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Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
I was looking around TI the other day and saw there PCM2704 chip. Its a usb DAC that should be plug and play with just a few external parts. It seems like a lot of people have made what I'm trying to do and it worked pretty well.
I checked the wiring and the supply voltages. I think my problem is the crystal oscillator. When I scope it, it is not oscillating at all. The XTO pin just has 3.3V on it and the XTI pins has about a volt. Here's the link to my crystal . I have cleaned all the flux off many times with botch acetone and rubbing alcohol. Any ideas? Thanks!
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
Crystal oscillators like for microcontrollers usually have something like a 5pF capacitor to ground on each side of the crystal where it connects to the chip. Usually the chip provider will provide some guidance on this, do you have any such capacitors in your circuit?
Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
Yeah the crystal lists 20pF load capacitors which I am using. There is also a 1M resistor in parallel with the crystal leads which I have not seen used on uC but is shown in an application schematic in the data sheet. What is this for?
Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
I think my problem might be with placement. I got the oscillator to work once and the entire circuit functioned perfectly. I have the crystal about a half inch from the chip with the load capacitors right next to the crystal. There is also a ground plane under the crystal up to the chip.
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Problem with homemade usb soundcard
