[Dprglist] OK to jumper XTAL OSC together?

John Swindle swindle at compuserve.com
Tue Dec 17 16:20:13 PST 2019

Thank you for offering to help. I am sending the photos to you. I highlighted the crystal and its thru hole pins.
Later,John Swindle

-----Original Message-----
From: Doug Paradis <paradug at gmail.com>
To: John Swindle <swindle at compuserve.com>
Cc: DPRG <dprglist at lists.dprg.org>
Sent: Tue, Dec 17, 2019 05:21 PM
Subject: Re: [Dprglist] OK to jumper XTAL OSC together?

John,    Can you take a photo or give the product @ of the boards?
Regards,Doug P.
On Tue, Dec 17, 2019 at 2:57 PM John Swindle via DPRGlist <dprglist at lists.dprg.org> wrote:

I always enjoy the DPRG meetings and competitions, and last week was great!
I have a question regarding my sonar project:
I'm using two cheap USB audio adaptors to measure the sound. The samples have to be very tightly synchronized. Each adaptor has its own 12MHz crystal oscillator as an external component on the PCB. I wonder if I can jumper one crystal to the other without damaging the clock driver.
I don't have the schematic. SIIG and VANTEC make the adaptor which uses the C-Media CM6206 containing audio DACs and ADCs.
A better approach is to use a TI, Analog Devices, or Maxim multi-channel simultaneous sampling ADC, and I plan to buy a TI evaluation board.
Another better solution is to use a multi-channel pro audio mixer/adaptor. I have one of those, but TASCAM stopped supporting mine a few months after I bought it, and the driver crashes Windows 10. Also, even if I got a newer adaptor, it would be much larger, physically, than what I want on a robot. OK for prototyping, but not good for demonstrations.
I've closely synchronized the adaptors by having one of them give a click track to the other one. The software resamples the second adaptor's samples based on errors in the recorded click track. The click track software does a good job of handling the persistent difference in the two oscillator frequencies, but I have not added code to handle jitter. A hardware solution would be more like what the final solution looks like.
(While writing that software, I realized that the click track just forces the second adaptor to suffer the first adaptor's jitter, meaning I have not eliminated jitter. Nevertheless, the results are nearly pristine for all of the ADCs within an adaptor which are jittering together, so if I get the ADC in the other adaptor to jitter with the first one, the results would probably be very good.)
Best to y'all! See you next year.
John Swindle
DPRGlist mailing list
DPRGlist at lists.dprg.org

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