Electronics > Beginners

USB

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ataradov:
You need to describe what you expect to see on those LEDs. Adding a simple logic gate as a buffer would be fine in most cases. But all you will see is both LEDs be dimly lit when the devices are connected.

Doctorandus_P:
At what speed is that USB bus working?

Renate:
As we've determined, you really can't throw LEDs directly across a functional USB circuit.

But...
A device as the first step of enumeration throws a 1.5k pullup resistor between its internal 3.3V source to either D+ (for FS/HS) or D- (for LS).
We can make a handy little tester to test this.
Connect two LEDS directly between D+ or D- to ground.
Feed your device with 5V and ground, but don't connect the D+/D- from your hub or whatever.
Plug in a LS keyboard and the LS LED goes on.
Plug in a FS/HS device and the HS LED goes on.
Plug in your Omnicron666 µC that you're developing a custom USB lib for and see if a LED goes on.
Plug in your ATMega32u4 with silly code and watch the LEDs toggle.

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