Xmega32a4u USB Shielding and LCD Hang problem

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Hi,

I am using XMEGA 32A4u.

The PCB is fixed in a plastic cabinet and the USB connector is mounted on an Aluminium plate.

In my project Xmega device is self powered and VCC from USB is left unconnected.

 

I am using pfleury_lcd LCD library and sysclk_init() function to initialize clock with following settings.

 

#define CONFIG_USBCLK_SOURCE     USBCLK_SRC_RCOSC
#define CONFIG_OSC_RC32_CAL      48000000UL
#define CONFIG_OSC_AUTOCAL          OSC_ID_XOSC//OSC_ID_RC32MHZ
#define CONFIG_OSC_AUTOCAL_REF_OSC  OSC_ID_XOSC//OSC_ID_USBSOF
#define CONFIG_SYSCLK_SOURCE     SYSCLK_SRC_RC32MHZ
#define CONFIG_SYSCLK_PSADIV     SYSCLK_PSADIV_2
#define CONFIG_SYSCLK_PSBCDIV    SYSCLK_PSBCDIV_1_2

 

Problem:

LCD hangs on power on and works only when we approach our hand near ground points.

 

I am not sure where to look for this problem.

I have referred to AVR1017: XMEGA - USB Hardware Design Recommendations and I am using following schematic for USB connections.

 

Can there be a problem due to LCD library in reading busy pin due to which the LCD hangs ?

 

 

 

 

Last Edited: Sat. Dec 6, 2014 - 05:17 AM
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Problem:

LCD hangs on power on and works only when we approach our hand near ground points.

 

Hmm. This sounds like something not connected or really high impedance. Try checking your ground points with an ohm meter. Perhaps you have an input floating or pullup not enabled when you think it is? These are when I first look for when I have something that mysteriously starts or stops working when I reach for it. "Oh, that pin isn't soldered down."

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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Problem:

LCD hangs on power on and works only when we approach our hand near ground points.

 

Hmm. This sounds like something not connected or really high impedance. Try checking your ground points with an ohm meter. Perhaps you have an input floating or pullup not enabled when you think it is? These are when I first look for when I have something that mysteriously starts or stops working when I reach for it. "Oh, that pin isn't soldered down."

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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Hi,

The funny part is we wired over 75 PCB's and only 15 of them are diagnosed with this problem.All the boards are exactly alike.

This kind of problem was not there with ATmega part numbers.

 

Are there any specific pins on the IC which needs to be pulled up or grounded ?

 

 

 

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75 PCB's and only 15 of them are diagnosed with this problem.

Have you ever heard of dry joints, broken tracks aor other production faults?

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Odd how some of us stutter when we post.

 

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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I think most "experts" say never connect the USB cable shield to your board, or possibly connect it through a resistor/capacitor.  They say a direct connection causes your board to radiate like an antenna.

 

I'm not a ground expert and I don't know if your connection is a problem.  I leave my shields unconnected.

 

 

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If your board is not connected to any other grounds, I would connect the USB gnd wire directly to the board ground.