About USB signal

[SimonQian]

A user of AVRminiProg give me a picture about the USB signal.
He test the AVRUSB unstable on his PC.



By my side:

And it's muuuuuch better.

Will it solved by increasing the resistor between USB and AVR?

[apollononnno]

Hi Simon
I watch an image and think whether it is the impedance matching of slightly loud sight.
Is the examination possible to become 50 Ω for trial?

The part of the underline is a mistake.
It is assumed that I use MPU of 5V and connects 75 Ω and 150 Ω to GND on an MPU terminal.
The signal from USB inputs it into MPU when I join to a USB connector from a linkup of the resistance without damping.
I damp, and the signal from MPU is output from 5 by 3.3v.

I noticed that I examined Schematic well for a great mistake.
It cannot generate 3V that are necessary for 15kΩ to let you recognize it first.
When I do 220 Ω and 100nF in series between a signal line of D+ and D- when I consider 68 Ω which can possess avr side of fullspeed and had better use it for adjustment revision, I judge it.

I predict that 3.3v, substitution of 1.5kΩ can do it in PULLUP of 2.2kΩ and 4.7kΩ.

[christian]

The ringing suggests that the user either has a very inductive cable or that he omitted the resistors. The edges on the screen photo are pretty sharp, so it should be possible to increase the series resistors to suppress ringing. The user can also try to add capacitors to D+ and D- (several 10 pF range).

But my first recommendation would be to swap the cable (if the effect is real and not caused by the cope...).