Powering USB hub and Teensy 4.1 from same power supply

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dk8moore

New member
Hello there! 🌚

I'm building a MIDI instrument with USB ports to control (or be controlled by) other MIDI devices.

From my (in)experience, initially I thought connecting a passive USB hub to the Teensy could do the trick, but then I realized I didn't consider the limited power that the Teensy - very reasonably - can output to power external USB devices through its USB host module.

So now I'm wondering about what could be the most reasonable approach to transform my passive USB hub into an active one, using the same external power supply that is currently powering the Teensy - which is a regulated 5V 3A power supply I found on a DIY website. The power supply has a trimmer to change the output voltage by ±2V.

Let's say that while a 2A fuse could probably solve all my problems, I'd like to understand if there are better options maybe involving some specific circuits to limit the current drawn by a part of the system: ideally I'd like to be sure that the USB hub can potentially draw 2A from the power supply but not more than that, leaving enough room (1A) to power the Teensy and all the other modules in the rest of the system.

What would you guys suggest for my case scenario?

Thanks in advance :)
 
About what and how many USB devices are we talking exactly? Have you measured the current? I was surprised that for many devices it stays way below 500mA both for controllers with some leds or even instruments. I don't know instruments which need more power which are powered over USB. Only scenario I can think of is if you should connect a lot of devices at the same time.

For the limits, see, e.g. this thread:

Regarding your question about the fuse: What is the idea behind it? Having some kind of protection? I don't see a real problem to use a 3A power supply for both the Teensy and the USB hub. Here again is the question if you really need that current. A quality power supply should have several protection circuits including a temporarily shut down if too much current is drawn. Even the cheap ones have this often.

Depending on the type of the devices and audio connections you could run into problems on the audio lines but this is hard to predict.
 
All the instruments I need to (potentially) power draw at most 500mA each (from the manufacturers' sites), and there are at most three of them... BUT having a 4 ports hub at my disposal, I'd also like to connect an iPad for at least maintain its charge status and that's where I'm concerned about exceeding total current capabilities, as I reckon that USB 3.0 ports output up to 900mA.

I get your point though, probably I'm just overthinking it and maybe it's not that necessary?

Regarding the fuse (or even better a Polyfuse maybe?), the idea behind it is to "isolate" the USB hub from the Teensy part of the circuit, so that if the devices connected to the USB hub draw a lot of current, the Teensy part of the circuit will not be affected, as that part (USB hub) will be promptly cut out from the power supply.
Does it make sense? I've seen this suggested in this other thread.
 
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