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sachsm  
#1 Posted : Monday, April 2, 2012 2:05:36 PM(UTC)
sachsm

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I am only seeing a .9V voltage swing on the toslink output. It is enough for the Opus receiver but
I would also like to try driving a standard TTL input. The spec on the TORX module indicates that I should
have at least a 2V output. I have order a new optical interconnect cable but wanted to first see what to expect.
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Brian Donegan  
#2 Posted : Monday, April 2, 2012 2:11:30 PM(UTC)
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The module should be outputting TTL-level (3.3V). What are you measuring with?
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sachsm  
#3 Posted : Monday, April 2, 2012 2:42:42 PM(UTC)
sachsm

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Agilent DSO, 200 MHz. x10 probe. The I2S signals on the Opus board are 3.3V but the TORX output is ~.9V
In all other respects, the TOSLINK signal looks good, clean waveform, just low amplitude. I have tried 2 different
TOSLINK modules and they are both the same. Could it be the fiber cable?
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sachsm  
#4 Posted : Monday, April 2, 2012 3:04:37 PM(UTC)
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It appears that the 75 ohm resistor to ground (R1) on the Opus module is attenuating the TOSLINK signal.
What is the recommended hookup between the OPUS and the TOSLINK module?
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sachsm  
#5 Posted : Tuesday, April 3, 2012 8:26:50 AM(UTC)
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Ok, looking at the Wolfson WM8804EV1 evaluation board schematic, it seems that the recommended connection to the Toslink output is direct wiring to the
RX input on the 8804. I plan on removing the 75 ohm to ground and shorting out the .1uf series cap to accomplish this.
(It seems like it would be a simple matter to add a jumper to allow selection of TOSLINK or Coax on the Opus module)

Edited by user Tuesday, April 3, 2012 8:29:27 AM(UTC)  | Reason: Not specified
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Brian Donegan  
#6 Posted : Tuesday, April 3, 2012 8:29:50 AM(UTC)
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That will work.
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