I am developing a hardware where I would like to use an SDR circuit (RTL2832). However on the first prototype the circuit does not work. It has a USB interface however when I connect it to PC the device is not recognized.

On Windows machine I got the following error:

Unknown USB Device (Device Descriptor Request Failed)

On Linux:

usb 1-1: device descriptor read/64, error -71

The RTL2832 circuit is pretty simple. It has some capacitors, eeprom, its own DCDC converter for 1.2V and a USB interface. The DP and DM lines are connected with 27R to the USB interface.

The circuit got the 5V from USB, 3.3V is made by an LDO from USB 5V. The 3.3V is present, 1.2V is produced by the chip, there are no shorts on the board, no high current consumption, no heating, electrically it should work.

RTL2832 schenatic

The USB lines looks like this:

enter image description here


Seems like the DM line is on 2.5V and there is a small ~100mVp-p signal on it.

Any idea what to debug? What can be the issue?

  • 3
    \$\begingroup\$ I haven't read the datasheet for your RTL2832, but maybe you need to load USB descriptors (and possibly sums other configuration settings) into that external EEPROM. \$\endgroup\$
    – brhans
    Nov 20, 2021 at 20:04
  • \$\begingroup\$ Whose MFG/device descriptor did you program into it? (presumably that's what the 2402 does). Have you installed drivers for that device ID? \$\endgroup\$
    – user16324
    Nov 20, 2021 at 20:07
  • 2
    \$\begingroup\$ @brhans The errors suggest the descriptor read failed, not that an unrecognized descriptor was read. Of course you may still be right about needing to load the EEPROM. \$\endgroup\$
    – TypeIA
    Nov 20, 2021 at 20:11
  • \$\begingroup\$ Good catch, I have not upload anything to eeprom. I will read after this. Thanks! \$\endgroup\$
    – D_Dog
    Nov 20, 2021 at 20:19
  • 1
    \$\begingroup\$ @D_Dog - Hi, If you are willing & able to help Hamidreza, please contribute on their question here. They are unable to reply to comments here (not enough points). They have been breaking the site rules by writing non-answers and I have been trying to help by moving them to become comments. I have now stopped doing this (it's not sustainable for ongoing discussion) so the only method to help Hamidreza is on their question, which I linked above. Thanks. \$\endgroup\$
    – SamGibson
    Jul 18, 2022 at 13:30