External power MIDI teensy 3.6

J

Jojomonk

Member
Hello,

I'm building a small 2 in 2 out midi interface with a teensy 3.6.
2 questions: is it possible to power the teensy by the midi in cable?
Is it possible to automatically switch between USB power supply and midi power supply?
I would like to be able to power the interface by midi when it is not connected to usb, and power it to usb when it is connected to a pc.
I saw a tutorial on the site, but it's with another teensy card, is there a tutorial for the teensy 3.6?
 
A Teensy draws about 50mA of current. As far as I know it is not meant and not specified to power something beside the optocouplers from the MIDI port - but as several devices do this it seems to be working and I would expect that this is the case for a Teensy 3.6, too. Possibly it depends on the MIDI device if this is working. You can feed the 5V from the MIDI line to the Vin of the Teensy. If there should be 3.3V that would be not enough voltage.

It has to be prevented that USB and Vin (from your MIDI line) are both connected to voltage at the same time. So there has to be some sort of switch to disconnect Vin when power comes from USB. Or maybe a simple diode for protection is enough to prevent any current flow? If the voltage drop from 5V stay over 3.6V it should work?

If you give us a link to the tutorial other could check it. The connection or separation of Vin and USB power is in general the same on different Teensy versions.
 
Option #3 from that page is an option also for a Teensy 3.6 (and also others):
Put one diode between 5V from MIDI and Vin.
Cut the trace between the pads to disconnect USB 5V and Vin (as described on the pinout card).
Put one diode between those pads (or from the USB 5V pad or VUSB pin to the Vin pin).

Using the proposed 1N5817 diode with 0.3V drop leaves enough voltage for the Teensy.

This is more a protection against current flow between Vin and VUSB. There is no complete disconnection of the MIDI Vin when VUSB is used. If that is important, a more complex circuit would be necessary.
 
Ok, thank you, so no danger if the teensy receives noon current and usb at the same time?
In what direction should the diode be put on the teensy?
 
Jojomonk said:
I'm building a small 2 in 2 out midi interface with a teensy 3.6.
2 questions: is it possible to power the teensy by the midi in cable?
Click to expand...
It is possible, and there are indeed a few commercial products that do this.
It is not advisable:

  1. DIN MIDI is a current-loop digital signalling system and the current is only intended to be enough to power the LED in the opto-isolator.
  2. Using MIDI for power couples the signal ground to the MPU ground thus defeating the point of the opto-isolator
  3. The voltage could be 5V but could also be 3V3
  4. There are combined MIDI+power solutions which use the spare 2 pins on the 5-pin DIN to provide 5V power. They are not common, and tend to be aimed at specific products, like breath controllers
 
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