[Gmecm] Any USB developers out there?

Thu Nov 9 21:39:26 UTC 2006

Hi Craig, this app (USB to VPW converter) will always be connected to
vehicle power so I'm not using the USB power option.  VBUS (power from
the USB cable) has a bypass capacitor to ground but that's it, and the
circuit is always powered via VCC from the 5V regulator.  That's not
what the schematic shows but that's been changed on my PCB. 

--steve

> -----Original Message-----
> From: gmecm-bounces at diy-efi.org 
> [mailto:gmecm-bounces at diy-efi.org] On Behalf Of Craig Moates
> Sent: Thursday, November 09, 2006 3:31 PM
> To: gmecm at diy-efi.org
> Subject: Re: [Gmecm] Any USB developers out there?
> 
> Not sure about the 2455, but could you be having Vcc and Vusb 
> contention? Two separate power supplies? With these low-power 
> circuits, I've typically allowed them to be USB bus-powered 
> in parallel with whatever target device power (OBD2 regulated 
> etc) through a pair of schottky diodes. That has always 
> worked well, you end up with 4.9v or thereabouts which is adequate.
> 
> What you describe below could be consistent with this sort of 
> thing. Maybe just lift the Vusb and jumper it over from Vcc 
> to see what happens.
> 
> Best regards,
> Craig Moates
> 
> 
> 
> ----- Original Message -----
> From: "Steve Ravet" <Steve.Ravet at arm.com>
> To: <gmecm at diy-efi.org>
> Sent: Thursday, November 09, 2006 2:52 PM
> Subject: RE: [Gmecm] Any USB developers out there?
> 
> 
> Craig, thanks for the suggestions.  I brought it in to work today and
> found something interesting.  When the board is powered up, 
> no USB cable
> connected, the 20 MHz crystal oscillates fine.  When I plug in the USB
> cable the OSC gets distorted, then goes flat after about 1 
> sec.  As soon
> as I pull out the USB cable the OSC comes back.  This is some kind of
> loading issue?  The PIC has some internal settings related to the OSC,
> I'll have to double check them.
> 
> thanks,
> --steve
> 
> > -----Original Message-----
> > From: gmecm-bounces at diy-efi.org
> > [mailto:gmecm-bounces at diy-efi.org] On Behalf Of Craig Moates
> > Sent: Thursday, November 09, 2006 11:51 AM
> > To: gmecm at diy-efi.org
> > Subject: Re: [Gmecm] Any USB developers out there?
> >
> > Steve,
> >
> > Definitely check the crystal and capacitor areas. Those are
> > ceramics you are using for the 18pF set? Check that it's set
> > up for 18pf on the xtal desired capacitance?
> >
> > I'd be possibly concerned with how the trace is run on that
> > 1M there by the xtal. Could be some induced stuff going on?
> > Also, doesn't the pic have the load built in?
> >
> > Considered adding caps to gnd on the USB lines coming in?
> > Could be picking up some noise, I like to put like some 
> 47pF on there.
> >
> > I assume you've tried even after a hard reset via your switch
> > in there, right? Just wondering about brownout issues and
> > that sort of thing.
> >
> > Have you tried it with just the USB, PIC, xtal, and
> > resonator/decoupling caps connected? Could help to step in
> > slowly to see what's 'not' causing the problem. I know I
> > always get excited, assemble the whole thing, and then step
> > back to find one trace or leg that isn't going where it should.
> >
> > Best regards,
> > Craig Moates
> >
> >
> >
> > ----- Original Message -----
> > From: "Steve Ravet" <Steve.Ravet at arm.com>
> > To: <gmecm at diy-efi.org>
> > Sent: Monday, November 06, 2006 10:02 PM
> > Subject: RE: [Gmecm] Any USB developers out there?
> >
> >
> >
> > > -----Original Message-----
> > > From: gmecm-bounces at diy-efi.org
> > > [mailto:gmecm-bounces at diy-efi.org] On Behalf Of Paul Smith
> > > Sent: Monday, November 06, 2006 8:10 PM
> > > To: gmecm at diy-efi.org
> > > Subject: Re: [Gmecm] Any USB developers out there?
> > >
> > > I would'nt call myself a USB expert but would be willing to
> > > help if you do not get any other volunteers.
> > >
> > > I have worked a bit with the 18f2550 series that supports USB.
> > >
> > > Paul
> > >
> >
> >
> > Hi Paul.  I have uploaded the project to the TWiki page:
> >
> > http://www.diy-efi.org/twiki/bin/view.pl/Gmecm/UsbVpw
> >
> > I think the problem is in hardware instead of software.  I 
> am testing
> > the board with a keyboard/mouse demo that is supposed to move
> > the mouse
> > in a circle and send keystrokes.  This firmware works on 
> the PIC demo
> > board that I bought, but it doesn't work on my PCB.  I ran 
> usbview.exe
> > to see that most of the enumeration is correct except the
> > last 4 items:
> >
> > my board                              demo board
> > ----------------------------------------------------------------
> > Current Config Value: 0x00            Current Config Value: 0x01
> > Device Bus Speed: Low                 Device Bus Speed: Full
> > Device Address: 0x00                  Device Address: 0x01
> > Open Pipes: 0                         Open Pipes: 1
> >
> > That stuff is clear as mud to me.  The thing that stands out
> > is the Bus
> > Speed.  I don't know why my PCB shows up as Low while the
> > demo board is
> > Full.  I have checked the D- and D+ lines and the pullup is
> > in the right
> > place.
> >
> > I am using the PIC18F2455.  I posted to the microchip 
> forums also and
> > got some suggestions but haven't found the answer yet.  
> That thread is
> > here:
> >
> > http://forum.microchip.com/tm.aspx?m=185797
> >
> > thanks for any help,
> >
> > --steve
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