and the software on the laptop makes a sound. So far so good. Unfortunately, when I plug in a Prop Plug (with a live Propeller on the other end), the MIDI-USB device stops working (no more green flash, no sound).

Any ideas to get both the MIDI-USB and Prop Plug working concurrently?

EDIT: It's working now. Apparently I had a bad solder joint.

EDIT2: Actually, it appears that the problem is in the MIDI-USB box. I have two of them and only one has the problem.

02-20-2012, 02:21 AM
Make sure you have the latest drivers for both devices and that they are installed before you connect either device. You may have to go to the device manager and remove all the existing USB drivers for these devices first. You can also check to make sure the USB to MIDI ddevice is using a legitimate device signature.

average joe
02-20-2012, 02:11 PM
What is the hardware connection you are using with the prop? I have not implemented MIDI on the prop yet but will be doing so soon. Have you tried plugging the keyboard into the prop?

Phil Pilgrim (PhiPi)
02-20-2012, 04:21 PM

Does the MIDI-USB adapter emulate a serial port? If so, it could be that both it and your PropPlug are using the same COM port number. In that case, just reassign one of them.


02-20-2012, 08:51 PM
Does the MIDI-USB adapter emulate a serial port?

This was my thought as well. I think it would pretty much have to, as MIDI data is a set 31250 baud. At least that's the way it works on a Roland I have, where the driver is assigned to a COM port.

-- Gordon

02-21-2012, 07:28 PM
Thanks all. Further investigation reveals that the problem only manifests itself when the MIDI input to the MIDI-USB device comes from a Prop-based MIDI OUT circuit (as discussed here: http://forums.parallax.com/showthread.php?137345-MIDI-troubleshooting-help-pliz); the MIDI-USB works OK without a Prop Plug but stops working once the Prop Plug is connected (to a different Propeller, not the one sending MIDI data). With MIDI from a commercial keyboard (e.g. Casio) the MIDI-USB works fine with or without a Prop Plug.

Apparently there's still some subtle difference between my Propeller's MIDI OUT and "regular" MIDI OUT.

Phil Pilgrim (PhiPi)
02-21-2012, 07:45 PM

If you suspect a hardware incompatibility, you could try going back to the 5V circuit, with two 220R resistors, and use a 74HCT buffer or transistor inverter driven by the Prop.