USB Host on Teensy 4.1, no power, no data, two brand new boards

honey_the_codewitch

Active member
I ordered a teensy specifically for the USB host capabilities.
It didn't work.
I ordered a second teensy, again specifically for the USB host capabilities.
Unfortunately repeating the same thing over and over again is not yielding different results and I'm tired of throwing money at something that should have worked out of the box.

There is no source code because it didn't get that far.

The only connections that I have made are

1. MicroUSB to power the Teensy through it's built in USB device port.
2. GND/VBUS/D+/D- on the inner USB Host pins to a USB-A port breakout.
I've verified that wiring 12 times in 3 days, at least, and on two different boards.

No power to the device plugged into the host.

Multimeter laughs at me when I put it right on the board. No results.

Why in the world would a Teensy be marketed as having USB hosting capabilities that appear to be no connect?
 
Why in the world would a Teensy be marketed as having USB hosting capabilities that appear to be no connect?

Because the USB host power is controlled by a TPD3S014 current limited switch.

vhost.png

You won't get any power delivered to the +5V USB host pin unless you call the USBHost_t36 library begin() function or otherwise write code which drives the EMC_04 pin to logic high. A 100K resistor is present to assure the default condition is USB host power does not turn on until software enables the current limited switch.

This is by design. USB is about more than just data signals. Proper power delivery is a critically important part of USB. Without a current limit chip and large enough capacitor, hot plugging USB devices or just charging up that capacitor when Teensy 4.1 itself is powered by a USB cable can cause a power brown-out condition that reboots Teensy's processor.

Most of the Arduino USB host shields on the market have this problem where hot plugging USB devices crashes the microcontroller. Avoiding a brown-out condition when the upstream power is another USB cable is not easy. Teensy 4.1 was designed with this circuitry to give the best chances of hot plugging working even when running from another USB cable.
 
Thank you so much!

I've been tearing my hair out on google, on reddit, everywhere I could find to try to run this problem down. It had occurred to me that it might be software controlled, but I dismissed it, because I hadn't seen that before (even my PC doesn't work that way) and because who does that and why?

Well, now I at least can understand somewhat, if not fully, the why.

I do wish this was in a Teensy FAQ somewhere, or maybe it was and I missed it?

THANK YOU THANK YOU THANK YOU.

I knew after the second board that it had to be a problem on my end, but I was at a loss.

This has been vexing me for too long and I was at my wits end. You don't know how grateful I am right now. :)

Edit: I just realized you are the author of the library, and the library does not have associated license information in it. I cannot use Arduino's repo because I'm on PIO, so I must ship your source with my project under /lib for it to build. What is your licensing for this library? I want to dot my i's and cross my t's here. Also I don't think I'll have to modify it, but on the off chance I do (like I had to with the MAX32whateverE chip library) it would be nice to know the terms. Thanks in advance!

Edit 2: I found it. Never mind. Thanks!
 
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