LUFA and USB Modem frequent detach

Go To Last Post
7 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi!

I've got a problem with LUFA that detaches USB modems frequently and fast.
Namely if my code initializes a USB modem, sends an initialization string, sends the ATDT* command and the mobile network says NO CARRIER, the modem would detach right away in 80% of cases.

Any ideas why this may be happening?

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

An idea crossed my mind. Did anyone out here try to work with USB modems? I've got a transistor that open's up the power channel to the USB bus when the AVR raises level on the corresponding pin. The transistor is 0.6A. The USB Spec for 1.0 and 2.0 is 0.5A, but it may be, as I think, that the modem suddenly wants more and the transistor won't let that power pass, so that it comes ot that I underfeed it. Any thoughts?

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Can you show us your circuit?

Just a thought ... a 2 ton truck is not carrying 2 tons all the time. Just because your transistor is rated to carry 600 mA doesn't mean that it is ... get my drift?

Cheers,

Ross

Ross McKenzie ValuSoft Melbourne Australia

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I strongly suspect this is a problem with the VBUS level dropping due to current spikes from the Modem. I remember Mike having issues with his 3G modems - despite the USBKEY supposedly being good for 1A he still needed an external power supply to keep up with the large current spikes demanded by the modem to prevent it from causing re-enumerations randomly.

- Dean :twisted:

Make Atmel Studio better with my free extensions. Open source and feedback welcome!

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

We've changed the transistor to IRLML5203 (2.6A) from IRLML5103 (0.6A) and now it is fine.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

My worries are now with the stabilizer of the entire board which is 1.5 Amps. The chinese Huawei modem isn't documented that well to understand how high the spikes may go and if they are too consuming that may switch off the whole thing altogether.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Put a honking great big cap on there and you should be fine. I remember the problem being mostly spikes when the modem started up, rather than continuously very high current draw.

- Dean :twisted:

Make Atmel Studio better with my free extensions. Open source and feedback welcome!