External Power AND sending MIDI data via USB port ?

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napkey

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Hi everyone,

I'm currently working on a musical instrument, which I'll bring with me on tour, so it has to be perfectly safe :)
I need my teensy 3.2 to send midi data to a synthesizer. The problem is the synthesizer should be powered via the USB connection, but the teensy ALSO has to be powered via USB :'(
So my first suggestion is :
- Get a USB to MIDI 5 Pin Cable
- Have external power for the synthesizer to its USB port and use the 5PIN MIDI Input PORT
- Have external power for the Teensy 3.2 and send DATA to the USB to MIDI 5PIN cable through the Teensy USB PORT

Do you think it would work ? Can the USB port of the Teensy be used only to send data, and not to receive power supply ?
If you have any other ideas on how I could get all this done in a better way, I'd really appreciate :)

Thanks a lot for your time and patience,

Cheers
 
First, to answer your question, yes the USB port on Teensy can do data but not power. On the bottom of Teensy 3.2 you'll find a pair of pads to cut apart, which separates VUSB from VIN. Once cut, Teensy is disconnected from the USB power.

Something I didn't see in your question is whether this synth has a USB host or device port. This matters. USB only works if you have devices plugged into a host. The USB port on Teensy 3.2 is USB device only.

If your synth is a USB device, then you'd need Teensy to communicate as a USB host. Only Teensy 3.6 has that capability, on it's 2nd USB port. If you were to use that port, you could simply not connect the red wire if you want data only.
 
Hi Paul, thanks for your answer.

This synth has a USB device port, it's actually a module synth, here's an image of it :
waldorf-streichfett-796142.jpg
But the thing is, it draws power from the USB port, so I can't really use it, I'd like to use its MIDI 5PIN input for that.

Also, the Teensy 3.2 I'm using is part of the "Chord Strummer" Project :
https://www.tindie.com/products/yoe/t-chordstrum/

Which basically sends MIDI signal to the USB port when strumming the capacitance nodes on the upper right of the board.
What I thought would work best is :

Teensy ---> USB cable ---> USB TO MIDI Hub (which is capable of powering the Teensy via its USB port) ---> MIDI out to MIDI IN of the synth

I don't understand, hen you say the USB Port is USB Device only, do you mean it can't send MIDI Data ? Only receive it ?
 
Teensy 3.2 can not talk to that synth, at least not using USB.

To make this work, you need Teensy 3.6 and this cable.

https://www.pjrc.com/store/cable_usb_host_t36.html

Also needed are 5 pins soldered to Teensy 3.6 (for the cable to plug in), and a regular USB cable to connect between that short host cable and the synth. For software, you'd use the USBHost_t36 library to communicate with the synth.
 
If you want to understand these finer details about USB, here's a link to the USB 2.0 spec.

https://www.pjrc.com/teensy/beta/usb20.pdf

This is a huge PDF, but the info you need is in chapter 4 which is a short and easy read. USB is a very complex communication protocol with lots of very specific terminology. If you want to chat about USB design stuff, you really need to at least read chapter 4 to come up to speed on the key concepts and lingo.
 
Hi Paul, thanks a lot for all these precious information. I'll get right into it and learn how to communicate with the synth via USB.
I'm still curious though as how the teensy 3.2 can send MIDI data to a computer DAW, but not to a synth ?
Thanks again for your help :)
 
You can power the synth with a usb charger and control it with DIN MIDI from Teensy powered separately.

You only need to cut the trace if you're communicating as a usb device while being powered by another source but that's not an issue here as the power has to come from the host and that would be the Teensy (if you do usb midi).

For DIN MIDI you need a bit a hardware but if you are limiting to outbound only it's very minimal - the plug and two resistors.

Or you could try to host USB MIDI on a Teensy 3.6 with the added cable as Paul indicated.
 
oddson said:
You can power the synth with a usb charger and control it with DIN MIDI from Teensy powered separately.

You only need to cut the trace if you're communicating as a usb device while being powered by another source but that's not an issue here as the power has to come from the host and that would be the Teensy (if you do usb midi).

For DIN MIDI you need a bit a hardware but if you are limiting to outbound only it's very minimal - the plug and two resistors.

Or you could try to host USB MIDI on a Teensy 3.6 with the added cable as Paul indicated.
Click to expand...

Thanks a lot Oddson, I've seen the DIN MIDI hardware solution you mentioned, it seems quite simple and effective :)
I talked today to the creator of the "Chordstrum" (the guy who made the original teensy controller Omnichord-like) and he told me I could just use this USB to DIN MIDI Converter, that would act as a host and pipe the MIDI DATA from the Teensy to the Synth : http://www.hobbytronics.co.uk/usb-midi-converter
That way there would be no additionnal coding to do as the Teeny wouldn't be modified. In my opinon that would be the best and simplest solution. What do you think ? Thanks a lot
 
napkey said:
I'm still curious though as how the teensy 3.2 can send MIDI data to a computer DAW, but not to a synth ?
Click to expand...

Your computer running DAW software is a USB host. The synth is a USB device. They're very different.

In USB, devices can never communicate with each other. They only communicate with the USB host.
 
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